Chapter Summaries Flashcards
(18 cards)
11.0
- 1 The benefits of regular physical activity include enhanced heart function, improved balance, reduced risk of falling, better sleep habits, healthier body composition, and reduced injury to muscles, tendons, and joints. A gradual increase in regular physical activity is recommended for all healthy persons. A minimum plan includes 30 minutes of physical activity on most (or all) days; 60 to 90 minutes per day provides even more benefit, especially if weight control is an issue.
- 2 A good fitness program is one that meets a person’s needs. To reach goals, fitness program planning should consider the mode, duration, frequency, intensity, and progression of exercise, as well as consistency and variety. Before starting a new fitness program, discuss program goals with a health-care provider. Also, assess and record baseline fitness scores. Most new exercise programs should start with short intervals of exercise at the lower end of the maximum heart rate target zone and work up to a total of 30 minutes of activity incorporated into each day. To prepare and recover safely from an exercise session, a warm-up and cooldown period should be included.
11.3 At rest, muscle cells mainly use fat for fuel. For
intense exercise of short duration, muscles mostly use phosphocreatine (PCr) for energy. During more sustained intense activity, muscle glycogen breaks down to lactic acid, providing a small amount of ATP. For endurance exercise, both fat and carbohydrate are used as fuels; carbohydrate
is used increasingly as activity intensifies. Little protein is used to fuel muscles. Fuel sources for muscle cells can be estimated based on percent of VO2max.
11.4 Physical activity has many effects on the body. The most pronounced effects are typically seen in the muscular, circulatory, and skeletal systems. The body contains 3 major types of muscle tissue: skeletal muscle, smooth muscle, and cardiac muscle. Skeletal muscle is composed of 3 main types of muscle fibers, which have distinct characteristics. Prolonged, low-intensity exercise, such
as a slow jog, mainly uses type I muscle fibers, so the predominant fuel is fat. As exercise intensity increases, type IIA and type IIX fibers are gradually recruited; in turn, the contribution of glucose as a fuel increases. Type IIA and type IIX fibers also are important for rapid movements, such as a jump shot in basketball. The relative proportions of the 3 fiber types throughout the muscles of the body vary from person to person and are constant throughout each person’s life. With training, muscle strength becomes matched to the muscles’ work demands. Muscles enlarge after being made to work repeatedly. Repeated aerobic exercise strengthens the heart and increases in the number of capillaries in muscle tissue; as a result, oxygen can be delivered more easily to muscle cells. Another adaptation that occurs with exercise is increased bone density.
11.5 Athletic training and genetic makeup are very important determinants of athletic performance. Monitoring body weight is an easy way to
assess the adequacy of calorie
intake. Athletes should strive to
maintain weight during competition
and training. Athletes should obtain
at least 60% of total energy needs from
carbohydrates. Carbohydrate-loading
regimens usually increase muscle glycogen
stores 50 to 85% over typical conditions.
Carbohydrate loading is for athletes who
compete in continuous, intense aerobic events
lasting more than 60 to 90 minutes. A fat intake of
15 to 25% of energy is generally recommended for athletes. Typical recommendations for protein intake for most athletes range from 1.0 to 1.7 g of protein/kg of body weight. The extra protein is needed for the repair of tissue and the synthesis of new muscle that results from training. Vitamin and mineral needs are the same or slightly higher for athletes, compared with those of sedentary adults. The female athlete triad consists of 3 conditions: menstrual disorders, low energy availability, and low bone mineral density.
11.6 To maintain the body’s ability to regulate internal temperature, athletes must consume sufficient fluids because dehydration leads to a decline in endurance, strength, and overall performance and sets the stage
for heat exhaustion, heat cramps, and potentially fatal heatstroke. During exercise, the recommended fluid
status goal is a loss of no more than 2% of body weight.
To prevent hyponatremia, athletes should drink beverages containing sodium and should consume enough fluid during exercise to minimize the loss of body weight. Most experts recommend drinking sports drinks instead of water.
11.7 The composition of food eaten before, during, and after athletic events or exercise training sessions can affect performance and the speed with which the athlete recovers from the exercise bout. Pre-exercise training meals keep the athlete from feeling hungry before and during the exercise bout and maintain optimal levels of blood glucose for the exercising muscles. The pre-exercise meal should be high
in carbohydrate, non-greasy, and readily digested. For sporting events lasting more than 60 minutes, consuming carbohydrate during activity can improve athletic performance. Carbohydrate-rich foods should be consumed 30 minutes after exercise and again 2 hours after exercise.
11.8 An ergogenic aid is a nutritional, psychological, pharmacological, mechanical, or physiological substance or treatment intended to improve exercise performance. Most of these aids are ineffective.
1.0
1.1 Nutrition is defined as the “science of food; the nutrients and the substances therein; their action, interaction, and balance in relation to health and disease; and the process by which the organism (e.g., human body) ingests, digests, absorbs, transports, utilizes, and excretes food substances.” Nutrients are substances essential for health that the body cannot
make or makes in quantities too small to support health. Nutrients primarily provide energy, support growth and development, and/or keep body functions running smoothly. Carbohydrates, proteins, lipids, and water are macronutrients. Vitamins and minerals are micronutrients. Phytochemicals are plant components and zoochemicals are components in animals that may provide significant health benefits.
1.2 Humans obtain the energy needed to perform body functions and do work from carbohydrates, fats, and proteins. Alcohol also provides energy but is not considered an essential nutrient. A kilocalorie is the amount of heat energy it takes to raise the temperature of 1000 g (1 liter) of water 1°C. The physiological fuel values are 4, 9, 4, and 7 for carbohydrate, fat, protein, and alcohol, respectively.
1.3 North American adults consume, on average, 16% of
their energy intake as proteins, 50% as carbohydrates, and 33% as fats. Animal sources, such as meat, seafood, dairy products, and eggs, are the main protein sources for North Americans. About half the carbohydrate in North American diets comes from simple carbohydrates; the other half comes from starches. Many North Americans are consuming more saturated fat, cholesterol, and sodium and less vitamin A, vitamin E, iron, and calcium than recommended. Daily food intake satisfies hunger (physical need for food) and social and emotional needs. Appetite and food choice depend on many factors.
1.4 Nutritional health is determined by the sum of the status of each nutrient. Optimal, or desirable, nutritional status for
a nutrient is the state in which body tissues have enough
of the nutrient to support normal functions and to build and maintain surplus stores. Undernutrition occurs when nutrient intake does not meet needs, causing surplus stores to be used. The consumption of more nutrients than needed leads to overnutrition. Healthy People 2010 set health promotion and disease prevention goals, many of which promote desirable nutrition that supports healthful lifestyles and reduces preventable death and disability. A nutritional assessment considers background factors, as well as anthropometric, biochemical, clinical, dietary, and environmental assessments.
1.5 Genetic endowment affects almost every medical condition. Genes direct the growth, development, and maintenance
of cells and, ultimately, of the entire organism. Most chronic nutrition-related diseases are influenced by genetic, nutritional, and lifestyle factors. Although some individuals may be genetically predisposed to chronic disease, the actual development of the disease depends on lifestyle and environmental factors. Scientists are currently developing therapies to correct some genetic disorders. Experts recommend that anyone considering genetic testing first undergo genetic counseling.
1.6 Research that creates the foundation for nutrition has developed through the use of the scientific method. To test hypotheses and eliminat coincidental or erroneous hypotheses, scientists perform controlled experiments. The te e scientific method requires an open, curious mind and a questioning, skeptical attitude. Scientists m mu ar us re s es t tn su no up o accept hypotheses until they t y a p t p p by considerable research evi d i c theories, laws, and discoveries always should be subjected to challenge and change. Experimental approaches used to test research hypotheses in humans include migrant, cohort, case-control, and blinded studies. Once an experiment is complete, scientists summarize the findings and seek to publish the results in a scientific, peer-reviewed journal. The objective of peer review is to ensure that only the most unbiased, objective findings from carefully designed and executed research studies are published.
1.7 Nutrition claims often appear in media stories and
in advertisements. It can be difficult to discern
whether the claims are true. A cautious approach to nutrition-related claims and products is important.
The Dietary Supplement Health and Education Act classified vitamins, minerals, amino acids, and herbal remedies as “foods,” effectively restraining the FDA
from regulating them as rigorously as food additives and drugs. When selecting nutrition-related products, carefully scrutinize product labels. For those who feel they need
to improve their diet and health, a safe approach is to consult a physician or registered dietitian before purchasing dietary supplements.
2.0
2.1 The Dietary Reference Intakes (DRIs) differ by life stage and include Estimated Average Requirements (EARs), Recommended Dietary Allowances (RDAs), Adequate Intakes (AIs), Tolerable Upper Intake Levels (Upper Levels, or ULs), and Estimated Energy Requirements (EERs). EARs are daily nutrient intake amounts estimated to meet the needs of half of the people in a life stage. EARs are set only if a method exists for accurately measuring whether intake is adequate. RDAs are daily nutrient intake amounts sufficient to meet the needs of nearly all individuals (97
to 98%) in a life stage. RDAs are based on a multiple of
the EAR. AIs are daily intake amounts set for nutrients
for which there are insufficient data to establish an EAR. AIs should cover the needs of virtually all individuals in
a specific life stage. ULs are the maximum daily intake amount of a nutrient that is not likely to cause adverse health effects in almost everyone. EERs are average daily energy needs. For each macronutrient, the Adequate Macronutrient Distribution Ranges (AMDRs) provide a range of recommended intake, as a percent of energy. DRIs are intended mainly for diet planning. Nutrient density is a tool for assessing the nutritional quality of individual foods.
2.2 Daily Values (DVs) are generic standards developed by the FDA for Nutrition Facts panels. DVs are based on Reference Daily Intakes and Daily Reference Values. Nutrition Facts panels present information for a single serving of food using serving sizes specified by the FDA. These components must be listed on most Nutrition Facts panels: total calories (kcal), calories from fat, total fat, saturated fat, trans fat, cholesterol, sodium, total carbohydrate, fiber, sugars, protein, vitamin A, vitamin C, calcium, and iron. Food labels may include nutrient content claims, health claims, preliminary health claims, and structure/function claims.
2.3 Nutrient databases make it possible to estimate quickly
the amount of calories and many nutrients in the foods
we eat. The data in nutrient databases are the results of thousands of analytical chemistry studies. Nutrient values in the nutrient databases are average amounts found in the analyzed samples of the food. It is wise to view nutrient composition databases as tools that approximate nutrient intake, rather than precise measurements. Energy density is determined by comparing a food’s calorie content with the weight of food.
2.4 The Dietary Guidelines are the foundation of the U.S. government’s nutrition policy and education. They reflect what experts believe is the most accurate and up-to-
date scientific knowledge about nutritious diets, physical activity, and related lifestyle choices. Dietary Guideline recommendations are grouped into 9 topics: adequate nutrients within energy, weight management, physical activity, food groups to encourage, fats, carbohydrates, sodium and potassium, alcoholic beverages, and food safety.
2.5 The goal of MyPyramid, Steps to a Healthier You, is to provide advice that helps consumers live longer, better, and healthier lives. MyPyramid was designed to depict elements that form the basis of a healthy diet and lifestyle: variety, proportionality, moderation, personalization, physical activity, and gradual improvement. The nutritional adequacy of diets planned using MyPyramid depend on selecting a variety of foods, including grains, vegetables, fruits, milk, meat and beans, and oils. A balanced diet includes foods from every food group in the recommended amounts. Variety means eating many different foods from each food group. Moderation means keeping portions sizes under control
3.1
3.1 Food insecurity and hunger occur in virtually every country. About 1 in 8 people worldwide do not get enough food
to meet their requirements. Food insecurity is linked to poverty. Food insecure people tend to have poorer diets
and suffer more health problems. Children without enough food do not grow normally and are more likely to suffer diseases and death. In the U.S., the USDA monitors food insecurity. About 11% of U.S. households are food insecure, with a third of these having very low food security. The Food Stamp Program is the most important food assistance program offered by the U.S. government. Other programs include WIC and the National School Lunch and Breakfast Programs. Emergency food programs also play an important role for food insecure people.
3.2 Organic foods are grown in ways that promote healthy soils, waterways, crops, and animals. Many substances
and processes cannot be applied to organic foods. The USDA certifies foods as organic. Organic foods contain fewer pesticides but their nutritional value may not differ from conventionally grown food. Genetically modified (GM) foods have new or modified genes to produce a plant, an animal, or another organism with a new trait. The most common GM foods in the U.S. are soybeans, corn, and cotton altered either to be herbicide resistant or to produce their own pesticides. Other GM applications are used to increase milk production and to produce chymosin for cheese making. GM foods are regulated by the FDA, USDA, and EPA. Labeling of GM foods is not required. Many concerns have been voiced about GM foods, including the safety of these foods for people and the environment.
3.3 Food spoilage results from microorganism and enzyme action. Food preservation methods stop or slow the rate
of spoilage. Food irradiation is approved for some foods. Irradiated foods are not radioactive. Food additives are regulated by the FDA. Some food additives are considered GRAS and have not had formal testing. New food additives must be carefully tested by the manufacturer and evaluated by the FDA. Over 3000 food additives are approved for use in the U.S. Intentional food additives are used for a specific purpose, whereas incidental food additives become a part
of food because of some aspect of production. Some people are concerned about the safety of food additives; however, no evidence shows that limiting additives will make you healthier. To lower your intake of additives, read food labels and eat fewer highly processed foods.
3.4 Foodborne pathogens are a significant cause of illness and death in the U.S. People more at risk are infants, children, the elderly, people with certain diseases, pregnant women, and those who have weakened immune systems. Foodborne illness usually causes gastrointestinal effects, but it can have more serious lasting effects. Over 250 pathogens, including viruses, bacteria, parasites, and toxins, can cause foodborne illness, but most are caused by bacteria (Salmonella, Campylobacter, and E. coli) and viruses. Meats, poultry, eggs, shellfish, dairy products, and fresh produce are often implicated in outbreaks of foodborne illness. Public water supplies are regulated by the EPA and municipal water systems. Bottled water is regulated by the FDA. There are numerous threats to safe water, but water contamination that poses a danger to health is rare.
3.5 Several government agencies, including the USDA, FDA, and CDC, are responsible for coordinating food safety efforts, but everyone has a responsibility�fo�r �keeping food safe to eat. The risk of foodborne illness can be reduced
by using good personal and kitchen hygiene, handling food safely, and avoiding foods that present extra risk. Washing hands, preventing cross-contamination, washing produce, keeping foods out of danger zone temperatures, and cooking meat, poultry, eggs, fish, and casseroles to
the safe temperatures are especially important. Cooked foods should be either consumed right away or refrigerated within 2 hours. Traveler’s diarrhea is common in visitors
to developing countries. Following guidelines about water and produce consumption can help reduce the likelihood of contracting it.
3.6 Environmental contaminants in food include lead, mercury, industrial contaminants (e.g., dioxins and polychlorinated biphenyls [PCBs]), and pesticides. Lead can damage the developing nervous system; children are most at risk. Iron- deficient children may be at more risk of lead toxicity. Dioxins can contaminate food, especially fish. They are carcinogens and cause liver and nerve damage. Mercury also is found in fish, especially shark, swordfish, king mackerel, and tilefish. The FDA and EPA recommend that children and pregnant and breastfeeding women limit their exposure to high- mercury fish. PCBs can be found in fish, too. Farmers use pesticides to increase agricultural productivity. Pesticides are regulated by the EPA, USDA, and FDA. Pesticides in foods are a special concern for young children. The widespread use of antibiotics in animal feed is a concern because they foster the growth of antibiotic-resistant bacteria.
4.0
4.1 The cell is the basic structural unit of the human body.
Cells join together to make up tissues. The 4 primary types of tissues are epithelial, connective, muscle, and nervous. Tissues unite to form organs and organs work together as an organ system.
4.2 The gastrointestinal (GI) tract includes the mouth, esophagus, stomach, small intestine, and large intestine (colon, rectum, and anus). Sphincters along the GI tract control the flow of digesting food. The accessory organs (liver, gallbladder, and pancreas) are an important part of the digestive system. Movement through the GI tract is mainly through muscular contractions known as peristalsis. GI contents are mixed with segmental contractions. Enzymes are specialized protein molecules that speed up digestion
by catalyzing chemical reactions. Most digestive enzymes are synthesized in the small intestine and pancreas. A lack of digestive enzymes can result in poor digestion, poor absorption, malnutrition, and weight loss.
- 3 The mouth chews food to break it into smaller parts and increase its surface area, which enhances enzyme activity. Amylase produced by salivary glands digests a small amount of starch. Chewed food mixed with saliva is called a bolus. When swallowing is initiated, the epiglottis covers the trachea to prevent food from entering it. Peristalsis moves food down the esophagus. There are 5 basic taste sensations perceived by taste cells found on taste buds in the mouth, especially the tongue. Genetic variability affects the ability to taste bitter compounds. The sense of smell contributes greatly to flavor perceptions.
- 4 The lower esophageal sphincter protects the esophagus from the backflow of acidic stomach contents. When this sphincter does not work normally, heartburn and GERD may occur. Stomach cells produce gastric juice (HCl, pepsinogen, mucus, and intrinsic factor). Pepsin (from pepsinogen) starts the digestion of protein. Mixing of food and gastric juice results in the production of chyme, the liquid substance released in small amounts into the small intestine.
4.5 The small intestine has 3 sections: duodenum, jejunum, and ileum. Most digestion occurs in the small intestine. Secretions from the liver, gallbladder, and pancreas are released into the small intestine. These secretions contain enzymes, bile, and sodium bicarbonate. Villi in the small intestine greatly increase its surface area, which enhances absorption. Villi are lined by enterocytes that release enzymes. Enterocytes are constantly broken down and replaced. Diseases, such as celiac disease, damage the villi and enterocytes. The liver, gallbladder, and pancreas aid digestion and absorption. The liver produces bile, which is stored y contain the alkaline sodium bicarbonate and digestive d in the gallbladder and used to oe e m mu u l ls si i f fy f fa a t t. . P P a a n nc c r re e a at t i i c c j ju ui ic ce e s s enzymes. Bile and pancreatic juice are released into the small intestine via the pancreatic bile duct. Most nutrients are absorbed primarily in the small intestine. There are 4 main types of absorption: passive diffusion, facilitated diffusion, active absorption, and endocytosis. Hormones regulate digestion and absorption. The 4 major GI- regulating hormones are gastrin, cholecystokinin, secretin, and gastric inhibitory peptide.
4.6 Nutrients absorbed into the absorptive cells are transported in the body via either the cardiovascular or the lymphatic circulation. Water-soluble nutrients entering the cardiovascular system from absorptive cells travel via the portal vein to the liver, then to the general circulation
and body tissues. Fat-soluble and large particles enter the lymphatic system from absorptive cells. Lymphatic vessels drain into the thoracic duct that releases its contents to the bloodstream.
4.7 The large intestine is the last part of the GI tract. It houses many species of beneficial and pathogenic bacteria, absorbs water and electrolytes, and forms and eliminates feces. GI contents entering the large intestine are mainly water, some minerals, fiber, and some starch. Carbohydrates (fiber and starch) can be digested to some extent by bacteria in the large intestine and form short-chain fatty acids, which serve as an energy source for the large intestine and may help prevent and treat diseases. Bacteria in the large intestine also produce intestinal gas. Probiotics are live microorganisms found in fermented foods and supplements. They may promote intestinal health, such as preventing diarrhea
in children. Prebiotics are nondigestible carbohydrates that promote the growth of beneficial bacteria in the large intestine. It takes 12 to 24 hours for contents to pass through the large intestine. Feces defecated through
4.8
the rectum contain about 75% water and 25% solids— indigestible plant fibers, tough connective tissues from animal foods, and bacteria.
Common digestive disorders include heartburn, GERD, peptic ulcers, gallstones, constipation, diarrhea, irritable bowel syndrome, and hemorrhoids. These disorders often can be prevented or treated with healthy nutrition and lifestyle habits.
5.0
5.1 The general formula for carbohydrates is (CH2O)n,
where n represents the number of times the ratio is repeated. The common monosaccharides are glucose, fructose, and galactose. Sugar alcohols are derivatives of monosaccharides. Additional monosaccharides found in nature are ribose and deoxyribose. Carbohydrates containing 2 monosaccharides are called disaccharides. Disaccharides include maltose, sucrose, and lactose. Oligosaccharides are complex carbohydrates that contain 3 to 10 single sugar units. Polysaccharides are complex carbohydrates that
often contain hundreds to thousands of glucose molecules. Digestible polysaccharides are starch and glycogen. Dietary and functional fibers are indigestible polysaccharides.
5.2 Carbohydrates are found in a wide variety of foods, including table sugar, jam, jelly, fruits, soft drinks, rice, pasta, cereals, breads, dried beans, lentils, corn, peas, and dairy products. Starches contribute much of the carbohydrate
in our diets. A diet rich in grains, legumes, and tubers also can provide significant amounts of dietary fiber (especially insoluble cellulose, hemicellulose, and lignins). Substances that impart sweetness to foods fall into 2 broad classes: nutritive sweeteners, which can be metabolized to yield energy, and alternative sweeteners, which provide no food energy. The sugar alcohols, sorbitol, mannitol, and xylitol, are nutritive sweeteners used in sugarless gum and candies. Alternative (or artificial or non-nutritive) sweeteners provide non-caloric or very-low-calorie sugar substitutes.
5.3 Adults need about 130 g/day of digestible carbohydrate to supply adequate glucose for the brain and central nervous system, without having to rely on partial replacement of glucose by ketone bodies as an energy source. In North America, carbohydrates supply about 50% of energy intakes in adults. The Dietary Guidelines for Americans recommend limiting added sugars to approximately 6% of total energy intake. The Institute of Medicine’s Food and Nutrition Board set an upper limit of 25% of energy intake for added sugar consumption. The Adequate Intake for fiber is based on a goal of 14 g/1000 kcal consumed. For adults up to age 50 years, the Adequate Intake is set at 25 g for women and 38 g for men. After age 50, the Adequate Intake falls
to 21 g/day and 30 g/day, respectively. In North America, carbohydrates supply about 50% of the energy intakes of adults. Sugar intake tends to be higher than recommended and fiber intake lower than recommended.
5.4 Most of the digestible carbohydrates in our diets are broken down to glucose. As glucose, they provide a primary source of energy, spare protein for vital processes, and prevent ketosis. Fiber helps prevent constipation and diverticular disease and enhances the management of body weight, blood glucose levels, and blood cholesterol levels.
5.5 During digestion, starch and sugars are broken into monosaccharide units that are small enough to be absorbed. The enzymatic digestion of some carbohydrates begins in the mouth with the action of an enzyme called salivary amylase. Salivary enzyme is inactivated by the acidity of the stomach.
In the small intestine, polysaccharides are digested further by pancreatic amylase and specialized enzymes in the absorptive cells of the small intestine. Glucose and galactose are absorbed by an active absorption process. Fructose is taken up by the absorptive cells via facilitated diffusion. Monosaccharides are transported via the portal vein to the liver. Within the liver, fructose and galactose are converted to glucose. Glucose is transported through the bloodstream for use by the cells of the body.
5.6 Adequate carbohydrate intake is important for maintaining health
and decreasing the risk of chronic disease. Very high intakes of fiber (i.e., above 50 to 60 g/day) combined with low fluid intake can result in hard, dry stools that are painful to eliminate. Very high fiber intakes also may decrease the absorption of minerals. High intakes of sugars can displace more nutritious foods and increase the risk of
weight gain, obesity, and dental
caries. Lactose intolerance can cause
symptoms of abdominal pain, bloating, gas, and diarrhea
after consuming lactose, especially in large amounts. An inability to regulate glucose metabolism can result in diabetes. The major forms of diabetes are type 1 diabetes and type
2 diabetes. Type 1 diabetes often begins in late childhood and runs in families, suggesting a genetic link. The onset
of type 1 diabetes is caused by insufficient insulin release by the pancreas, which results in increased blood glucose levels. Type 1 diabetes is treated by insulin and diet therapy. Poorly controlled diabetes can cause blindness, cardiovascular disease, kidney disease, and nerve deterioration. A person with diabetes should work regularly with a physician and dietitian to monitor and adjust diet, medications, and physical activity. Type 2 diabetes is a progressive disease characterized by insulin resistance or loss of responsiveness by body cells to insulin. As a result, glucose is not readily transferred into cells and builds up in the bloodstream, causing hyperglycemia. Treatments for type 2 diabetes
are aimed at maintaining normal ranges of blood glucose through lifestyle modification and medication use. Glycemic index is a ratio of the blood glucose response of a given food, compared with a standard, such as white bread. Glycemic load takes into account the glycemic index and the amount of carbohydrate consumed.
6.0
6.1 Triglycerides are the most common type of lipid found in foods and in the body. Each triglyceride molecule consists of 3 fatty acids attached to a glycerol. A triglyceride that loses a fatty acid is a diglyceride. A monoglyceride results when 2 fatty acids are lost. The carbon chains of fatty acids can vary in 3 ways: the number of carbons in the chain, the extent to which the chain is saturated with hydrogen, and the shape of the chain (straight or bent). Hydrogenation adds hydrogen to the carbon chain of unsaturated fats. The systems commonly used to name fatty acids, omega and delta, are based on the numbers of carbon atoms and the location of double bonds in a fatty acid’s carbon chain. Essential fatty acids (alpha-linolenic acid and linoleic acid) must be obtained from the diet because humans cannot synthesize them.
6.2 Triglycerides are the main fuel source for all body cells, except the nervous system and red blood cells. Triglycerides are
the body’s main storage form of energy. The insulating layer of fat just beneath the skin is made mostly of triglycerides. Fats in food carry fat-soluble vitamins (vitamins A, D, E,
and K) to the small intestine. Essential fatty acids, along
with phospholipids and cholesterol, are important structural components of cell walls. They also keep the cell wall fluid and flexible, so that substances can flow into and out of the cell. Eicosanoids, which are made from essential fatty acids, have over 100 different actions, such as regulating blood pressure, blood clotting, sleep/wake cycles, and body temperature.
6.3 Almost all foods provide at least some triglycerides. Most triglyceride-rich foods contain a mixture of fatty acids. The fat in some foods is visible; however, fat is hidden in many foods. Fat replacements help consumers trim fat intake and still enjoy the mouthfeel sensations fat provides.
6.4 The structure of phospholipids is very similar to that
of triglycerides, except a fatty acid is replaced with a compound that contains the mineral phosphorus and often has nitrogen attached. Phospholipids function in a watery environment without clumping together. The hydrophilic head of phosphate is attracted to water, and the fatty acid
tail of phospholipids is attracted to fats. When placed in water, phospholipids cluster together, with their hydrophilic phosphate heads facing outward in contact with water and their hydrophobic tails extending into the cluster away from the water. In the body, phospholipids have 2 major roles: cell membranecomponentandemulsifier.Phospholipidscanbe synthesized by the body or supplied by the diet.
- 5 The carbons in the structure of sterols are mostly arranged in many rings. Cholesterol, the most well-known sterol, is used in the body to make bile and steroid hormones, such as testosterone, estrogens, the active form of vitamin D hormone, and corticosteroids. Cholesterol is found in foods of animal origin, such as meat, fish, poultry, eggs, and dairy products. Foods of plant origin do not contain cholesterol.
- 6 The Adequate Macronutrient Distribution Range for total fat is 20 to 35% of calories for most age groups. Saturated fat intake, including trans fats, and cholesterol should be kept as low as possible while still consuming a nutritionally adequate diet. Cholesterol intake should be limited to about 300 mg daily. Fat intake recommendations are lower for those at risk of heart disease. Adequate Intakes for essential fatty acids equal less than 120 calories daily for women and 170 calories for men—that’s about 2 to 4 tablespoons daily of oils rich in these fatty acids. Most North Americans get too much saturated and too little monounsaturated and polyunsaturated fat. Omega-6 fatty acid intake is usually plentiful, but omega-3 intakes often are lower than optimal.
6.7 Fat digestion occurs mostly in the small intestine. The presence of fat in the small intestine triggers the release
of cholecystokinin from intestinal cells. Cholecystokinin stimulates the release of bile and pancreatic enzymes. Bile emulsifies fats and allows enzymes to efficiently break triglycerides into monoglycerides and free fatty acids. Phospholipids and cholesterol are digested mostly in the small intestine. After absorption, short and medium chain fatty acids mostly enter the circulatory system. Long chain fatty acids enter the lymphatic circulation.
6.8 Fats are transported in the blood as lipoproteins called chylomicrons, very-low-density lipoproteins (VLDLs), intermediate-density lipoproteins (IDLs), low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs). Lipoproteins have a core, made of lipids, that is covered with a shell composed of protein, phospholipid, and cholesterol. The shell lets the lipoprotein circulate in the blood. The receptor pathway for cholesterol uptake removes LDL from the blood, breaks it down, and uses the component parts for maintaining the cell membrane or synthesizing compounds. Oxidized LDL
is removed from the blood by the scavenger pathway for cholesterol uptake. Over time, cholesterol builds up in the scavenger cells. When scavenger cells have collected and deposited cholesterol for many years at a heavy pace, cholesterol builds up on the inner blood vessel walls and plaque develops. HDL roams the bloodstream, picking up cholesterol from dying cells and other sources,
and donates the cholesterol to other lipoproteins for transport back to the liver to be excreted.
6.9 Intakesofpolyunsaturatedfatsgreaterthan10%oftotalcalorie intake seem to increase the amount of cholesterol deposited
in arteries. Diets that include fish rich in omega-3 twice a
week can reduce blood clotting abilities and may favorably affect heart rhythm. Omega-6 and omega-3 fatty acids use
the same metabolic pathways; as a result, imbalances in intake of these fatty acids may cause health problems. Rancid fats contain compounds that can damage cells. Trans fatty acids raise blood cholesterol levels, lower HDL cholesterol levels, and increase inflammation in the body. Diets high in total fat increase the risk of obesity; colon, prostate, and breast cancer; and cardiovascular disease (CVD). Atherosclerotic plaque is probably first deposited to repair injuries in the lining in any artery. As atherosclerosis progresses, plaque thickens over time, causing arteries to harden, narrow, and become less
elastic. CVD risk factors are age, gender, genetics, race, blood cholesterol levels, blood triglyceride levels, hypertension, smoking, physical inactivity, obesity, and diabetes. All adults age 20 years or older should have a blood lipoprotein profile done every 5 years. Lifestyle changes can lower blood LDL cholesterol levels and reduce health risks.
7.0
7.1 Amino acids, the building blocks of proteins, contain a usable form of nitrogen for humans. Of the 20 amino-acids needed by the body, 9 must be provided in the diet (essential). The other 11 can be synthesized by the body (nonessential) from amino acids in the body’s amino acid pool. High-quality, also called complete, proteins contain ample amounts of all 9 essential amino acids. Foods derived from animal sources provide high-quality, or complete, protein. Lower-quality, or incomplete, proteins lack sufficient amounts of 1 or more essential amino acids. This is typical of plant foods. Different types of plant foods eaten together often complement each other’s amino acid deficits, thereby providing high-quality protein in the diet.
7.2 Individualaminoacidsarelinkedtogethertoformproteins. The sequential order of amino acids determines the protein’s ultimate shape and function. This order is directed by DNA
in the cell nucleus. Diseases, such as sickle-cell anemia, can occur if the amino acids are incorrect in a polypeptide chain. When the 3-dimensional shape of the protein is unfolded— denatured—by treatment with heat, acid, or alkaline solutions, or other processes, the protein also loses its biological activity.
7.3 Almost all animal products are rich sources of protein. The high quality of these proteins means that they can be easily converted into body proteins. Legumes, nuts, seeds, and grains are good sources of plant protein. Protein quality can be measured by determining the extent to which the body can retain the nitrogen contained in the amino acids absorbed. This is called biological value. In addition, the balance of essential amino acids in a food can be compared with an ideal pattern to determine chemical score. When multiplied by the degree of digestibility, the chemical score yields the Protein Digestibility Corrected Amino Acid Score (PDCAAS).
7.4 The adult RDA for protein is 0.8 g per kg of healthy body weight. For a typical 154-lb (70-kg) person, this corresponds to 56 g of protein daily; for a 125-lb (57-kg) person, this corresponds to 46 g/day. The North American diet generally supplies plenty of protein: men typically consume about
100 g of protein daily, and women consume about 65 g. These intakes are also of sufficient quality to support body functions.
7.5 Protein digestion begins in the stomach, where proteins are broken down into shorter polypeptide chains of amino acids. In the small intestine, these polypeptide chains are digested into dipeptides and amino acids, which are absorbed by the small intestine, where any remaining peptides are broken down into amino acids. Absorbed amino acids then travel via the portal vein to the liver.
7.6 Important body components—such as muscles, connective tissue, transport proteins, enzymes, hormones, and antibodies—are made of proteins. Proteins also provide carbon skeletons, which can be used to synthesize glucose when necessary.
7.7 Undernutrition can lead to protein-energy malnutrition in the form of kwashiorkor or marasmus. Kwashiorkor results primarily from an inadequate energy intake with a severe protein deficit, often accompanied by disease and infection. Kwashiorkor frequently occurs when a child is weaned from human milk and fed mostly starchy gruels. Marasmus results from extreme starvation—a negligible intake of both protein and energy. Marasmus commonly occurs during famine, especially in infants. These conditions have been noted in some North Americans with cancer, AIDS, malabsorption disease, anorexia nervosa, alcoholism, or limited income and resources to obtain food. High-protein diets (above 35%
of energy intake) do not provide additional health benefit. They are associated with dehydration, overburdening of the kidneys’ capacity to excrete nitrogen wastes, increased risk of cardiovascular disease and certain cancers, increased urinary calcium loss, and risk of amino acid imbalance and toxicity.
7.8 Food allergies involve immune system responses designed
to eliminate allergens that the body mistakenly reacts to as though they were harmful invaders. Symptoms range from mild to life-threatening. The only way to prevent reactions is to avoid foods known to trigger allergic reactions.
7.9 Vegetarian diets are becoming more popular as individuals recognize the possible health benefits of plant-based diets. Low intakes of riboflavin, vitamins D and B-12, calcium, iron, and zinc are of greatest concern in vegetarian diets. Vegetarian diets require knowledge and creative planning to obtain high-quality protein and other key nutrients
but can be nutritionally adequate when guidelines are followed.
9.0
9.1 Metabolism refers to the entire network of chemical processes involved in maintaining life. It encompasses
all the sequences of chemical reactions that occur in the body. Some of these biochemical reactions enable us to release and use energy from carbohydrate, fat, protein,
and alcohol. Metabolism is the sum total of all anabolic
and catabolic reactions. A molecule of ATP consists of the organic compound adenosine (comprised of the nucleotide adenine and the sugar ribose) bound to 3 phosphate groups. ATP is the energy currency for the body. As ATP is broken
down to ADP plus Pi, energy is released from the broken bond. Every cell contains catabolic pathways, which release energy to allow ADP to combine with Pi to form ATP. The synthesis of ATP from ADP and Pi involves the transfer of energy from energy-yielding compounds (carbohydrate, fat, protein, and alcohol). This process uses oxidation-reduction reactions, in which electrons (along with hydrogen ions) are transferred in a series of reactions from energy-yielding compounds eventually to oxygen. The process of cellular respiration oxidizes (removes electrons) to obtain energy (ATP). Oxygen is the final electron acceptor. When oxygen is readily available, cellular respiration may be aerobic. When oxygen is not present, anaerobic pathways are used.
9.2 Glucose metabolism begins with glycolysis, which literally means “breaking down glucose.” Glycolysis has 2 roles: to break down carbohydrates to generate energy and to provide building blocks for synthesizing other needed compounds. During glycolysis, glucose passes through several steps, which convert it to 2 units of a 3-carbon compound called pyruvate. Glycolysis nets 2 ATP. Pyruvate passes from the cytosol into the mitochondria, where the enzyme pyruvate dehydrogenase converts pyruvate into the compound acetyl-CoA in a process called a transition reaction. Acetyl-CoA molecules enter the citric acid cycle, which is a series of chemical reactions that convert carbons in the acetyl group to carbon dioxide while harvesting energy to produce ATP. In the citric acid cycle, acetyl-CoA undergoes many metabolic conversions, which result in the production of GTP, ATP, NADH, and FADH2. NADH and FADH2 enter the electron transport chain, which passes electrons along a series of electron carriers. As electrons pass from one carrier to the next, small amounts of energy are released. This metabolic process is called oxidative phosphorylation, and it is the pathway in which energy derived from glycolysis, the transition reaction, and the citric acid cycle is transferred to ADP + Pi to form ATP and water.
9.3 The first step in generating energy from a fatty acid is to cleave the carbons, 2 at a time, and convert the 2-carbon fragments to acetyl-CoA. The process of converting a free fatty acid to multiple acetyl-CoA molecules is called beta- oxidation, because it begins with the beta carbon, which is the second carbon on a fatty acid chain. Fatty acids
can be oxidized for energy but cannot be converted into glucose. During low carbohydrate intakes and uncontrolled diabetes, more acetyl-CoA is produced in the liver than can be metabolized. This excess acetyl-CoA is synthesized into ketone bodies, which can be used as an energy source by other tissues or excreted in the urine and breath.
9.4 Protein metabolism begins after proteins are degraded into amino acids. To use an amino acid for fuel, cells must first deaminate them (remove the amino group, NH2). Resulting carbon skeletons mostly enter the citric acid cycle. Some carbon skeletons also yield acetyl-CoA or pyruvate. The process of generating glucose from amino acids is called gluconeogenesis. Acetyl-CoA molecules cannot participate in gluconeogenesis; thus, ketogenic amino acids cannot participate in gluconeogenesis.
9.5 The alcohol dehydrogenase (ADH) pathway is the main pathway for alcohol metabolism. Alcohol is converted
in the cytosol to acetaldehyde by the action of the enzyme alcohol dehydrogenase and the coenzyme NAD+. NAD+ picks up 2 hydrogen ions and 2 electrons from
the alcohol to form NADH + H+ and produces the intermediate acetaldehyde. Acetaldehyde is converted to acetyl-CoA, again yielding NADH + H+ with the aid of the enzyme aldehyde dehydrogenase and coenzyme A. Most of the acetyl-CoA is used to synthesize fatty acids and triglycerides, resulting in the accumulation of fat
in the liver. When an individual consumes too much alcohol, a second pathway—called
the microsomal ethanol oxidizing
system (MEOS)—is activated
to help metabolize the excess alcohol.
9.6 The liver plays the major role in regulating metabolism. Additional means of regulating metabolism involve enzymes, ATP concentrations, and minerals. Many micronutrients (thiamin, niacin, riboflavin, biotin, pantothenic acid, vitamin B-6, magnesium, iron, and copper) play important roles in the metabolic pathway.
9.7 During fasting, the body breaks down
both amino acids and fats for energy. The
body undergoes a series of adaptations that
prolong survival. One of these adaptations is
the slowing of metabolic rate and the reduction in energy requirements. This helps slow the breakdown of lean tissue to supply amino acids for gluconeogenesis. Another adaptation allows the nervous system to use less glucose and more ketone bodies. Fat consumed in excess of need goes into storage in adipose cells. Compared with the conversion of carbohydrate and protein, relatively little energy is required to convert dietary fat into body fat. Therefore, high-fat diets promote the accumulation of body fat. Inborn errors of metabolism occur when a person inherits a defective gene coding for a specific enzyme from one or both parents. Some of the most common inborn errors of metabolism are phenylketonuria (PKU), galactosemia, and glycogen storage disease. Strict diets can help those with these inborn errors of metabolism minimize many of the serious effects of these diseases.
10.0
10.1 Energy balance considers energy intake and energy output. Negative energy balance occurs when energy output surpasses energy intake, resulting in weight loss. Positive energy balance occurs when energy intake is greater than output, resulting in weight gain. Basal metabolism, the thermic effect of food, physical activity, and thermogenesis account for total energy use by the body. Basal metabolism, which represents the minimum amount of energy used to keep the resting, awake body alive, is primarily affected by lean body mass, body surface area, and thyroid hormone concentrations. Physical activity is energy use above the amount expended when at rest. The thermic effect of
food describes the increase in metabolism that facilitates digestion, absorption, and processing of nutrients recently consumed. Thermogenesis is heat production caused
by shivering when cold, fidgeting, and other stimuli. In
a sedentary person, about 70 to 80% of energy use is accounted for by basal metabolism and the thermic effect of food.
10.2 Direct calorimetry estimates energy expenditure by measuring the amount of body heat released by a person. Indirect calorimetry, the most commonly used method
to determine energy use by the body, involves collecting expired air from an individual during a specified amount of
time. This method works because a predictable relationship exists between the body’s use of energy and the amount
of oxygen consumed and carbon dioxide produced. Estimated Energy Requirements (EERs) are based on formulas developed by the Food and Nutrition Board
that can be used to estimate energy needs.
- 3 Groups of cells in the hypothalamus and other regions in the brain affect hunger, the primarily internal desire to find and eat food. These cells monitor macronutrients and other substances in the blood and read low amounts as a signal to promote feeding. A variety of external (appetite- related) forces, such as food availability, affect satiety. Hunger cues combine with appetite cues to promote feeding. Numerous factors elicit satiety, such as flavor, smell, chewing, and the effects of digestion, absorption, and metabolism.
- 4 A person of healthy weight generally shows good health and performs daily activities without weight-related problems. A body mass index (weight in kilograms/ height2 in meters) of 18.5 to 25 is one measure of healthy weight, although weight in excess of this value may not lead to ill health. A healthy weight is best determined in conjunction with a thorough health evaluation by a health-care provider. A body mass index of 25 to 29.9 represents overweight. Obesity is defined as a total body fat percentage over 25% (men) or 35% (women), or a body mass index of 30 or more. Fat distribution greatly determines health risks from obesity. Upper-body fat storage, as measured by a waist circumference greater than 40 inches (102 cm) (men) or 35 inches (88 cm) (women), increases the risks of hypertension, cardiovascular disease, and type 2 diabetes more than does lower-body fat storage.
10.5 Research suggests that genes account for up to 40 to 70% of weight differences between people. The genes may be those that determine body type, metabolic rate, and the factors that affect hunger and satiety. Some individuals are thought to have a genetic predisposition to obesity because they inherit a thrifty metabolism. The set-point theory proposes that humans have a genetically predetermined body weight or body fat content, which the body closely regulates. Environmental factors have important effects
on what we eat. These factors may define when eating is appropriate, what is preferable to eat, and how much food should be eaten. Even though our genetic backgrounds have a strong influence on body weight and composition, genes are not destiny—both nature and nurture are involved.
10.6 A sound weight-loss program emphasizes a wide variety of low-energy-density foods; adapts to the dieter’s habits; consists of readily obtainable foods; strives to change poor eating habits; stresses regular physical activity; and stipulates the participation of a physician if weight is to be lost rapidly or if the person is over the age of 40 (men) or 50 (women) years and plans to perform substantially greater physical activity than usual. A pound of adipose tissue contains about 3500 kcal. Thus, if energy output exceeds intake by about 500 kcal per day, a pound of adipose tissue can be lost per week. Physical activity as part of a weight-loss program should be focused on duration, rather than intensity. Behavior modification is a vital part of a weight-loss program because the dieter may have many habits that discourage weight maintenance.
10.7 Many fad diets promise rapid weight loss; however, these diets are not designed for permanent weight loss. Low- carbohydrate diets work in the short run because they limit total food intake; however, long-term studies have shown that the weight generally returns in about a year. Weight- loss drugs are reserved for those who are obese or have weight-related problems, and they should be administered under close physician supervision. The treatments for severe obesity include surgery to reduce stomach volume to approximately 1 oz (30 ml) and very-low-calorie diets containing 400 to 800 kcal/day. Both of these measures should be reserved for people who have failed at more
conservative approaches to weight loss. They also require close medical supervision. Underweight can be caused by a variety of factors, such as excessive physical activity and genetic background. Sometimes
being underweight requires medical attention. A physician should be consulted first to rule out underlying disease. The underweight person may need to increase portion sizes and include energy-dense foods in
the diet.
10.8 Anorexia nervosa usually starts with dieting in early puberty and proceeds to the near-total refusal to eat. Early warning signs include intense concern about weight gain and dieting, as well as abnormal food habits. Eventually, anorexia nervosa can lead to numerous negative physical effects. The treatment of anorexia nervosa includes increasing food intake to support gradual weight gain. Psychological counseling attempts to help patients establish regular food habits and to find means of coping with the life stresses that led to the disorder. Bulimia nervosa is characterized by secretive bingeing on large amounts of food within a short time span and then purging by vomiting or misusing laxatives, diuretics, or enemas. Alternately, fasting and excessive exercise may be used to offset calorie intake. Both men and women are at risk. Vomiting as a means of purging is especially destructive to the body. The treatment of bulimia nervosa includes psychological as well as nutritional counseling. During treatment, bulimic persons learn to accept themselves and to cope with problems in ways that do not involve food. Binge- eating disorder is most common among people with a history of frequent, unsuccessful dieting. Binge eaters binge without purging. Thus, this condition falls under the category Eating Disorders Not Otherwise Specified (EDNOS). Emotional disturbances are often at the root of this disordered form of eating. Treatment addresses deeper emotional issues, discourages food deprivation and restrictive diets, and helps restore normal eating behaviors. The treatment of eating disorders may include certain medications.
11.0
- 1 The benefits of regular physical activity include enhanced heart function, improved balance, reduced risk of falling, better sleep habits, healthier body composition, and reduced injury to muscles, tendons, and joints. A gradual increase in regular physical activity is recommended for all healthy persons. A minimum plan includes 30 minutes of physical activity on most (or all) days; 60 to 90 minutes per day provides even more benefit, especially if weight control is an issue.
- 2 A good fitness program is one that meets a person’s needs. To reach goals, fitness program planning should consider the mode, duration, frequency, intensity, and progression of exercise, as well as consistency and variety. Before starting a new fitness program, discuss program goals with a health-care provider. Also, assess and record baseline fitness scores. Most new exercise programs should start with short intervals of exercise at the lower end of the maximum heart rate target zone and work up to a total of 30 minutes of activity incorporated into each day. To prepare and recover safely from an exercise session, a warm-up and cooldown period should be included.
11.3 At rest, muscle cells mainly use fat for fuel. For
intense exercise of short duration, muscles mostly use phosphocreatine (PCr) for energy. During more sustained intense activity, muscle glycogen breaks down to lactic acid, providing a small amount of ATP. For endurance exercise, both fat and carbohydrate are used as fuels; carbohydrate
is used increasingly as activity intensifies. Little protein is used to fuel muscles. Fuel sources for muscle cells can be estimated based on percent of VO2max.
11.4 Physical activity has many effects on the body. The most pronounced effects are typically seen in the muscular, circulatory, and skeletal systems. The body contains 3 major types of muscle tissue: skeletal muscle, smooth muscle, and cardiac muscle. Skeletal muscle is composed of 3 main types of muscle fibers, which have distinct characteristics. Prolonged, low-intensity exercise, such
as a slow jog, mainly uses type I muscle fibers, so the predominant fuel is fat. As exercise intensity increases, type IIA and type IIX fibers are gradually recruited; in turn, the contribution of glucose as a fuel increases. Type IIA and type IIX fibers also are important for rapid movements, such as a jump shot in basketball. The relative proportions of the 3 fiber types throughout the muscles of the body vary from person to person and are constant throughout each person’s life. With training, muscle strength becomes matched to the muscles’ work demands. Muscles enlarge after being made to work repeatedly. Repeated aerobic exercise strengthens the heart and increases in the number of capillaries in muscle tissue; as a result, oxygen can be delivered more easily to muscle cells. Another adaptation that occurs with exercise is increased bone density.
11.5 Athletic training and genetic makeup are very important determinants of athletic performance. Monitoring body weight is an easy way to
assess the adequacy of calorie
intake. Athletes should strive to
maintain weight during competition
and training. Athletes should obtain
at least 60% of total energy needs from
carbohydrates. Carbohydrate-loading
regimens usually increase muscle glycogen
stores 50 to 85% over typical conditions.
Carbohydrate loading is for athletes who
compete in continuous, intense aerobic events
lasting more than 60 to 90 minutes. A fat intake of
15 to 25% of energy is generally recommended for athletes. Typical recommendations for protein intake for most athletes range from 1.0 to 1.7 g of protein/kg of body weight. The extra protein is needed for the repair of tissue and the synthesis of new muscle that results from training. Vitamin and mineral needs are the same or slightly higher for athletes, compared with those of sedentary adults. The female athlete triad consists of 3 conditions: menstrual disorders, low energy availability, and low bone mineral density.
11.6 To maintain the body’s ability to regulate internal temperature, athletes must consume sufficient fluids because dehydration leads to a decline in endurance, strength, and overall performance and sets the stage
for heat exhaustion, heat cramps, and potentially fatal heatstroke. During exercise, the recommended fluid
status goal is a loss of no more than 2% of body weight.
To prevent hyponatremia, athletes should drink beverages containing sodium and should consume enough fluid during exercise to minimize the loss of body weight. Most experts recommend drinking sports drinks instead of water.
11.7 The composition of food eaten before, during, and after athletic events or exercise training sessions can affect performance and the speed with which the athlete recovers from the exercise bout. Pre-exercise training meals keep the athlete from feeling hungry before and during the exercise bout and maintain optimal levels of blood glucose for the exercising muscles. The pre-exercise meal should be high
in carbohydrate, non-greasy, and readily digested. For sporting events lasting more than 60 minutes, consuming carbohydrate during activity can improve athletic performance. Carbohydrate-rich foods should be consumed 30 minutes after exercise and again 2 hours after exercise.
11.8 An ergogenic aid is a nutritional, psychological, pharmacological, mechanical, or physiological substance or treatment intended to improve exercise performance. Most of these aids are ineffective.
12.0
12.1 Vitamins are essential, organic compounds needed for important metabolic reactions in the body. They are not
a source of energy. Instead, they promote many energy- yielding and other reactions in the body, thereby aiding in the growth, development, and maintenance of various body tissues. Vitamins cannot be synthesized in the body at all or are synthesized in insufficient amounts. Vitamins A, D, E, and K are fat soluble, whereas the B-vitamins and vitamin C are water soluble. Fat-soluble vitamins are absorbed along with dietary fat. They travel by way of
the lymphatic system into general circulation, carried by chylomicrons. In disease states that limit fat digestion, fat- soluble vitamin absorption may be compromised, thereby increasing the risk of deficiency in these individuals. Fat- soluble vitamins are excreted less readily from the body than water-soluble vitamins and thus pose a potential threat for toxicity, especially of vitamins A and D. Toxicities of these fat-soluble vitamins generally
occur with high doses of supplements, rather than
from foods.
12.2 Vitamin A consists of a family of retinoid compounds: retinal, retinol, and retinoic acid. A plant derivative, known as beta-carotene,alongwith2other carotenoids, yields vitamin A after metabolism by the small intestine or liver. Vitamin A is found in foods of animal origin, such as liver, fish oils,
and fortified milk. Carotenoids are
obtained from plants and are especially
plentiful in dark green and yellow-orange vegetables and fruits. Vitamin A contributes to the maintenance of vision, the normal development of cells (especially mucous-forming cells), and immune function. Preformed vitamin A can be quite toxic when taken at doses 2 to 4 times or more the RDA. Use of vitamin A supplements is especially dangerous during pregnancy because it can lead to fetal malformations.
12.3 VitaminDcanbeobtainedfromfoodanditisproduced by the body. The synthesis of vitamin D3 begins with a precursor of cholesterol synthesis located in the skin and depends on ultraviolet light. With adequate sun exposure, no dietary intake of vitamin D is needed. Vitamin D food sources include fish oils and fortified milk. The provitamin, whether produced in the skin or obtained from the diet,
is metabolized in the liver and kidneys to yield 1,25(OH)2 vitamin D3 (or calcitriol), the active form of vitamin D.
Calcitriol is important for calcium and phosphorus absorption from the intestine and, along with other hormones, for the regulation of bone metabolism. It also is important in gene expression and immune function. Risk
of vitamin D deficiency may be greater than previously observed, especially in the elderly and individuals lacking regular sunlight exposure. Vitamin D deficiency results in harmful changes in bone, a condition known as rickets in children and osteomalacia in adults. Toxicity of vitamin D can occur with excess supplementation of vitamin D, causing the deposition of calcium in the kidneys, heart, and lungs.
12.4 Vitamin E functions as an antioxidant. By donating electrons to electron-seeking or oxidizing compounds (e.g., free radicals), it neutralizes their action and prevents the widespread destruction of both cell membranes and DNA. Vitamin E is 1 of several components
in the body’s defense system against oxidizing agents. Vitamin E is plentiful in plant oils
and food products that contain these oils. Overt vitamin E deficiency is rare. Toxicity from megadose therapy inhibits vitamin K
activity and, in turn, increases the risk of hemorrhage.
12.5 VitaminKcontributestothe body’s blood-clotting ability by
facilitating the conversion of precursor proteins, such as prothrombin, to
active clotting factors that promote blood coagulation. Vitamin K also plays
a role in bone metabolism. About 10% of the vitamin K absorbed each day comes from bacterial
synthesis in the intestine. Most vitamin K comes primarily from green leafy vegetables and vegetable oils in the diet. Vitamin K deficiency is rare, but it can occur in newborns. Thus, newborn infants are given vitamin K injections shortly after birth as a preventive measure.
12.6 Taking a multivitamin and mineral supplement to helpmeetnutrientneedsisrecommendedbysome experts, but others suggest that only some people
need them. Taking many nutrient supplements can
lead to nutrient-related toxicity, so their use should be considered carefully. The clearest evidence for good nutrition supports a diet rich in fruits and vegetables and whole-grain breads and cereals, rather than relying on supplements to meet nutritional needs.
13.0
- 1 The water-soluble vitamins are the 8 B-vitamins and vitamin C. A dietary source of choline also is required. The B-vitamins function as coenzymes. Deficiency symptoms typically show up in the skin, GI tract, brain, and nervous system. The water-soluble vitamins are generally stored in the body to a lesser extent than the fat-soluble vitamins. Compared with fat-soluble vitamins, water-soluble vitamins are more easily destroyed during cooking. Cereals and grains are enriched with thiamin, riboflavin, niacin, and folic acid.
- 2 Thiamin in its functional form as TPP serves as a coenzyme in energy release. Thiamin deficiency results in the disease beriberi. In North America, alcoholics are at risk of thiamin deficiency. Pork, pork products, and enriched grains are reliable sources of thiamin.
- 3 Riboflavin coenzymes, FAD and FMN, participate in a wide variety of oxidation-reduction reactions, including those in numerous metabolic pathways that produce energy. A specific riboflavin deficiency is unlikely but could accompany other B-vitamin deficiencies. Dairy products and enriched grains are good dietary sources.
- 4 Niacin as NAD+ and NADP+ are coenzymes. NAD+ is important in oxidation-reduction reactions in energy-yielding pathways. A deficiency of the vitamin produces the disease pellagra, which is seen most often in corn-based diets. Alcoholism can lead to a deficiency. Food sources of niacin are enriched cereal grains and protein foods. The body is able to synthesize the vitamin from the amino acid tryptophan. Megadoses of niacin produce a variety of toxic symptoms.
- 5 Among its functions, pantothenic acid in coenzyme form (CoA) shuttles 2 carbon fragments from the metabolism of glucose, amino acids, fatty acids, and alcohol into the citric acid cycle during energy metabolism. A deficiency of pantothenic acid is unlikely because it is widely distributed in foods.
- 6 Biotin functions as a cofactor in enzymes that add carbon dioxide to a substance. Biotin is widely distributed in foods. Intestinal bacteria also synthesize biotin. No deficiency exists in healthy people.
- 7 The vitamin B-6 coenzyme PLP participates in amino acid metabolism, especially the synthesis of non-essential amino-acids. It is essential in the synthesis of heme in hemoglobin, the formation of certain neurotransmitters, and the metabolism of homocysteine. Anemia, convulsions, and decreased immune response are symptoms of a deficiency. Animal protein foods, a few fruits and vegetables, and whole-grain cereals are good sources of this vitamin. Toxic effects from excess consumption include nerve damage.
- 8 Folate in its many coenzyme forms (tetrahydrofolic acid) accepts and donates 1-carbon groups. The most notable function performed by folate is in DNA synthesis. It also participates in homocysteine metabolism. A dietary lack of this vitamin produces megaloblastic anemia and increases the risk of spina bifida. Deficiency is common among alcoholics. Folate is found in green vegetables, legumes, liver, and fortified cereal grains.
13.9 Vitamin B-12 in its coenzyme form transfers 1-carbon groups. Because of its interaction with folate, a deficiency of vitamin B-12 results in the same type of megaloblastic anemia, as well as excess homocysteine in the blood. Defective absorption of vitamin B-12 is the cause of
the deficiency disease pernicious anemia. In such cases, injection of the vitamin or another pharmacological approach is necessary. Vitamin B-12 is found in animal foods, but not in plant foods. Vegans need to look for foods fortified with the vitamin or take it as part of a multivitamin and mineral supplement.
13.10 Choline is a dietary component that is available from
a wide variety of foods and is synthesized in the
body. Choline is required for the formation of the neurotransmitter acetylcholine and it is incorporated into phospholipids. No natural deficiency of choline has been reported.
13.11 Vitamin C functions as an electron donor in many processes, including the synthesis of collagen, a protein
in connective tissue. A deficiency of vitamin C causes the disease scurvy. Fresh fruits and vegetables are reliable sources of this vitamin. Like folate, vitamin C is destroyed by heat. Among North Americans, alcoholics, smokers, and individuals who do not eat many fruits or vegetables are most likely to develop a deficiency.
13.12 Carnitine and taurine, although participating in many important biochemical reactions in the body,
are not true vitamins because they
can be synthesized in the
body from readily available precursors. In some medical circumstances, dietary intake
may be needed
to augment cellular production.
14.0
14.1 Water accounts for 50 to 75% of the weight of the human body. The intracellular compartment holds two-thirds
of the body’s water, with the balance in the extracellular compartment. Electrolytes dissolved in the body’s water help maintain fluid balance. Water’s unique chemical properties enable it to dissolve substances and to serve as
a medium for chemical reactions, temperature regulation, and lubrication. For adults, daily fluid needs are estimated at 9 cups (women) to 13 cups (men), but temperature, physical exertion, and other factors can greatly affect water requirements. Water balance is regulated by hormones that act on the kidneys. A water deficit results in dehydration, but too much water can cause the rare condition of water intoxication and hyponatremia.
14.2 Minerals are divided into the major and trace minerals. Animal foods are the best sources of calcium, iron, and zinc. Plant foods are good sources of potassium and magnesium. The absorption of minerals can be affected by the need for the minerals, the consumption of supplements, and the presence of phytic and oxalic acids. Minerals
are needed for water balance, the transmission of nerve impulses, and muscle contraction. They function as enzyme cofactors and as components of body tissues. Minerals taken in excess can be toxic.
14.3 Sodium, the major positive ion (cation) found outside cells, is vital in fluid balance and nerve impulse transmission. The processed foods and table salt. Sodium intakes often
exceed the Upper Level. A high sodium intake is linked to hypertension.
14.4 Potassium, the major positive ion (cation) found inside cells, has functions similar to those of sodium. Milk, fruits, and vegetables are good sources. Potassium intakes in the U.S. fall below the Adequate Intake. Low potassium diets increase the risk of hypertension and stroke. Too much potassium is only a problem when kidney function is poor.
14.5 Chloride is the major negative ion (anion) found outside cells. It is important in digestion as part of gastric hydrochloric acid and in immune and nerve functions. Table salt supplies most of the chloride in our diets. Hypertension is a serious health problem that afflicts
1 in 3 adults. It increases the risk of cardiovascular disease, stroke, dementia, and kidney and eye disease. The cause of hypertension is not known, but contributors are an impaired ability of the kidney to excrete sodium along with increased arterial resistance. Hypertension
is higher in those who are older, African American, overweight, or have diabetes. The DASH diet, low in sodium and fat, and high in fiber, potassium, magnesium, and calcium is effective in treating hypertension. Weight
reduction, limiting alcohol,
and increasing physical activity also play a role. Hypertension often is treated with medication when lifestyle measures are not adequate.
14.6 Calcium forms a vital part of bone structure and is very important in blood clotting, muscle contraction, nerve transmission, and cell metabolism. Calcium absorption is enhanced by stomach acid and the active vitamin D hormone. Milk and milk products are rich calcium sources and calcium supplements can help meet calcium needs. In addition to its role in bone formation, calcium may help reduce the risk of colon cancer. Researchers are trying to understand if calcium and dairy intake are related to body weight regulation. Osteoporosis is a disease that develops over many years and is more common in women than in men. It represents an increase of bone resorption over bone building. The prevention and treatment of osteoporosis involve consuming adequate bone-building nutrients, engaging in weight-bearing physical activity, minimizing the risk of falls, not smoking, and limiting alcohol intake. Supplemental vitamin D and calcium may help prevent a decrease in bone mineral density and fractures. Medications to treat osteopenia and osteoporosis are available.
14.7 Phosphorus is a part of ATP and other key metabolic compounds, aids the function of some enzymes, and forms part of cell membranes and bone. It is efficiently absorbed, and deficiencies are rare. Typical food sources are dairy products, bakery products, and meats.
14.8 Magnesium, a mineral found mostly in plants, is important for nerve and heart function and as a cofactor for many enzymes. Whole grains (bran portion), vegetables,
nuts, seeds, milk, and meats are typical food sources. Magnesium deficiency causes irregular heartbeat, weakness, disorientation, nausea, vomiting, and seizures. This can be seen in those who abuse alcohol and take certain diuretics. The UL refers only to supplements. Intakes over the UL can cause diarrhea.
14.9 Sulfur is incorporated into certain vitamins and amino acids. Its ability to bond with other sulfur atoms enables it to stabilize protein structure. There is no AI, RDA, or UL established for sulfur.
15.0
15.1 The absorption of iron depends on the body’s need for iron and on the form of iron in food (heme vs. non-heme). Heme iron (from animal-based foods) is better absorbed than non-heme iron (primarily from plant-based foods). Liver, beef, and seafood are the best sources of dietary iron. The iron in plant foods is poorly absorbed. The
body cannot readily excrete excess iron. Thus, the body regulates iron absorption and iron storage to maintain iron homeostasis. Iron is a critical component of hemoglobin, myoglobin, and many enzyme systems. Two-thirds of the body’s iron is contained in hemoglobin, where it helps transport oxygen from the lungs to the tissues. In the
early stages, iron deficiency does not result in obvious physical symptoms because iron stores can be mobilized to temporarily maintain many of iron’s functions. As stores are depleted, iron deficiency anemia develops, causing fatigue, weakness, increased infection rate, delayed growth, and impaired brain development. Accidental iron overdose is the leading cause of poisoning in toddlers and young children. In adults, iron toxicity usually occurs from
excess supplementation or from a genetic disorder, called hemochromatosis, that causes an overabsorption of iron.
15.2 Like iron, zinc absorption is affected by the need for the mineral and the amount in the diet. Absorption also plays a primary role in maintaining zinc balance. The best sources of zinc are oysters, meat, nuts, legumes, and whole grains. Zinc functions as a component of proteins and enzymes involved in stabilizing the structures of cell membrane proteins, reproduction, growth and development, immune function, and antioxidant defense (with copper as Cu/Zn SOD enzymes). Zinc deficiency causes impairments in taste, appetite, immune function, growth, sexual development, and reproduction. In many parts of the world, zinc deficiency (like iron deficiency) is still a serious public health concern. Zinc toxicity also is of concern in populations where zinc supplementation has become more common.
15.3 The best dietary sources of copper are liver, legumes, whole grains, and dark chocolate. Copper is involved in the mobilization of iron from body stores, in the cross-linking of proteins in connective tissue formation, and as a part
of antioxidant defense. Although copper deficiency and toxicity are rare in humans, RDA and UL guidelines have been established to promote intakes within safe ranges.
15.4 Manganese is found in whole grains, nuts, legumes, and tea. Manganese functions in antioxidant defense and as a component of different metabolic enzymes. Manganese deficiency and toxicity rarely have been reported in humans.
15.5 Iodine is an essential part of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) and thus plays a role in many metabolic and developmental functions in the body. The iodine content of the soil in which a plant was grown determines the iodine content of the plant food. The iodine content of most foods is low; thus, many populations obtain iodine from iodized salt. Iodination has eradicated endemic iodine deficiency in these areas. In countries where the iodination of salt, oil, or other food products is not available, iodine deficiency is a serious health concern. Iodine deficiency results in enlargement of the thyroid gland (goiter) and severe growth and mental impairment (cretinism).
15.6 Selenium acts as a cofactor for glutathione peroxidase, which prevents the oxidative destruction of cell membranes by hydrogen peroxide and free radicals. Selenium also aids in the conversion of the thyroid hormone T4 to T3. The selenium content of the soil in an area greatly affects the amount of selenium in the foods from that area. In general, meat, eggs, seafood, grains, and seeds are the best sources of selenium. In areas where the soil lacks selenium, deficiencies are more prevalent. Selenium deficiency increases the risk of Keshan disease and possibly of certain cancers. Because selenium has a narrower range of safety for intake than most other trace minerals, selenium supplementation can cause symptoms of toxicity at lower levels of intake.
- 7 The functions of chromium are not fully known. Chromium may enhance the action of insulin and promote the uptake of glucose into cells. Chromium is widely distributed in a variety of foods. Chromium deficiency and toxicity have not been well documented in humans.
- 8 Although fluoride is not truly classified as an essential trace mineral, it is beneficial in decreasing the incidence of dental caries. Most North Americans obtain fluoride from fluoridated drinking water, toothpaste, mouth rinses, and dental treatments. Excess fluoride causes discoloration of the teeth, known as enamel mottling or fluorosis.
15.9 The best dietary sources of molybdenum are legumes, grains, and nuts. Molybdenum is a component of several enzymes involved in nitrogen metabolism. Reports of molybdenum deficiency and toxicity are very rare. Boron, nickel, silicon, vanadium, and arsenic are classified as ultratrace minerals. Further research is needed to determine their functions in the body. Cancer is a disease that develops from uncontrolled replication of mutated cells. It begins by exposure to cancer- causing agents (carcinogens) such as tobacco, radiation, viruses, and certain dietary factors. Low intakes of fruits
and vegetables, antioxidants, calcium, and vitamin D and excessive intakes of energy, red meats, fried foods, alcohol, and dietary fat have been associated with increased risk of cancer.
16.0
6.1 A favorable pregnancy outcome is one lasting the full- term gestation period that results in a live, healthy infant weighing more than 5.5 pounds and permits the mother to return to her prepregnancy health status. Low birth weight babies weigh less than 5.5 pounds and have a high infant mortality rate. Low birth weight often is associated with premature birth. Full-term and preterm infants who weigh less than the expected weight for their duration
of gestation are described as small for gestational age. A critical period is the specific time during embryonic or fetal life when cells develop into a particular tissue or organ. Nutrient deficiencies or excesses can interfere with normal development and cause physical or mental abnormalities. The zygote nourishes itself by absorbing secretions from glands in the uterus and digesting some of the uterine lining. Then, the placenta takes over the role of delivering nourishment to the developing offspring. The placenta contains both maternal and fetal blood vessels, which are so close together that nutrients and oxygen pass easily from the mother to the fetus and fetal wastes are shuttled from the fetus to the mother for excretion.
16.2 A pregnant woman needs additional calories and more of almost every nutrient than a non-pregnant woman to support the growth and development of the fetus, placenta, and mother’s body. Pica, the eating of non- food substances, can have dire consequences for the pregnant woman and her fetus.
16.3 A pregnant woman’s meal plan should include nutrient- dense foods from every food group. Special vitamin
and mineral supplements formulated for pregnancy
are prescribed routinely for pregnant women by most
physicians. A low- or moderate-intensity exercise program
offers physical and psychological benefits to a woman experiencing
a normal, healthy pregnancy.
16.4 An infant’s birth weight is closely related to
length of gestation, the
mother’s prepregnancy
weight, and the
amount of weight she
gains during pregnancy. The physical and hormonal changes that affect almost every aspect of the woman’s body begin soon after the egg is fertilized and may cause nutrition-related problems, such as heartburn, constipation, morning sickness, and edema.
16.5 Lactation (breastfeeding) is a natural physiological process that occurs in the postpartum period, when the mother’s breast secretes milk and suckles the offspring. Prolactin is the principal hormone that promotes milk production. The let- down reflex occurs when oxytocin causes milk to be released from the milk-producing lobules. The let-down reflex is easily inhibited by nervous tension, a lack of confidence, and fatigue. Colostrum is a thin, yellowish, “immature” milk that appears anytime from late pregnancy to several days postpartum. Mature human milk is thin and almost watery in appearance; with the possible exceptions of vitamin D and iron, it supplies all the nutrients the growing baby needs.

16.6 A lactating woman’s DRI is based on the quantity of milk should come from her diet, with the remainder supplied by produced by the average mother, its nutrient content, and the fat stored during pregnancy. Breastfeeding offers benefits the amounts of her nutrient stores used to produce milk. to the infant and mother.
If the mother’s diet is poor for a prolonged period and she
has depleted nutrient stores, the quantity of milk produced may decline. Maternal malnutrition must be extremely severe before the quality of milk produced drops. The average breastfeeding woman uses about 800 calories per day during the first 6 months of lactation to produce
750 ml of milk daily. Approximately 400 to 500 calories
16.7 Maternal factors that can negatively affect breastfeeding success include high prepregnancy weight, young age, long-term poor nutrient intake, certain diseases, lack of information and role models, and an inadequate support system. Compounds in the food that the mother eats, including contaminants, caffeine, alcohol, drugs, and nicotine, can be secreted into her milk.
17.0
�17.1 Normal growth and development are highly dependent on calorie and nutrient intake. Physical growth rate is at its peak velocity during infancy, slows during childhood, then increases again during adolescence. During the growing years, height and weight increase, body composition changes, and body organs and systems mature.
17.2 The single best indicator of a child’s nutritional status
is growth. Growth charts matched to a child’s gender
are used to track physical growth over time to identify a child’s growth percentile curves and determine if growth is progressing normally. BMI-for-age (or weight-for-length for children younger than 2 years old) is a good indicator of recent nutritional status. Stature-for-age is a good indicator of long-term nutritional status. Infants and young children who do not grow at the expected rate for several months and are dramatically smaller or shorter than other children the same age, especially those who fall below the 5th percentile, experience failure to thrive. Continually receiving minimal quantities of food may permanently
and irreversibly stunt growth and development. Growth in height ceases when the growth plates at the ends of the bones fuse.
17.3 The greatest calorie and nutrient needs, pound for pound, occur during infancy. The total quantity of calories and nutrients needed rises throughout childhood. The total quantities of nutrients and calories needed are greater during adolescence than at any other time, except pregnancy and lactation. Adolescent males need more of many nutrients than females because males are larger, develop more muscle mass and bone density, and have a longer, more intense growth period. Total fat should account for about 40 to 55% of a baby’s calorie intake. It is wise to reduce fat intake gradually between ages 2 and 5 years until children are getting an average of 30 to 35% of their calories from fat. Dietary recommendations meant to reduce the risk of heart disease do not apply to children younger than 2 years old. Water is of special importance for babies because they have a large body surface area per pound of weight, turn over body water quickly, produce a large quantity of wastes, and have inefficient kidneys. A young baby’s need for water is usually met by human milk or formula. However, giving infants too much water can lead to water intoxication. Newborns frequently have low stores of fluoride, vitamin K, and vitamin D. Many children and adolescents consume too little calcium, zinc, folate, and vitamins A and C. With few exceptions, human milk or iron-fortified infant formula and the baby’s internal nutrient stores meet an infant’s nutrient needs at least until age 4 to 6 months. Human milk is the most ideal and desirable source of nutrients for infants. Commercial iron-fortified infant formulas provide a safe, nutritious alternative to human milk. Breastfed infants must be followed closely over the first week of life to ensure that feeding and weight gain are proceeding normally. All equipment and utensils used to prepare, store, and/or feed infant formula or human milk should be thoroughly washed and rinsed.
17.5 When to introduce solid foods into an infant’s diet hinges on the infant’s nutritional needs, physiological capabilities, and physical ability. Between 6 and 12 months of age, human milk or formula intake gradually decreases while solid food intake slowly increases. The recommended sequence for introducing solid foods is iron-fortified baby cereal, juices and pureed fruits and vegetables, protein-rich foods, finger foods, and table foods. Parents should wait until the child is a year old before serving egg whites and unaltered cow milk because they frequently cause allergic reactions in younger babies. Infants should never be put to bed with a bottle or placed in an infant seat with a bottle propped up.
17.6 Compared with babies, children tend to have erratic appetites. Pressuring a child to eat more or less than desired tells the child not to trust his or her own hunger and satiety signals—this can lead to a lifetime battle with weight problems. Offering children 6 or so small meals succeeds better than limiting them to 3 meals daily. A serving size for children is equal to about 1 tablespoon per year of
age, depending on the child’s appetite. MyPyramid for children is a useful meal planning tool. The most important nutrition lessons for children of all ages involve expanding their familiarity with new foods and helping them develop
a willingness to accept new foods. Many preschool children go through periods of unpredictable and unusual eating behavior, such as going on food jags, refusing to eat, and being a picky eater. The best way to handle most of these behaviors is to not overreact, offer a variety of healthy foods, and let the child exert some autonomy over the specific types of food and amounts eaten.
17.7 The types and amounts of foods recommended for teenagers are the same as those for adults, except that teens have a greater need for calcium. The diets of teens are less than optimal because teens frequently eat out, skip meals, and snack. The struggle to establish independence and individual identity, gain peer acceptance, and cope with their heightened concern about physical appearance affects teens’ food choices. Other factors that affect their food choices are perceived and desired body image, participation in athletics, and substance use. MyPyramid is a useful tool for teenage meal plans. Common nutrition-related health problems during the growing years are iron deficiency anemia,
colic, gastroesophageal reflux, milk allergy, constipation, diarrhea, ear infections, dental caries, and obesity. Parents usually need to consult a physician when dealing with many nutrition-related conditions. Children from families with histories of early development of cardiovascular disease or high blood cholesterol should be screened for high blood cholesterol levels and, if necessary, treated with appropriate dietary changes and possibly medication.
18.0
18.1 During adulthood, nutrients are used primarily to maintain the body rather than support physical growth.
As adults get older, nutrient needs change. Adulthood is characterized by body maintenance and gradual physical and physiological transitions, often referred to as “aging.” The physiological changes of aging are the sum of cellular changes, lifestyle practices, and environmental influences. Many of these changes can be minimized, prevented, and/or reversed by healthy lifestyles. Usual aging refers
to the age-related physical and physiological changes that are commonly thought to be a typical or expected part of aging. Successful aging describes the declines in physical and physiological function that occur because one grows older. Striving to have the greatest number of healthy years and the fewest years of illness is referred to as compression of morbidity. The rate at which one ages is individual; it is determined by heredity, lifestyle, and environment.
18.2 A healthy diet based on the 2005 Dietary Guidelines for Americans can help people preserve the body’s function, avoid chronic disease, and age successfully. American adults are fairly well nourished, although common dietary excesses are calories, fat, sodium, and, for some, alcohol. Common dietary inadequacies include vitamins D and E, folate, magnesium, calcium, zinc, and fiber. People ages
65 and up, particularly those in long-term care facilities
and hospitals, are the single largest group at risk of malnutrition. The Nutrition Screening Initiative checklist can help identify older adults at risk of nutrient deficiencies. The DRIs for adults are divided by gender and age to reflect how nutrient needs change as adults grow older. These changes in nutrient needs take into consideration aging-related physiological alterations in body composition, metabolism, and organ function.
18.3 The food choices and nutritional adequacy of adults’
diets depend on physical, physiological, psychosocial, and economic factors. Alterations in any 1 of these factors
can result in deteriorations in the quality of dietary
intake, nutritional status, and health. The physical and physiological changes in body composition and body systems that occur during adulthood can influence
dietary intake, alter nutrient and/or calorie needs,
and/or alter nutrient utilization. The use of medications and supplements can improve health and quality of life, but some also can adversely affect nutritional status. Psychosocial status can affect food intake and health. Economic factors can have a great impact on the types and amounts of food one eats.

18.4 Programs publicly funded by the U.S. Department of Agriculture (USDA) and U.S. Administration on Aging provide food and nutrition services for adults. The USDA administers food and nutrition assistance programs, including the Commodity Foods Program, Food Stamp Program, Child and Adult Care Food Program, and Senior Farmers’ Market Nutrition Program. The U.S. Administration on Aging administers the Older Americans Act, which provides community-based nutrition, health, and supportive services and may include adult day care, senior center activities, transportation, information and counseling services, and health and physical activity programs. The Congregate Meal Program and Home Delivered Meal Program can help older people obtain some of the food needed for good health.
18.5 Diet is a primary factor directly involved in the development of several health conditions during adulthood, including atherosclerosis, cancer, constipation, diabetes, diverticular disease, heartburn, hypertension, obesity,
osteoporosis, and periodontal disease. The consequences
of alcohol use, especially alcohol abuse, rise with advancing age. A slowdown in the restoration of the internal balance of the body (homeostasis) is at least partially diet-related. Arthritis and Alzheimer’s disease are considered by some
to be diet-related, even though scientific evidence currently indicates otherwise. Complementary and alternative medicine (CAM) is any medical or health-care system, practice, or product not presently part of conventional medicine. The CAM categories are biological treatments, mind-body interventions, energy medicine, manipulative and body-based practices, and alternative systems of medical practices. Most alternative therapies have little
or no scientific evidence to support them. Some herbal products may be harmless, others are potentially toxic,
and still others may be effective for some problems but dangerous when taken in the wrong dose or by people with certain medical conditions. Herbal products should be used with great caution.
