Claire, a high school track athlete, is careful about what she eats. Competing in the 5k, she feels that the leaner she is, the faster she will run. She avoids bread and other starchy foods, and hardly ever allows herself to eat the cookies and ice cream she enjoys. She is 8 pounds lighter than she was the previous season, but is puzzled and disappointed by the lack of improvement in her running times.
For many athletes, body composition is a major concern. After all, carrying extra body fat can make the body less efficient as it moves through space. A larger body also requires more fuel to move than a smaller one, and extra body fat can make it more difficult to cool the active body.
But unrecognized by many athletes is the potential cost of weight loss. Cutting calories to lose weight deprives the body of fuel needed to perform optimally, a situation exacerbated by over-restricting carbohydrates, an important energy source for active muscles.
Athletes who restrict calories are focused on losing fat, but in reality that dip on the scale comes from a variety of sources. Carbohydrate stored in liver and muscle as glycogen for quick energy is rapidly diminished, and some loss of muscle tissue also occurs. This is magnified when the gap between energy needs and energy intake is large. Each pound of glycogen and muscle protein is bound to 3 pounds of water, so the scale may dip substantially with minimal loss of body fat. Also of concern, inadequate energy intake slows down the rate of bone growth in teens. When continued for a period of time, energy deficits can lead to dehydration, an increased risk of injury, weakened bones, and a decline in performance.
How to avoid the negative consequences of dieting
An athlete who is clearly overweight (BMI >85th percentile for teens and >25 kg/m2 for adults) might benefit from weight loss when done correctly (note that BMI does not accurately assess overweight in highly muscular individuals). However, lean athletes hoping to become leaner run the risk of causing more harm than good.
Here are some tips for avoiding the negative consequences of dieting:
- Know how many calories your body uses for normal metabolic needs and the energy cost of your workouts. Do not reduce calories by more than 500 daily (large guys can reduce up to 1000 calories daily).
- Fuel your workout, not your down time. Include a small meal or snack within 3 hours of starting exercise and within 1 hour of finishing.
- Include adequate carbohydrate foods including minimally processed grains (whole grain cereal, bread, brown rice), fruits and vegetables.
- Include adequate protein from lean sources such as chicken, turkey, eggs, lean cuts of beef or port, beans, and low fat dairy foods.
- When possible, avoid weight loss during the competitive season.