How Many Calories Should You Eat While Training For A Triathlon?

Energy is expended in three ways: resting metabolic rate, physical activity, and the thermic effect of food, or digestion and metabolism. These factors, along with age, gender, training intensity and training duration, will all affect how many calories you should consume when training for a triathlon. The amounts of protein, carbohydrates and fat are equally as important as the total number of calories consumed.

Using Basal Metabolic Rate to Estimate Caloric Need

The resting or basal metabolic rate, or BMR, is the number of calories required by the body to maintain normal bodily functions, including respiration and circulation. There are several ways this may be calculated, and the Harris-Benedict Equation is commonly accepted as an accurate estimate. The equation is as follows:

Males: 66.473 + (13.7516 x kg) + (5.0033 x cm) - (6.755 x age)
Females: 655.0955 + (9.5634 x kg) + (1.8496 x cm) - (4.6756 x age)

To convert height and weight to metric measurements, divide weight in pounds by 2.2 and multiply height in inches by 2.54. Caloric need of the thermic effect of food is calculated by multiplying BMR by .1. Athletes participating in moderate-intensity training four or five days per week should multiply BMR by .75 and those intensely training for five or six days per week should multiply BMR by 1. Adding BMR, thermic effect of food and physical activity need will result in the total number of calories required to maintain body mass.

Carbohydrate Needs

Carbohydrates are used by the body as an immediate source of energy. In the blood, carbohydrate takes the form of glucose to be used by tissue cells. It is stored as glycogen in muscle and the liver, and these sources of energy are easily accessible by muscle cells and will be utilized first. Adequate carbohydrates should be consumed to provide the energy necessary for performance, as well as to replenish glycogen stores for subsequent workouts. Carbohydrate need is approximately 55 percent of total caloric need. A more specific number can be determined, with athletes requiring 7 to 8 g of carbohydrates per kilogram of body weight.

Protein Needs

Because of the duration of triathlon training and competition, higher levels of protein are often recommended when compared to non-athletes. Protein recommendations range from 10 to 35 percent of total caloric intake, and specific protein needs can also be calculated for individual athletes. At least 1.2 to 1.4 g of protein per kilogram of body weight should be consumed, and athletes participating in events that last several hours or days will likely require even greater amounts. In order for protein to be utilized for muscle building rather than metabolism, calories from protein should not be used to substitute those from carbohydrates.

Fat Needs

Fat is also an essential component of caloric need and it is recommended that athletes, as well as the general population, consume 10 to 35 percent of their calories from fat. The type of fat is also important, and saturated fat should constitute less than 10 percent of total fat with the rest being mono- or poly-unsaturated fats. Fats from your diet provide building blocks for cell membranes, hormones and some vitamins. Fat in foods also improves taste, texture and feelings of fullness, which can prevent overeating.

Nutritional Concerns of the Female Athlete

Low-energy intakes -- less than 1,800 to 2,000 calories per day -- may lead to a negative energy balance, meaning that the number of calories burned in the day is greater than the calories consumed. When this occurs, the body will begin to use fat and lean mass for energy with severe consequences. When body fat levels drop below 11 percent, it can lead to interruption or loss of menstrual cycle. Over long periods of time, irregular hormone cycles may have negative effects on bone density. Loss of lean mass can lead to decreases in muscular strength and endurance, causing decreased performance.

Constant calorie restriction may also lead to immune and endocrine system dysfunction, decreased nutrient intake and lowered resting metabolic rate. Researchers suggest that female athletes require a minimum of 30 calories per kilogram of fat free mass per day to prevent experiencing these negative effects of calorie restriction.