Dietary Issues in Exercise Metabolism Carbohydrate Supply

Tissue Stores ~g ~ Days ~ Days ~ Minutes StarvationWalkingMarathon Running Adipose TG - all 9, ,018 muscles ~ kg muscles = 140g – 420 g 0.25 – Liver Glycogen Muscle Glycogen Blood Glucose Remember this...

... and this...

Moderately stressful endurance exercise: As a result of continuous muscle contraction, all metabolic pathways of ATP generation increase while those of storage and synthesis decrease... Because the glycolysis pathway increases so much faster than the others, glycogen stores in the muscle will decrease more quickly than TG stores... increasing the dependence of muscles on plasma supplies of substrates... a hormonal issue resulting in this:

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 = Betty Crocker chocolate cake: GI = 38, GL = 20...

GL / GI per serving of some common foods (adapted from: Low GIMedium GIHigh GI – 100 Grapes 8 / 46Pineapple 7 / 59Watermelon 4 / 72 LowApples 8 / 42Cantaloupe 4 / 65Popcorn 8 / 72 GLPeanuts 1 / 14Beets 5 / 64Wheat bread 8 / Corn 9 / 54Sugar 7 / 68White bread 10 / 70 Baked beans 7 / 48Rye bread 8 / 58Waffles 10 / 76 Honey 10 / 55 Bananas 12 / 52Life cereal 16 / 66Cake donuts 17 / 76 MediumNavy beans 12 / 38Potatoes 12 / 57Cheerios 15 / 74 GLSourdough bread 15 / 54Wild rice 18 / 57Shredded wheat 15 / Parboiled rice 17 / 47Sweet potatoes 17 / 61Gatorade 12 / 78 Apple juice 12 / 40Coca Cola 16 / 63Bran flakes 13 / 74 HighLinguine 23 / 52Couscous 23 / 65Baked potatoes 26 / 85 GLMacaroni 23 / 47White rice 23 / 64Cornflakes 21 / Spaghetti 20 / 42Power bar 24 / 56Dried dates 42 / 103

Dietary Recommendations For Maximum Performance In “Long Duration” Endurance Events (T >1 hour) Prior to Event - Consumption of high GL low GI carbohydrate meals for 3 to 4 days before competition (with taper: no more stressful workouts)... ~ 10 g / kg / d? - Consumption of a high GL low GI-carbohydrate meal (200 g – 300 g CH) hours prior to exercise... ~ g / kg? - Consumption of low-GI carbohydrates minutes prior to exercise... ~ 1 g / kg?

-Consume 400 ml to a maximum of 800 ml water per hour during the exercise... - (Tim Noakes, International Marathon Medical Directors Assoc. – I support this…) -Consume maximum amount water tolerated - (ACSM Position Stand – I don’t really support this…) - Consume 30 to 60 grams carbohydrate per hour during long-duration grams / hour may be optimal - GI is probably not important... - a 4 – 8% sucrose (or glucose) solution works very well ml/hr of 8% = 64 g/hr Make your own or buy the stuff: Hydrade:8 oz.=10 g CHO (4%) Gatorade:8 oz.=14 g CHO (6%) Accelerade:8 oz.=14 g CHO (6%) POWERade8 oz.=17 g CHO (7%) Or drink water and use: Gu Energy Gel32 g=25 g CHO Power Bar1 bar=20 g CHO Dietary Recommendations For Maximum Performance In “Long Duration” Endurance Events (T >1 hour) During the Event

Effect of Carbo’ Loading And Carbo’ Feeding On Glycogen Supply

Carbohydrate Use During A Hypothetical Marathon Race Racing a marathon in ~2.5 hours = ~ 2700 kCal required = ~ 1080 kCal / hour at ~ 90% CHO use at racing speed= ~ 972 kCal / hour from CHO (~243 g / hour) Liver Glycogen~ 90 g = ~ 360 kCal = 144 kCal / hour Muscle Glycogen~ 350 g= ~ 1400 kCal = 560 kCal / hour Gluconeogenesis~ g / hour= ~ 7.5 – 10 g = 12 – 16 kCal / hour Total = ~ 1800 kCal = ~ 720 kCal / hour from CHO = glycogen depletion before finishing Add in max of 60 g CHO consumption / hour = ~ 240 kCal / hour = ~ 960 kCal / hour = glycogen depletion before finishing Add in Carbohydrate Loading Liver Glycogen~ 110 g = ~ 440 kCal Muscle Glycogen~ 450 g= ~ 1800 kCal = ~ 2240 kCal = ~ 896 kCal / hour kCal from consumption = ~ 1136 kCal / hour = no glycogen depletion before finishing

Dietary Recommendations For Maximum Performance In “Long Duration” Endurance Event (T >1 hour) After the Event - Consume high GI carbohydrate within 1 hour after exercise to maximize recovery of muscle glycogen (100 g g or 1.5 g / kg body weight) -Include some protein to maximize glucose and amino acid uptake as well as maximize protein synthesis (10 g – 20 g high quality protein)