Exercise and healthy eating reduce body fat and preserve muscle in adults better than diet alone, according to a study funded and conducted by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health (NIH).  

NIDDK senior investigator Kevin Hall, PhD, analyzed the individual effects of daily strenuous exercise and a restricted diet by examining data from 11 participants from the reality television program "The Biggest Loser." Researchers measured body fat, total energy expenditure, and resting metabolic rate 3 times: at the start of the program, at week 6, and at week 30, which was at least 17 weeks after participants returned home. Participation in the program led to an average weight loss of 128 pounds, with about 82% of that coming from body fat, and the rest from lean tissue.

Hall used a mathematical computer model of human metabolism to calculate the diet and exercise changes underlying the observed body weight loss. Because the TV program was not designed to directly address how the exercise and diet interventions each contributed to the weight loss, the computer model simulated the results of diet alone and exercise alone to estimate their relative contributions.

At the competition's end, diet alone was calculated to be responsible for more weight loss than exercise, with 65% of the weight loss consisting of body fat and 35% consisting of lean mass such as muscle. In contrast, the model calculated that exercise alone resulted in participants losing only fat, and no muscle. The simulation of exercise alone also estimated a small increase in lean mass despite overall weight loss.

The simulations also suggest that the participants could sustain their weight loss and avoid weight regain by adopting more moderate lifestyle changes, such as 20 minutes of daily vigorous exercise and a 20% calorie restriction, than those demonstrated on the television program.