Essentials of Nutrition for Sports

Aerobic Endurance

Athletes’ Diet

Why High Carbohydrate?

Macronutrient Mix & Carbohydrate Key Points •^

Healthy diets are 60% carbohydrate, 25% to 30% fat, and 10% to 15% protein.

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Carbohydrate is the preferred fuel source for high-intensity exercise.

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Aerobic endurance athletes who exercise more than 10 hours per week benefit from a diet slightly higher in carbohydrate—typically up to 65% carbohydrate, 20% fat, and 15% protein.

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Even higher percentage carbohydrate diets may sometimes be best for aerobic endurance athletes.

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Aerobic endurance athletes may need 7 to 10 grams of carbohydrate per kilogram (3 to 4.5 grams per pound) of body weight per day to replace or top up glycogen stores.

Macronutrient Mix

The traditional high-performance aerobic-endurance diet consists

of 60% to 70% of calories as carbohydrate, 10% to 15% as protein and 15% to 25% as fat. Such a diet is typical of Tour-de-France riders. This is referred to as a high-carbohydrate diet.

Low-carbohydrate diets always have their followers. Current

examples include the South-Beach, the Atkins, and the 40–30–30 diet, in which carbohydrate makes up only 40% of total calories, and protein and fat make up the divided remainder.

Some have referred to these diets as “high fat.” In terms of

percentage fat content, such diets may be typical of the average US diet. However, they have a higher than average protein content.

Where Energy Comes From

Carbohydrate, protein, and fat can all be used to make energy.

Approximately 4 calories are produced from each gram of carbohydrate or protein metabolized; about 9 calories are produced from each gram of fat.

Where Energy Goes

The body needs energy to keep

the brain working, the heart

pumping, the kidneys filtering blood. The amount of energy needed for basal metabolic activities depends on the size of the individual—but let us say the average is about 1,000 calories per day.

The body also needs energy for physical activities—everything

from light activity including walking to the heavy activity of high-end endurance exercise. Heavy activity can use several thousand calories a day.

Food energy that the body does not need does not evaporate. The

body does not excrete calories. All calories ingested are either used to produce energy or stored as fat. Excess carbohydrate and protein are converted to fat and stored along with the excess dietary fat in the body’s fat deposits. (Importantly, the reverse does not happen except to a very minor degree—only a small portion of fat can be converted back to carbohydrate.)

How the Body Makes Energy

The body uses fat, carbohydrate, and protein to make energy via

partially different metabolic pathwa

ys. Protein is usually used in

building muscle or other functions; its contribution to energy production is relatively small and w

ill be ignored in this discussion.

At rest and at low levels of activity, relatively more fat is used

for energy production. As activity levels become more intense, more carbohydrate is used to make energy.

Nutrition for Sports, Essentials of 47