Ex. 6 L1 - Macronutrients (L-58) Flashcards
Role of dietary carbohydrates
-Major energy source for humans
(4 kcal/g)
-Used to generate many metabolic intermediates
Excess carbohydrates are converted to
Glycogen
Triacylglycerol
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
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
Complex carbohydrates
-Polysaccharides
-Many monosaccharides linked together in chain
-Glycogen in animals and starch and fiber in plants
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
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
a-amylase
Hydrolyzes starch and glycogen to maltose and maltotriose
Exists in saliva and pancreatic juice
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
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
Raffinose
Oligosaccharide in leguminous seeds (beans and peas)
Cannot be hydrolyzed by human enzymes
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
Dietary fibers
Cellulose and hemicellulose
Lignin
Pectin
Cellulose and hemicellulose
Unrefined cereals, bran, whole wheat
Insoluble
Increase stool bulk and decrease intestinal transit time
Lignin
Woody parts of vegetables
Insoluble
Binds cholesterol and carcinogens
Pectin
Fruits
Soluble
Decreases rate of sugar uptake and decreases serum cholesterol
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
