Weight management for endurance athletes is different from weight management for nonathletes in several ways. First of all the goal is different. The nonathlete's goals in losing weight are typically to look better and be healthier. Runners and other endurance athletes like to look good and be healthy too, but they also care about performance, and an athlete's optimal racing weight is not the same as his or her healthy weight range. Most often, the body weight at which an athlete performs best falls at the lower end of his or her healthy weight range.
Endurance athletes must also be a little more careful than nonathletes about how they shed excess body fat. Nonathletes may, if they so choose, maintain fairly large daily energy (i.e. calorie) deficits in order to lose weight quickly. But a cyclist who does this will perform poorly in training and recover slowly after workouts. Low-carb diets are also a viable option for nonathletes. But a triathlete who goes on a low-carb diet robs him- or herself of the most precious fuel for endurance performance. Studies have shown that the more carbohydrates an athlete eats, the harder that athlete can train.
More: The Runner's Diet
Another difference between athletic and nonathletic weight management is subtler and more often overlooked. This one has to do with weight fluctuations over the course of the year. Studies involving individuals who have lost significant amounts of weight have demonstrated that any subsequent drift in weight is risky. Those who gain back a little weight are likely to gain it all back eventually. The men and women who are most successful in maintaining significant weight loss are exceptionally consistent in their diet and exercise habits throughout the year and therefore maintain a very steady weight.
For endurance athletes, this is unrealistic. Training and racing occur in cycles. To do your best in races you have to build your training to a peak level that is sustainable only for a short period of time. After a big race you must then take it easy for a while before you start another gradual build-up.
Even if you're already quite lean at the start of a training cycle, you are likely to lose a little weight as your training approaches the peak level, when you attain your ideal racing weight a few weeks before your biggest race. Peak fitness and optimal racing weight go hand in hand. Consequently, you can't expect to maintain your racing weight year-round any more than you can expect to hold peak fitness from January to December.
The greatest endurance athletes in the world gain a little weight—and we're not talking about muscle—during the off-season period between training cycles. Two-time Ironman world champion Chris McCormack weighs as little as 171 pounds when he toes the starting line in Kona. By the end of the winter break (which is actually a summer break in McCormack's native Australia) that follows this season-ending event, his weight is usually closer to 185 pounds.