Sports nutrition advice for weight-conscious individuals in half-marathon training, marathon training, or triathlon training

Every endurance athlete knows that body weight (as well as body composition, or body-fat percentage) affects endurance performance. It pays to be light and lean. Consequently, the average endurance athlete struggles to attain his or her optimal body weight just as much as the average non-athlete struggles to attain a healthy weight.

Non-athletes commonly diet, or reduce their food intake, to lose weight. For those in half-marathon training, marathon training, or triathlon training, however, it’s often not so simple because endurance exercise places high energy demands on the body and reducing food intake can deprive the muscles of the energy they need for optimal performance and subsequent muscle recovery.

Short-Term Slim-Down Study

There is some new evidence, however, that endurance athletes can lose weight through dieting without sabotaging their training if they take a careful approach. In a 2009 study published in the Journal of Strength and Conditioning Research, scientists from George Washington University placed 10 competitive cyclists on a reduced-calorie diet (up to 40 percent) for three weeks and modified their training to include morning workouts in a fasted state (no breakfast). All of the subjects submitted to a variety of tests, including body composition and resting metabolic rate measurements and a performance test—both before and after the intervention.

The diet yielded no changes in fat burning during exercise, maximum power output on the bike, or power at VO2max. However, the cyclists’ rating of perceived exertion during two hours of submaximal exercise decreased (meaning the same effort felt easier) and their body composition and power-to-weight ratio improved significantly.

This study shows that endurance athletes can shed excess body fat relatively quickly and maintain their performance while on a fairly restrictive short-term diet. But there was no control group, so we can’t rule out the possibility that the diet prevented these cyclists from improving their power output and power at VO2max over the three-week study period.

The Diet’s Downside

I actually spoke with one of the participants in the study, who told me that the diet was not easy. He struggled with all-day hunger throughout it and went straight back to his normal eating habits as soon as the intervention was completed. So while the diet was effective in the short-term, it was not sustainable in the long-term. Undoubtedly, his performance and that of the other subjects would have begun to suffer if they had kept up caloric deficits of as much as 40 percent much longer than three weeks.

Other studies, involving athletes in weight-class sports such as rowing and wrestling, have shown that the severe dieting methods engaged in during the final weeks and days before competition do in fact sabotage performance. So there is clearly a limit to what we can get away with.

Developing a Smart Endurance Sports Nutrition Plan for Weight Loss

Based on the totality of available research, I believe that those in half-marathon training, marathon training, triathlon training, or any other type of endurance-sport training should generally try to lose excess body fat gradually through sustainable improvements in diet quality (get specific tips on how to do this in my earlier blog Weight Loss for Endurance Athletes) and sensible increases in training load whose primary intent is to boost fitness. Occasional efforts to lose weight more quickly are OK, but avoid cutting calories so much that your training suffers, keep these efforts relatively brief (2 to 4 weeks), and use them early in the training process, not close to races.