Ex. 6 L1 - Macronutrients (L-58) Flashcards by Jenna Tapper

Role of dietary carbohydrates

-Major energy source for humans
(4 kcal/g)
-Used to generate many metabolic intermediates

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Excess carbohydrates are converted to

Glycogen
Triacylglycerol

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Which organs can store glycogen

Liver and muscle
-Muscle can store glycogen

-All other carbohydrates will eventually make fat and then store it as a triacylgylcerol

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Simple Carbohydrates

Sugars
Fruits, vegetable, and milk
Monosaccharides
-Single sugar molecules (C6H12O6)
Glucose, fructose, galactose
NOT COMMONLY OBSERVED IN FOODS - usually parts of disaccharides
Disaccharides
-Two sugar molecules combined
Glucose and fructose
-Sucrose lactose, maltose

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Complex carbohydrates

-Polysaccharides
-Many monosaccharides linked together in chain
-Glycogen in animals and starch and fiber in plants

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Glucose

AKA Dextrose
-The most important carbohydrate fuel for the body
-Frequently referred to as blood sugar
-Rarely occurs as monosaccharide in food; part of a disaccharide

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Fructose

Found in fruits and vegetables, more than half the sugar in honey
-Does not cause as great a rise in blood glucose as other sugars, but causes an increase in blood lipids
-The dramatic increase in the use of high-fructose corn syrup has been suggested to be related in the increased incidence of diabetes and obesity

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a-amylase

Hydrolyzes starch and glycogen to maltose and maltotriose
Exists in saliva and pancreatic juice

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Enzymes on the luminal surface of small intestine

-Maltase (a-glycosidease): maltose and maltotriose -> glucose
-Sucrase: sucrose -> glucose and fructose
-Lactase: Lactose-> glucose and galactose
-Lactose intolerance occurs when lactase is not produced enough
Only monosaccharides are absorbed in the body

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Indigestible carbohydrates

-Converted to monosaccharides by bacterial enzymes
-Metabolized anaerobically by bacteria
-Result in production of short-chain fatty acids, lactate, H2, CH4 and CO2
-May cause flatulence and abdominal discomfort

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Raffinose

Oligosaccharide in leguminous seeds (beans and peas)
Cannot be hydrolyzed by human enzymes

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Glycemic Index

Measure of how quickly individual foods will raise blood glucose levels
Defined as the ratio of the area of the blood glucose response curve to that of glucose

Lower GI = longer time to absorb in the body
When high GI = lots of insulin released

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Dietary fibers

Cellulose and hemicellulose
Lignin
Pectin

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Cellulose and hemicellulose

Unrefined cereals, bran, whole wheat
Insoluble
Increase stool bulk and decrease intestinal transit time

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Lignin

Woody parts of vegetables
Insoluble
Binds cholesterol and carcinogens

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Pectin

Fruits
Soluble
Decreases rate of sugar uptake and decreases serum cholesterol

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Lipids in diet

Efficient source of energy (9kcal/g)
Provides satiety
Adds flavor and aroma to diet
Carrier for fat-soluble vitamins
Traicylglycerol is >90% of dietary fat
-Glycerol + three fatty acids
Phospholipids, cholesterol, cholesterol esters, fatty acids are <10% of dietary fat

Essential fatty acids

Omega-3 (w3) fatty acids
a-Linolenic acid (18:3) in vegetable oils
-Eicosapentaenoic acid (EPA) (20:5) and docosahexaenoic acid (DHA) (22:6) in fish oils

-Omega-6 (w-6) fatty acids
Linoleic acids (18:2) in corn oil
Arachidonic acid (20:4) in meat and fish
-Used to synthesize eicosanoids in the body
-Deficiency is rare in US; need to be added to artificial infant formula
-The ratio of w-3 to w-6 acids in the diet is important in regulating processes like blood pressure, blood clotting, and immune function

Trans fatty acids

Most unsaturated fatty acids found in nature have Cis double bond configuration
-Hydrogenation process to convert unsaturated fatty acids to sat fatty acids produces trans fatty acids as byproducts
-Hydrogenated or partially hydrogenated vegetable oils are a primary ingredient in margarine and shortening
-A trans fatty acid has a higher melting point than the same fatty acids in the cis configuration
-Tran fats raise blood cholesterol levels and increases the risk of heart disease

Digestion of lipids

Fats need to be solubilized for digestion
-Dispersion of lipid phase into small droplets
-Solubilization by bile acids

Gastric and pancreatic lipases
-Hydrolyze triacylglycerol to fatty acids and monoacylglycerol
-Produced fatty acids acts as surfactants

Esterase
-Hydrolyzes monoacylglycerol and cholesterol ester

Utilization of lipids

Chylomicron delivers lipid to peripheral tissues directly
-Muscle uses fat as energy source
-Excess fat is stored in adipose tissues
-Brain does not use fat as energy source
-When starved, liver converts fatty acid to ketone bodies (ketogenesis), which are utilized as energy source by brain and muscle

Role of dietary proteins

Essential Structural component
Enzymes, hormones, plasma proteins, antibodies

Excess protein

Source of energy
Glucogenic amino acids -> glucose
Ketogenic amino acids -> keto acids and fatty acids
-Eventually converted to triacylglycerol in adipose tissue

protein = 20% of our body weight

Negative nitrogen balance

Inadequate dietary intake of protein
Trauma or illness

Positive nitrogen balance

Net increase in body protein stores Growing children, pregnant women, or adults recovering from illness

Essential amino acids

Cannot be synthesized by the body or synthesized but not enough (arginine, methionine, and phenylalanine) If not in the diet, new proteins cannot be made w/o breaking down other body proteins -> **negative nitrogen balance** occurs Mixed sources of protein necessary for vegetarian diet Essential: -Arginine -Histidine -Isoleucine -Leucine -Lysine -Methionine -Phenylalanine -Threonine -Tryptophan -Valine

Conditionally essential amino acids

If phenylalanine is not enough, tyrosine can not be made enough in the body Conditionally: Cysteine Glutamine Glycine Proline Tyrosine

Gastric digestion of proteins

pH of gastric juice <2 Low pH denatures proteins Pepsins - stable and active at acidic pH; aspartic protease

Intestinal digestion of proteins - Peptidases at luminal surface

-Brush border - luminal surface of epithelial cells -Rich in peptidases -Produces free AA and di and tripeptides

Intestinal digestion of proteins - intracellular peptidases

Amino acid and peptide transport systems Intracellular hydrolysis of di and tripeptide s Practically **only free amino acids are released to blood**

Celiac disease

**Celiac sprue** -Gluten intolerance -~2 million ppl in US -Autoimmune disorder in genetically predisposed individuals Caused by exposure to gluten -Major proteins contained in wheat, rye, and barley The lining of the small intestine is inflamed and damaged -Diarrhea, weight loss, malnutrition -Life-long gluten-free diet

Dietary Composition

Average consumption (US; Male) -Carb - 310g -Fat - 94g -Protein - 100g Energy content: 4kcal/g Fat: 9kcal/g Protein 4kcal/g Alcohol 7kcal/g

Energy reserves of humans

Excess energy is stored mostly as **fat** in adipose tissue Glycogen in the liver to maintain blood glucose levels Glycogen in muscle is used for **exercise** **Protein is not a preferred energy reserve**

Fuel reserves

Glycogen in liver: 70g; 280kcal Glycogen in muscle 120g; 480kcal Glucose in Body fluids 15,000g; 135,000kcal Fat in adipose 15,000g; 135,000kcal Protein in muscle 6,000g; 24,000kcal

Well-fed state

**Insulin** release **Glycolysis** Glycogen synthesis Catabolism of amino acids Fatty acid synthesis No gluconeogenesis ( = no Cori Cycle)

Early fasting state

**Glucagon** release Glycogen breakdown **Gluconeogenesis** -Cori cycle -Alanine cycle No catabolism of amino acids

Fasting state

Glucagon release **Gluconeogenesis** -Protein is used as a major carbon and nitrogen source -Alanine -Glutamine Lipolysis in adipose tissue Fatty acid oxidation **Ketogenesis** Reduced thyroid hormones -> the daily basal energy requirement drops by 25%

Caloric homeostasis

Constant availability of fuels in the blood Glucose is **carefully regulated** If glucose is <1.5mM (27mg/dL), coma and death will follow shortly **Hyperglycemia** -> dehydration, hyperglycemic coma, complications of diabetes

Glucose ATP equivalents

Very well fed: 6.1mM 110mg/dL 313mM (ATP) Postabsorptive 12h 4.8mM 86mg/dL 290 mM (ATP) Fasted 3 days 3.8 mM 68mg/dL 380 mM (ATP) Fasted 5 weeks 3.6 mM 65mg/dL 537mM (ATP)

Energy for brain

Glucose as brain food -Brain uses more than **20% of total energy** -100-120g of glucose per day (preferred fuel) -Uses 15-20% of the total oxygen -Constant energy need (awake or sleep) Membrane potential -Na+/K+ ATPase No energy storage -No glycogen storage -Brain does not use fat Adaptation to starvation **Ketone bodies made from acetyl-CoA in the liver**

Marasmus

Inadequate intake of both protein and energy Thin, wasted appearance Small for his/her age -Infants and young children -Reduced ability to fight off infection

Kwashiorkor

Inadequate intake of PROTEIN WITH ADEQUATE ENERGY INTAKE Mainly in children 1-3 years Deceptive plump appearance due to edema