Lecture 4 Carbohydrates Flashcards
(16 cards)
What are the two main groups of carbohydrates?
1) Simple Carbohydrates o Monosaccharides (Glucose, fructose, Galactose) o Disaccharides (Maltose, Sucrose, Lactose)
2) Complex Carbohydrates o Oligosaccharides o Polysaccharides • Glycogen • starches • Fibers
What are the three types of Monosaccharides?
A) Monosaccharides: Single Sugars:
1) Glucose
• Glucose is the basic sub-unit of other larger carbohydrate molecules
• This is the form of carbohydrate, used by the body, commonly referred to as “blood sugar”
- It can be found in fruits, vegetables, honey etc.
- All forms of single sugars are converted to glucose by the liver
2) Fructose
• Is the sweetest of all the single sugars
• It occurs naturally in various fruits & honey commonly referred to as “fruit sugar”
• High fructose corn syrup is sweeter and less expensive than sugar, so it is used to sweeten many products
3) Galactose
• Combines with glucose to make lactose
What are Disaccharides?
Disaccharides: Pairs of Monosaccharides
• The linking of 2 monosaccharides produces a disaccharide
• Two different bonds exist: alpha and beta bonds
• Beta bonds cannot easily be broken down by digestive enzymes , therefore foods containing these types of bonds are often difficult (or impossible to digest) ex. lactose
What are the 3 different types of disaccharides?
1) Sucrose (“table sugar”)
•Is a combination of glucose + fructose (alpha bond)
•Found in many fruits, grains, vegetables
•It is made from sugar cane and sugar beets
2) Lactose (“milk sugar”)
• A combination of glucose + galactose (beta bond)
• It is found in milk and dairy products
• The beta bond makes this hard to digest for many people causing (intestinal gas, cramping, bloating etc.)
3) Maltose (“malt sugar”)
• Is a combination of glucose + glucose (alpha bond)
• It is a product of starch breakdown & fermentation of cereal grains (to make alcoholic beverages)
• Few other foods or beverages contain maltose
What are the 2 main “Complex Carbohydrates”?
A) Oligosaccharides:
• These are short carbohydrate chains of 3-10 monosaccharides
• They are found in dried beans, peas, lentils and human milk
• Examples: Raffinose, and Stachyose (in onions, cabbage, broccoli and legumes) cannot be broken down by human enzymes, though can be digested by colonic bacteria producing gas.
B) Polysaccharides: (AKA Complex Carbohydrates)
• Long carbohydrate chains of monosaccharides (100’s-1000’s of glucose molecules) linked by alpha or beta bonds
• Some are digestible, others not.
• Digestibility depends on whether the glucose units are linked by alpha or beta bonds.
• Alpha (a) bonds easily broken by human enzymes
• Beta (b) bonds indigestible by human enzymes
What are the 2 digestible polysaccharides?
Digestible Polysaccharides:
1) Starch:
• The major digestible polysaccharide in our diet
• Two types of plant starch exist: amylose & amylopectin
• Amylose– long un-branched chains of glucose molecules
• Amylopectin – long branched chains of glucose molecules
• Enzymes only act on the ends of the molecules, therefore Amylopectin is digested more readily, which elevates blood glucose more quickly.
• These are important dietary sources of carbohydrates, abundant in potatoes, beans, breads pasta, & rice
2) Glycogen
• These are highly branched chains of glucose units
• This is the animal storage form of carbohydrate
• It is found only in liver and muscle and is an important supply of glucose during high intensity exercise.
• Though the human diet includes a lot of meat, it is not a significant dietary source of carbohydrate. After slaughter, tissue enzymes break down most glycogen within 24 hours.
Fiber is an _________ polysaccharide. Describe soluble and insoluble fibers.
1) Fiber is an “indigestible” fiber.
• These are non-digestible polysaccharides that are found in plants
• They have monosaccharides linked by Beta bonds, (which are not broken down by human digestive enzymes) so they pass through the small intestine into the large intestine where some can be metabolized by bacteria.
• Fiber has health benefits when consumed in adequate quantities
• Fibers can be classified based on solubility in water (soluble vs. insoluble)
• Insoluble fiber:
o Found in the structural part of the cell wall in vegetables and grains (so are found in the outer layers of grains and fruits and vegetables
o Are more resistant to being broken down by bacteria, and they do not dissolve in water
o Examples: cellulose, hemicellulose, lignin
o Food sources: whole grains, outer skin of vegetables and fruits
• Soluble fiber:
o These fibers dissolve easily in water, and become gel like in consistency.
o Examples: gum, pectin, mucilage
o More readily digested by intestinal bacteria
o They are found in oat bran, fruit, legumes and psyllium
What is the recommended intake of carbohydrates?
To provide for total body energy needs it is recommended to consume 45-65% of total energy intake as carbs.
- Most of the carbohydrates should come from fiber rich fruits and vegetables and whole grains with little added sugar and sweeteners.
- Leading carbohydrate sources for US adults are white bread, soft drinks, cakes, donuts, sugars, syrups, jams and potatoes.
What are some faults with our carbohydrate intake?
• We consume about the correct % of carbs in the diet (50%), the types of carbs is incorrect:
- Too much added sugar to our diet (often due to consumption of sweetened drinks)
- Not enough fiber (due to low intakes of fruits and veggies)
- Too much intake of refined carbs– pasta, corn chips, white rice, white bread, cookies, candies, pop, etc.
Digestible carbohydrates: What is energy, sparing body protein, and ketosis?
1) Energy:
• Carbs are the most efficient energy form
• Glucose fuels most of body’s cells
• It is the preferred fuel for Nervous tissue (the brain, nerves) and
Red blood cells (RBC’s)
2) Sparing Body Protein:
- Inadequate carbohydrate consumption in the diet causes the body to break down amino acids and other tissues to make glucose (gluconeogenesis)
- RBC’s and nervous tissue require a continuous supply of glucose, so when carbohydrate consumption is less than < 50 - 100 g, body protein will be used to make glucose
- if carbohydrate is consumed adequately in diet, then body proteins will be spared
3) Preventing Ketosis (Anti-ketogenic)
- Some carbohydrate intake (50-100 g/day) is necessary for the complete breakdown of fat to CO2 and H20.
- When the intake of carbohydrates is inadequate, there is incomplete breakdown of fats which results in production of ketones
- An accumulation of ketones is referred to as Ketosis (or since ketones are acidic, this disrupts acid-base balance in the body leading to Ketoacidosis)
- Many low carb weight reduction diets (Atkins, South Beach Diet) use low carb intakes to promote ketosis which suppresses appetite and increases water loss from the body. Over time this can lead to loss of lean body mass, electrolyte imbalances, and even coma and death.
What are the benefits of indigestible carbohydrates>
Indigestible Carbohydrates:
A) Promotes bowel health
• Insoluble fibers aid in enlarging stool size, which stimulates intestinal muscles to ease passage of stools to aid elimination.
• This promotes regularity and reduces the force necessary to expel the feces, which decreases the risk of diverticulosis which when inflamed become diverticulitis) and maybe hemorrhoids.
• The faster transit time (or the higher nutrient intake of high fiber foods) may also lower incidence of colon cancer
B) Promotes weight control
• A diet high in Soluble fiber contributes to satiety (fills you up) without contributing many calories, and slows gastric emptying, delaying hunger.
C) Enhances Blood Glucose Control:
• Soluble fibers slow glucose absorption from the small intestine, contributing to better blood glucose regulation. (can be helpful for the treatment and maybe, prevention of, type 2 diabetes.
D) Reduces Cholesterol Absorption
• Soluble fibers help reduce blood cholesterol levels by inhibiting absorption of cholesterol and bile acids which reduces the risk of cardiovascular diseases and gallstones.
What is the goal of carbohydrate digestion? What are the 4 steps in this process of digestion?
Carbohydrate Digestion
• The goal of carbohydrate digestion is to break down the big complex molecules into monosaccharide units that are small enough to be absorbed.
1) Mouth:
• Chewing initiates mechanical digestion
• Salivary amylase begins digestion of starch (chemical digestion)
2) Stomach:
• Low pH inactivates salivary amylase, carbohydrate digestion halts
• Fibers remain in the stomach longer, delaying gastric emptying
3) Small Intestine
• The Pancreas secretes pancreatic amylase (pancreatic juice) which breaks downs starch into shorter glucose chains
• Enzymes located on the cell membranes of the intestinal epithelial cells complete digestion
• Maltase digests maltose producing: glucose + glucose
• Sucrase digests sucrose producing: glucose + fructose
• Lactase digests lactose producing: glucose + galactose
4) Large Intestine:
• Indigestible carbohydrates (fiber) cannot be broken down by enzymes, so they pass to the large intestine where they can be broken down by bacteria or excreted as fecal waste.
How are carbohydrates absorbed?
Of all forms of carbohydrates only the monosaccharides can be absorbed.
- Glucose & galactose are absorbed by active transport (requires a carrier and energy)
- Fructose is absorbed by facilitated diffusion (requires a carrier and no energy)
- Since facilitated diffusion occurs more slowly, fructose produces a smaller rise in blood sugar compared to glucose and galactose.
- Once absorbed all three types of monosaccharides travel in the portal vein to the liver where they are converted to glucose
- Some of the glucose is used for the various functions performed by the body’s cells. The remaining glucose molecules are synthesized into glycogen and are stored in the liver and muscle.
- Once energy requirements are met and glycogen storage sites are full, excess glucose is then converted to fat and stored in the adipose tissue.
What is a “High Sugar Diet” and what are the risks?
1) High Sugar Diets:
• Americans eat 20 tsps (82g.) of sugar/day!
• Most comes from foods/beverages where sugar has been added during processing and/or manufacturing
• Major sources of foods with added sugars are: soft drinks, cakes, cookies, ice cream (even low fat and fat free products)
• Sugar is also present in the following: barley malt, brown rice syrup, corn syrup, dextrose, evaporated cane-juice invert syrup, fructose, fruit juice, galactose, glucose, high fructose corn syrup, honey, lactose, maltodextrin, maple syrup, molasses, organic cane juice, sorghum, sucrose, turbinado.
• Risks of a high sugar diet include;
o Increasing the likelihood of weight gain and obesity
o Negatively affect blood lipid profiles which can increase the risk of CV diseases
o Increasing the risk of developing dental caries
• Bacteria in the mouth metabolize sugars into acids which dissolve the tooth enamel and underlying structure, causing decay, discomfort etc.
• Sticky foods that are high in sugar and adhere to teeth are the most likely to produce dental carries. They include: caramels, licorice, crackers, white bread.
• Sipping fruit juices, soft drinks, and milk throughout the day bathes the teeth in sugar and also increases the risk.
What is lactose intolerance?
Lactose Intolerance:
• Occurs as a result of insufficient lactase or low lactase activity
• Lactose molecules from milk remain, providing food for bacteria in the large intestine.
• Most commonly affects those of Asian, African, Latino/Hispanic backgrounds
• A Lactose intolerance is not a milk allergy
• Milk allergy = immune response to milk protein
• Symptoms include bloating, abdominal discomfort, gas & diarrhea after eating dairy products
Lactose Intolerance: Dietary Implications:
• Individuals who consume little or no milk products are at risk of developing deficiencies for: Calcium, Vitamin D and Riboflavin
• Nearly all lactose deficient individuals can tolerate ½ -1 cup of milk with meals, yogurt, aged cheddar, and acidophilus milk
• Gradual increases in milk intake may cause intestinal bacteria to adapt
• Lactose Intolerance: Alternatives to Milk:
• For Calcium: canned fish with bones, bone soup stock, broccoli, cauliflower, bok choy, calcium fortified beverages, blackstrap molasses, sunflower seeds
• For Vitamin D: 15 minutes exposure to SUNLIGHT several times per week,
fortified margarine, fortified cereals, fatty fish (herring, tuna, salmon, sardines), fortified soy or rice milk
• For Riboflavin: beef, chicken, liver, clams, mushrooms, broccoli, spinach,
egg, breads, fortified cereals.
What is glucose intolerance?
What is epinephrine and cortisol?
Glucose Intolerance:
• Blood glucose must be very closely regulated to provide adequate glucose for body functions and to prevent excessive swings in blood glucose levels
• When blood glucose levels are elevated it is termed as Hyperglycemia
• When blood glucose levels are below normal levels it is termed Hypoglycemia
• Both or either of these can occur with glucose intolerance.
• This complex regulation of the blood glucose levels is performed via the interplay of a number of hormones:
o Insulin
o Glucagon
o Epinephrine (Adrenaline)
o Cortisol
• Low blood glucose levels: stimulate the release of glucagon which:
o Stimulates glycogen breakdown & gluconeogenesis
o Increases blood glucose
• High blood glucose levels stimulate the release of insulin which:
o Stimulates glucose uptake into cells
o Stimulates glycogen synthesis
o Decreases blood glucose
- Epinephrine (a.k.a. adrenalin) and norepinephrine (from the adrenal glands) also trigger a breakdown of glycogen (increasing glucose levels) during times of short term stress (fight or flight response)
- Cortisol also produced in the adrenal glands can also increase glucose levels in response to long term stresses.
