Food & Nutrition Science

Endurance Nutrition: What to Eat Before, During & After Exercise

By: Dr. Bill Misner Ph.D.
Endurance nutrition: how and what to eat before, during and after exercise? Pre-event meal warning: eat 3 hours before exercise.

Both maltodextrin and sugar-based foods have corresponding high glycemic indexes which will elevate blood glucose and insulin release at similar rates. The high glycemic index of sugar and maltodextrin ranges between 90-137. High glycemic carbohydrates such as maltodextrins or simple sugars taken 60 minutes before exercise may have the following less-than-optimal or possibly negative effects on performance: 
  1. Rapid rise in blood sugar raises insulin excess leading to hypoglycemia.
  2. High insulin levels inhibit lipid mobilization during aerobic exercise.
  3. High insulin-induced blood sugar influx into muscle cells causes a higher rate of carbohydrate metabolism, hence rapid carbohydrate fuel depletion.
  4. The pre-event meal hormone insulin-induced blood sugar levels is not effected when ingested 3 hours prior. Hormonal balance is restored 3 hours following a carbohydrate pre-event meal, but is out of metabolic balance if taken within 60 minutes of the start.
  5. The metabolic pathway and caloric donation generated from fructose exclude it completely from consideration as an efficient or required carbohydrate in prior to or after energy expense.

Therefore the pre-event meal should consist of 75-100 grams of carbohydrates from complex carbohydrate maltodextrins but should not be taken closer than 3 hours prior to an exercise event.[1] Intake of high glycemic carbohydrates between meals may be the number one cause of excessive body weight gain in the off season, which may be resolved by either lowering the serving size and frequency of high glycemic carbohydrates or choosing below 50 glycemic indexed high fiber carbohydrate foods:PRE-EVENT MEAL GLYCEMIC INDEX (Pre-Exercise, In between Meals)

GI of 50-59:
Buckwheat, White Spaghetti, Sweet corn, All-Bran, Peas, Yam, Potato Chips.
GI of 40-49:
Wholemeal Spaghetti, Sweet Potato, Navy Beans, Dried Peas, Oranges, Sponge Cake
GI of 30-39:
Butterbeans, Blackeye Peas, Apples, Milk, Yogurt, Tomato Soup
GI of 20-29:
Kidney Beans, Lentils, Parsnips
GI of 10-19:
Soy Beans, Peanuts

During exercise insulin release is inhibited because sympathetic nervous system hormones are released and concurrently exercise augments muscle uptake of glucose from exogenous intake accompanied by lower insulin levels and effects. Low solution sugars (5-8%) or moderate-to-higher solutions (18-24%) maltodextrin (glucose polymers) postpone fatigue efficiently during exercise. The endurance fuel-of-choice is always carbohydrates.

Carbohydrates generate twice the rate of energy as fats when converted into the energy cycle. Proteins donated to the energy cycle from lean muscle mass is limited but constant. Most of the energy fuels required in transition from rest to aerobic energy is initially supplied by stored muscle glycogen in active muscles. During the first hour of submaximal exercise, 50-65% of energy is generated by carbohydrate-glycogen, 30-35% from stored bodyfat, 5-15% from cannibalized lean muscle mass amino acids. However, as exercise continues in 2nd and 3rd hour, lipids from body fat stores are converted, providing 55-65% of the fuels, while glycogen stored carbs provide only 25-35%, and muscle proteins the remaining 5-15%. The rate of protein cannibalization remains fixed, meaning the differences are resolved from lipids and glycogen mobilization. Altering performance at a slower pace demands a larger portion from bodyfat stores while a faster pace increases the rate at which the carbohydrate-glycogen stores are depleted.[1]

For maximal production of energy during athletic activities, the American Dietetic Association supports a nutritional program[2] consisting of 60-65% complex carbohydrates, 10% from protein, and less than 30% from fat. Why are carbohydrates preferred? High muscle glycogen stores support both anaerobic and aerobic activities, which delay fatigue and promote both strength and endurance. There are three types of muscle fibers are recruited during athletic performance, slow twitch, fast-oxidative glycolytic (FOG) and fast twitch. Slow twitch muscle fibers are the high-repetition endurance muscle units that feed on lipid-triglyceride-fats stored within the muscle or transported through the bloodstream. If muscle stores of glycogen are depleted or low, lipid metabolism will not occur efficiently. FOG fibers burn both lipid and muscle glycogen during their employment, while fast twitch burn only muscle glycogen or available blood serum glucose. Optimal performance of each muscle fiber type is supported by a 60-30-10 ratio of carbohydrates-fat-protein ratio of macronutrients. However, the body will in time partially adapt to whatever nutrient composite it is given to work with for endurance demand for movement through time and space.

At 50% maximal aerobic rate or less, the body chooses body fat for energy fuel demands. Fatigue is postponed during the higher 60-80% VO2 Maximal aerobic exercise rate if the athlete ingests a specific carbohydrate solution. These refueling benefits peak at 75% maximal aerobic capacity: (a) Gastric emptying rate is efficient and unimpeded up to 75% VO2 Max rate, (b) Glycogen expense is also most efficient at 75% VO2 Max rate. The human body is able to return approximately 1 gram per minute or 240-280 food calories per hour by way of the liver to refuel the working muscles.[1, 3] Carbohydrate solution strength calls for a body fluid level of osmolality at normal core body temperature. This determines what type and what volume of carbohydrate is absorbed immediately. Athletes may absorb one ounce (28.3 grams) of medium to long-chain maltodextrins diluted in each 3-8 liquid ounces of water, or between 15-20% in solution (fluids:fuel, 3-5:1 weight:weight). This provides a solution at at body osmolality mOsm/l. or less for immediate efficient gastric emptying.

Athletes using the simple sugars sucrose, fructose, or glucose are unaware that simple sugars double the solution osmolality, significantly delaying gastric absorption. When absorption of fuel is delayed due to a high osmolar sugared solutions, fluids and electrolytes must be drawn out of the body then across gastric linings for reducing the high osmolar pressures to body fluid levels for absorption. If a sugared solution is chosen it should be no higher than 6%, which limits the amount of calories that can be absorbed per hour. More calories in the form of longer chain maltodextrins [such as Hammergel] are readily absorbed as high as 18-20% solution. It takes a much greater fluid volume for sugary solutions to meet endurance caloric expense.[1,3, 4, 5]

Noakes suggests that only half of a 120 grams of glucose polymer 20-fluid ounce solution may be metabolized by the liver for return as 60 grams glycogen each hour for application to the energy cycle. For every 60 minutes of aerobic exercise, between 150-225 grams of muscle glycogen is required, while only 60 grams may be returned from fuel-food intake. The body operates at a deficit-spending during endurance exercise. Hence, limited feeding is an example of postponing fatigue. Overfeeding may halt gastric efficiency, while underfeeding will result in premature fatigue. This rationale supports consuming 60-70 grams glucose polymer carbohydrates in solution in 3-4 divided doses of 16-24 fluid ounces each hour during endurance events.[4]:

IN LIVER[g/kg]
Trained Low Carbohydrate Diet
Trained High Carbohydrate Diet
Trained 24-Hour Fast
Trained Glycogen Stripping
[3 day low Carbohydrates during training]
Trained [3 day high Carbohydrate Loading]
Trained [After 3-4 hours Intense 70-85% VO2 Max Rate]
Trained 24 hours post-race[high CHO]
Trained 48 hours post-race[high CHO]
Trained 7 days post-race[high CHO]

Short lived is the fate of high carbohydrate intake storage proportionate to exercise intensity and duration. However, consuming a high percentage of carbohydrate-rich foods(CHO) is a must-do for maintaining a high-constant energy flow from these most efficient of the stored combustible fuels designed to fight off fatigue, feebleness, or muscle-failure. Just eating lots of carbs is not the answer, but timing, selection, and balance must be considered in your choice of food, liquid, and electrolytes. In addition, hidden factors exist specific to each athlete’s calculation for how their body responds to extreme endurance are equally important to training both the cardiovascular system and the muscles.

At least eight hidden hindrances or help factors should be considered as a predicted model for completing such a demanding performances:


  1. Athlete’s individual gastric volume tolerances: 400 to 800 ml avg. range. (Hindered by drinking more than 900 ml/hour. May result in Dilutional Hyponatremia)
  2. Solution osmolality at 280-300 mOsm or less. (Hindered by slow absorption of simple sugars doubling solution osmolality)
  3. Solution temperature at 41 degrees F. (Hindered by a warm solution being absorbed slowly at a 39% rate compared to 100% of colder solutions)
  4. Caloric content absorption rate. (Simple Sugars vs. Complex Carbohydrates) (Hindered by lower caloric volume absorbed from Simple Sugars in comparison to larger volumes absorbed from complex carbohydrates)
  5. Aerobic rate of pace from 55-75% VO2 Max. (Hindered by speed, speed kills: the faster you go, the faster carbohydrate stores are depleted)
  6. Environmental temperature and humidity: Slow down in heat![6] (Hindered when body core temperatures exceed 103 degrees, i.e. when the outside temperatures and humidity cause core body temperatures to rise above 102, efficiency deteriorates proportionately. When core temperatures are 100-102, core temperature is suggested as “optimal” for the max-efficiency burning rate of muscle glycogen stores. NOTE: When perspiration first appears on the brow, core body temperature is 102 degrees.)
  7. Individual fitness and acclimatization (hindered by lack of acclimatization or fitness training affects performance by up to 50 percent! The same fit athlete finishing the event in 8 days would otherwise finish the event in 12 days in an unfit-unacclimatized state. The fit, acclimatized athlete requires only 50% of the electrolyte stores of an unfit, unacclimatized athlete and has higher tissue buffering and enzymatic capacities for efficient endurance energy production)
  8. Age, gender, body mass index. (Hindered by genetic capacity, hormone mechanics prevalent to gender favor the most lean muscle mass to body fat ratio specimen. Age also may be a factor, favoring youth, another cause for variable responses to the rate of carbohydrate intake upon its oxidation rate in the working muscles.)

Timing 240-280 calories of carbohydrates in an osmolar solutions (280-303 mOsm or less) in 16-24 fluid ounces during a 50% VO2 Max to no higher than 75% VO2 maximal aerobic exercise rate per each hour during exercise is supported from the literature to postpone endurance-induced fatigue. This general principle works metabolically to maximize endurance performance in 99% of those competing in prolonged athletic events even in extreme conditions.[1, 3, 4, 5, 7]GLYCEMIC INDEX FOR POST-EXERCISE MUSCLE SYNTHESIS RECOVERY
Glycemic index is typically based on the standard score of 100 from measured blood glucose levels resulting from eating 50 grams of glucose or white bread. Athletes should eat low glycemic carbohydrates before exercise. Eating moderate-to-high glycemic carbohydrates after exercise, during the 2-hour window post-depletion enhances glycogen restoration, while carbohydrate-induced body fat gain is minimized if dose-frequency is controlled limiting the volume of higher glycemic sugars or moderately high glycemic foods. Why? After exercise, when the hormone insulin is low and exercise-induced catecholamines are high, the glycogen-storing enzyme-activate, Glycogen Synthetase, replenishes depleted glycogen from intake of dietary moderate-to-high glycemic indexed carbohydrates. This occurs at an optimal rate of 50-75 grams carbohydrate per hour up to a maximum of 500 carbohydrate grams. After muscle glycogen stores are depleted, restoration occurs at the rate of 5-7% per hour. The initial post workout meal recommended contains 4 portions of carbohydrates to 1 part complete protein from soy, whey or egg whites. This formula is suggested to enhance both muscle synthesis substrates and glycogen stores after an intense depletion workout. A post workout repletion meal needs to be low-fat, since fat slows digestion and absorption rate significantly.

The only time a large glucose rise is recommended is during the 2-hour window post-workout. The largest glucose rises from food categories are from vegetables-(70), followed by breakfast cereals-(65), cereals and biscuits-(60), fruit-(50), dairy products-(35), and dried legumes-(31):

[post & 60′ pre-exercise]
[pre-exercise & in between meals]
Glucose 100
Orange Juice 57
Apple 36
Baked Potato 85
White Rice 56
Pear 36
Corn Flakes 84
Popcorn 55
Skim Milk 32
Cheerios 74
Corn 55
Green Beans 30
Graham Crackers 74
Brown Rice 55
Lentils 29
Honey 73
Sweet Potato 54
Kidney Beans 27
Watermelon 72
Banana 50
Grapefruit 25
Bread/Bagel 70-72
Orange 43
Barley 25
Table Sugar 65
Apple Juice 41
Raisins 64

For more on food glycemic index, see Rick Mendosa’s Glycemic Index List.[8] If the endurance athletes adapt to a lower consumption and timing intake of high glycemic carbohydrate sources while raising the dietary low glycemic index foods, both glycogen stores increase while bodyfat dead weight decreases resulting in an optimal performance.


  1. McArdle WD, Katch FI, Katch VL, EXERCISE PHYSIOLOGY, Williams & Wilkins, Baltimore, Md., 4th Edition, 1996:72-77.
  2. American Dietetic Association Website
  3. Coggan A.R., Coyle E.F., Effect of carbohydrate Feedings During High Intensity Exercise, Journal of Applied Physiology, 1988; 65:1703-1709.
  4. Noakes T.D., Rehrer N.J., Maughn R.J., The Importance of Volume in Regulating Gastric Emptying, Medicine and Science in Sports and Exercise, 23(3)1991 & Noakes TD, [a listing 25+ key search studies], THE LORE OF RUNNING, Leisure Press, Champaign, Illinois, 1991: 115-117.
  5. Ahlborg G, Felig L, Lactate and glucose exchange across the forearm, legs and splanchnic bed during and after prolonged exercise, Journal of Clinical Investigation, 1982, 69:45-54.
  6. Buono MJ, Heaney JH, Leichliter SG, Vurbeff GK., Acclimation to humid heat reduces resting core temperature but not heat storage, Medicine and Science in Sports and Exercise, 1997; 29(5), Supplement abstract 560.
  7. Verde, T., et al., Sweat Compostion in Exercise and Heat, JOURNAL OF APPLIED PHYSIOLOGY, 1982 ;53(6):1541-1543.
  8. Rick Mendosa’s Glycemic Index List


Associate Editor, Metabolic Responses to Exercise Journal of Exercise Physiology-online

Dolezal & Associates Publishing, Livermore California, 1998.

Dr. Bill Misner, Ph.D. is the Director of Research and Product Development for E-CAPS INC. & HAMMER NUTRITION LTD., supplement anufacturers specializing in fuels, substrates, and supplements for endurance athletes. Dr. Misner published NUTRITION FOR ENDURANCE:FINDING ANOTHER GEAR, Dolezal & Associates Publishing, Livermore, Calif. 1998.
This article is reprinted by permission:
Dr. Bill Misner, Ph.D.


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