If the average athlete took in no replacement calories, a female would lose 10.5 pounds, and a man would lose nearly 13 pounds from body fat or lean muscle mass stores.

Fuel Required Energy Demands May Or May Not Exceed Intake
The human body can return only around 240 food calories per hour by way of the liver to refuel working muscles. The muscle carbohydrate oxidation rate has been measured at a rate between 60 to 70 grams of carbohydrate per hour. [1] This rate results in 5000 fuel-to-energy calories extracted from foods eaten each day, reducing the overall eight-day fuel requirements by negative 40,000 calories.

This number exceeds the female athlete's need by adding 13.6 ounces body fat, though it leaves the man well short (by 4,848 calories), for a loss of negative 1.38 pounds body fat.

What is the Ideal Fuel?
The selected fuel-of-choice is always carbohydrates. Carbohydrates generate twice the rate of energy as fats converted into the energy cycle. Protein fuels donated to the energy cycle from lean muscle mass are limited but constant. Most of the energy fuel required in transition from rest to aerobic energy is supplied by stored muscle glycogen from active muscles.

During the first hour of sub-maximal exercise, 50 to 65 percent of energy comes from carbohydrates, 30 to 35 percent from lipids, 5 to 15 percent from lean muscle mass protein. As exercise continues into the second and third hours, lipids from body fat stores are converted to energy at 55 to 65 percent, carbohydrates at 25 to 35 percent, and muscle proteins at 5 to 15 percent. The rate of protein cannibalization remains fixed between 5 to 15 percent for its caloric contribution to energy, making up the difference in lipid or carbohydrate demand. Altering to a slower rate of pace involves a larger portion of stored lipids. A faster pace increases the rate at which carbohydrate or glycogen stores are depleted.

For maximal production of energy during athletic activities, the American Dietetic Association claims research supporting a nutritional program that consists of 60 to 65 percent from complex carbohydrates,10 percent from protein, and less than 30 percent from fat. [2] Why so much carbohydrates? High muscle glycogen stores support both anaerobic and aerobic activities, which delay fatigue and promote both strength and endurance.

Three types of muscle fibers are recruited during athletic performance: slow twitch (ST), fast-oxidative glycolytic (FOG)and fast twitch (FT). ST 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 FT's 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 adapt to whatever nutrients it is given to work with for endurance demand for movement through time and space.

Proposal Rationale for the Best Fuel
Ideally, the Eco-Challenge athlete would dilute one ounce (28.3 grams) of long-chain complex carbohydrates in each five to eight liquid ounces of water, or roughly a 20 percent solution (fluids:fuel would be 5:1 by weight), to provide mOsm at body fluid osmolality of 280-300 mOsm/l for optimal fuel-and-fluid gastric emptying.

Some athletes using simple sugars, sucrose, fructose, or glucose are unaware that simple sugars may double the osmolality, which significantly delays 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) across gastric linings in order to reduce the osmolar pressures for transition of much needed fluids and fuels for working muscles. If a sugared solution is chosen, it should be no higher than five to six percent, while long chain maltodextrins may be readily absorbed at up to a 15 to 20 percent solution. But take heed, it will take a much greater fluid volume of sugary solutions to meet the caloric expense of either our subjects, for both male and female athletes.

Why avoid the simple sugar solutions? Take a look at the numbers:

Type of Fuel       Calories Provided at 280-300 mOsm. Osmolality
Glucose            0.2  cal/ml
Fructose           0.2  cal/ml
Sucrose            0.4  cal/ml
Complex Carbs      1.0+ cal/ml

Gastric emptying rates are affected by stomach volumes, ranging from 400 ml to 800 ml. Some athletes tolerate significantly higher stomach volumes than others. As noted here, one athlete tolerated 50 percent stomach volume of the other. In a 10-minute period of time, athletes were observed to empty stomach volumes at the following rates: [3]

1-Pure Water Solution 65 percent
  (From 400 ml, 260 ml was emptied-From 800 ml, 520 ml emptied)
2-Isotonic 7 percent Carbohydrate Solution-50 percent
  (From 400 ml, 200 ml was emptied-From 800 ml, 400 ml emptied)
3-Glucose 15 percent Solution-25 percent
  (From 400 ml, 100 ml was emptied-From 800 ml, 200 ml emptied)
4-Maltodextrin 18 percent Solution-25 percent
  (From 400 ml, 100 ml was emptied-From 800 ml, 200 ml emptied)

What Enhances or Hinders Carbohydrates [CHO] Absorption Rate?
Experts suggest that approximately 600 ml of fluid per hour, with up to 120 grams from a glucose polymer energy drink will adequately convert 50 percent of a complex carbohydrate drink (60 grams of the glucose polymer solution) transferred into the energy cycle of oxidized exogenous CHO (foods) processed by the liver to working muscles. There are, of course, different dietary interventions known and shown to dramatically effect muscle and liver glycogen (carbohydrate) stores [4]:

Subjects    Type And Time Of Diet    In Muscle[G/Kg]  In Liver[G/Kg]
Trained     Low Carbohydrate Diet    14               30
Trained     High Carbohydrate Diet   21               70
Trained     24-Hour Fast             21               10
Trained     Glycogen Stripping       10                7
            (3 day low Carbohydrates 
            during training)
Trained     (3 day high Carbohydrate 36               90
            Loading)   
Trained     (After 3-4 hours Intense 
            70-85 percent VO2 Max Rate) 4+            23
Trained     24 hours post-race 
            (high CHO)               15               90
Trained     48 hours post-race 
            (high CHO)               27               90
Trained     7 days post-race 
            (high CHO)               30               90

The fate of high carbohydrate intake stores - proportionate to exercise intensity and duration - is short lived. But eating a high percentage of carbohydrate-rich foods is a necessity in order to maintain a constant energy flow.

So is eating a lot of carbohydrates the secret to success? Yes and no, as certain balances must be considered for intake of food, liquid, and electrolytes. Each race participant must calculate these hidden factors, and how their body responds to extreme endurance demands.

Eight hidden variables should be considered as a predictive model for completing such a demanding course:

1. Athlete's individual gastric volume tolerances - 400 to 800 ml average range. Hindered by: Drinking more than 900 ml per hour, which may result in Dilutional Hyponatremia.

2. Solution Osmolality - 280-300 mOsm. Hindered by: Slow absorption of simple sugars, which doubles solution osmolality.

3. Solution Temperature - 41 degrees Fahrenheit. Hindered by: A warm solution being absorbed slowly, at a 39 percent rate compared to 100 percent 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 to 75 percent VO2 Max. Hindered by: Speed. The faster one travels, the faster one's carbohydrate stores are depleted.

6. Environmental Temperature and Humidity: Slow Down in Heat. Hindered by: Body core temperatures exceeding 103 F. When the outside temperatures and humidity cause core body temperatures to rise above 102 F, efficiency deteriorates proportionately. When core temperatures are 100 F to 102 F, core temperature is suggested as "optimal" for the maximum efficiency burning rate of muscle glycogen stores. When perspiration first appears on the brow, core body temperature is 102 F.

7. Individual Fitness and Acclimatization Hindered by: Lack of acclimatization or fitness training effects by up to 50 percent. The same fit athlete finishing the event in 8 days would otherwise finish the event in only 12 days in an un-fit, un-acclimatized state. The fit, acclimatized athlete has higher tissue buffering and enzymatic capacities for efficient endurance energy production. The fit athlete also requires 50 percent of the electrolyte stores of an un-fit, un-acclimatized athlete.

8. Age, Gender, Body Mass Index. Hindered by: Genetic capacity and hormone mechanics (related to gender) favor the leanest muscle-mass to body fat ratio specimen. Age is another cause for variable responses to the rate of carbohydrate intake upon its oxidation rate in the working muscles. Youth is usually an advantage here.

No wonder race organizers "guesstimate" an 8 to 12 day finish time - anything can happen to the body when an athlete negotiates a 37,000-45,000 caloric expense for generating movement of a 120 or 150 pound mass across 300 miles of thick jungle overgrowth.

REFERENCES [1]-Coggan A.R., Coyle E.F., Effect of carbohydrate Feedings During High Intensity Exercise, Journal of Applied Physiology, 1988; 65:1703-1709. [2]-American Dietetic Association Website http://www.eatright.org/ [3]-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. [4]-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.

[*Dr. Bill Misner, Ph.D., Director of Research & Product Development, E-CAPS INC. & HAMMER NUTRITION LTD. 1-800-336-1977; www.hammergel.com; www.e-caps.com]

REPRINTED BY PERMISSION © 2000