Dietary Issues in Exercise MetabolismCarbohydrate Supply

Tissue Stores ~g ~ Days ~ Days ~ Minutes Starvation Walking Marathon

Running

Adipose TG - all 9,000 34 10.8 4,018

muscles 7 - 14 g/kg @ ~ 20 - 30 kg muscles = 140g – 420 g

0.25 – 0.75 90 - 270

Liver Glycogen 90 0.15 0.05 18

Muscle Glycogen 350 0.6 0.2 71

Blood Glucose 20 0.03 0.01 4

Remember this . . .

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 highGI of 56 to 69 is mediumGI 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 highGL of 11 to 19 is mediumGL 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 / 72Low Apples 8 / 42 Cantaloupe 4 / 65 Popcorn 8 / 72GL Peanuts 1 / 14 Beets 5 / 64 Wheat bread 8 / 710 - 10 Corn 9 / 54 Sugar 7 / 68 White bread 10 / 70

Baked beans 7 / 48 Rye bread 8 / 58 Waffles 10 / 76Honey 10 / 55

Bananas 12 / 52 Life cereal 16 / 66 Cake donuts 17 / 76Medium Navy beans 12 / 38 Potatoes 12 / 57 Cheerios 15 / 74GL Sourdough bread 15 / 54 Wild rice 18 / 57 Shredded wheat 15 / 7511 - 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 / 85GL Macaroni 23 / 47 White rice 23 / 64 Cornflakes 21 / 9020+ Spaghetti 20 / 42 Power bar 24 / 56 Dried dates 42 / 103

Dietary Recommendations For Maximum PerformanceIn “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) 3 - 4 hours prior to exercise . . .

~ 2 - 3 g / kg?

- Consumption of low-GI carbohydrates 30 - 60 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 . . .- 60 grams / hour may be optimal- GI is probably not important . . .- a 4 – 8% sucrose (or glucose) solution works very well . . .

- 800 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%)POWERade 8 oz. = 17 g CHO (7%)

Or drink water and use:Gu Energy Gel 32 g = 25 g CHOPower Bar 1 bar = 20 g CHO

Dietary Recommendations For Maximum Performance In “Long Duration” Endurance Events (T >1 hour) During the Event

Effect of Carbo’ LoadingAnd Carbo’ FeedingOn 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 / hourMuscle Glycogen ~ 350 g = ~ 1400 kCal = 560 kCal / hourGluconeogenesis ~ 3 - 4 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 CHOconsumption / hour = ~ 240 kCal / hour

= ~ 960 kCal / hour= glycogen depletion before finishing

Add in Carbohydrate LoadingLiver Glycogen ~ 110 g = ~ 440 kCalMuscle Glycogen ~ 450 g = ~ 1800 kCal

= ~ 2240 kCal = ~ 896 kCal / hour + 240 kCal from consumption= ~ 1136 kCal / hour= no glycogen depletion before finishing

Dietary Recommendations For Maximum PerformanceIn “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 - 150 g or 1.5 g / kg body weight)

-Include some protein to maximize glucose and amino acid uptake as well asmaximize protein synthesis (10 g – 20 g high quality protein)