Carbohydrate molecules made up of mono-, di- tri- and poly-saccharides multi-hydroxylated 5- (ribose) and 6-carbon (glucose, fructose, galactose ...) cyclic molecules. Some monosaccharides
Mammals store glucose as glycogen (humans store approximately 350g in muscle; 90 g in liver) Plants store glucose as starch, build cellulose for structure
Body “Stores” of Energy Tissue Stores ~g Days Days Minutes Starvation Walking Marathon Running Adipose TG 9,000 34 10.8 4,018 Liver Glycogen 90 0.15 0.05 18 Muscle Glycogen 350 0.6 0.2 71 Blood Glucose 20 0.03 0.01 4
Carbohydrates primary NRG source for C&PNS NRG for moderate/stressful activities ribose/deoxyribose (RNA/DNA/ATP…) muccopolysaccharides (mucus/synovial) glycoproteins (cell membranes) D-galactosamine (collagen/cartilage)
DRI 130 g/day 45% to 65% of total calories (4 kcal/g) IOM recommend 1 hour of moderately stressful exercise every day NRG for moderately stressful exercise is 50 – 80% carbohydrate . . . 6 – 7 mph ~ 600 – 800 kcals @ 50% ~ 300 – 400 kcals ~ 75 – 100 g additional CHO Therefore, a logical minimum DRI would be more than the IOM recommendation ~ 200g/day would be a reasonable estimate
- Mastication in mouth Bolus w/ saliva/mucus Salivary α-amylase • Pancreatic enzymes pancreatic α-amylase • Brush border saccharidases: maltase sucrase lactase
Carbohydrates are “transported to the liver” through the portal vein and are picked up by the liver (and the rest of the body’s cells for those that the liver doesn’t get) for processing . . . Liver stores glucose as glycogen (so does the kidney) & releases glucose to the venous circulation and it is transported to the rest of the body through the arterial circulation . . . . . . . . . .
Regulation of glucose levels in the blood is very important Normal Fasting (Serum) ~ 70 – 100 mg/dl Elevated = Diabetes Low = Hypoglycemia Insulin from pancreas stimulates uptake of glucose into muscle cells by activating the GLUT4 transporter. When serum levels of glucose decrease too much, then the pancreas releases glucagon to stimulate the liver and kidney to break down glycogen to glucose and release glucose into the blood (glycogenolysis). Adrenals will release cortisol if levels stay too low to enhance breakdown of protein in muscles to release amino acids so the liver can pick up the amino acids and make them into glucose (gluconeogenesis). From the carbohydrate/diet standpoint, after eating a meal, glucose levels increase in the blood and trigger an insulin response. Chronic increases in insulin can greatly increase the risk for developing Type II diabetes. Eating foods that produce a large increase in insulin tend to be more risky for diabetes than eating foods that do not stimulate a large increase in glucose levels.
Glycemic Index and Glycemic Load: Glycemic Index: A relative measure of how rapidly the digested carbohydrate appears in the blood as glucose relative to the same amount of pure glucose over time. A 50 g amount of glucose would have a GI of 100 while a 50g amount of other carbohydrate sources would be expressed relative to the glucose GI. GI is 70 or more is high GI of 56 to 69 is medium GI of 55 or less is low.
Glycemic Index and Glycemic Load: Glycemic Load: A measure of total amount of glucose appearing in the blood over time based on the total amount of digestible carbohydrate in the food. GL = GI / 100 x g GL of 20 or more is high GL of 11 to 19 is medium GL of 10 or less is low Because some high GI foods may contain relatively little total carbohydrate (or visa versa), calculating a glycemic load based on both GI and total CHO can make sense: Wonder enriched white bread: GI = 73, GL = 10 . . . Betty Crocker chocolate cake: GI = 38, GL = 20 . . .
GL / GI per serving of some common foods (adapted from: http://www.mendosa.com/glists.htm) Low GI Medium GI High GI - 55 56 - 69 70 – 100 Grapes 8 / 46 Pineapple 7 / 59 Watermelon 4 / 72 Low Apples 8 / 42 Cantaloupe 4 / 65 Popcorn 8 / 72 GL Peanuts 1 / 14 Beets 5 / 64 Wheat bread 8 / 71 0 - 10 Corn 9 / 54 Sugar 7 / 68 White bread 10 / 70 Baked beans 7 / 48 Rye bread 8 / 58 Waffles 10 / 76 Honey 10 / 55 Bananas 12 / 52 Life cereal 16 / 66 Cake donuts 17 / 76 Medium Navy beans 12 / 38 Potatoes 12 / 57 Cheerios 15 / 74 GL Sourdough bread 15 / 54 Wild rice 18 / 57 Shredded wheat 15 / 75 11 - 19 Parboiled rice 17 / 47 Sweet potatoes 17 / 61 Gatorade 12 / 78 Apple juice 12 / 40 Coca Cola 16 / 63 Bran flakes 13 / 74 High Linguine 23 / 52 Couscous 23 / 65 Baked potatoes 26 / 85 GL Macaroni 23 / 47 White rice 23 / 64 Cornflakes 21 / 90 20+ Spaghetti 20 / 42 Power bar 24 / 56 Dried dates 42 / 103 Note that “complex carbohydrates” form the basis of both high glycemic and low glycemic foods; indicating that the simplified concept that “complex carbohydrates” are better than “simple carbohydrates” doesn’t make a lot of sense. Another “note”: when eaten in combinations, then the GI/GL is completely different than the tabled values indicating that actually applying the GI/GL information to a mixed-diet is essentially impossible…