Lawrence Berkeley National Laboratory

Background: Public health policies for preventing obesity need guidelines for active individuals who are at risk due to exercise recidivism. Methods: Changes in adiposity were compared to the running distances at baseline and follow-up in men and women whose reported exercise increased (N=4,632 and 1,953, respectively) or decreased (17,280 and 5,970, respectively) during 7.7 years of follow-up. Results: Per Delta km/wk, decreases in running distance caused over four-fold greater weight gain between 0-8 km/wk (slope+-SE, males: -0.068+ -0.005 kg/m2, females: -0.080+-0.01 kg/m2) than between 32-48 km/wk (-0.017+-0.002 and -0.010+-0.005 kg/m2, respectively). In contrast, increases in running distance produced the smallest weight losses between 0-8 km/wk and statistically significant weight loss only above 16 km/wk in males and 32 km/wk in females. Above 32 km/wk (30 kcal/kg) in men and 16 km/wk (15 kcal/kg) in women, weight loss from increasing exercise was equal to or greater than weight gained with decreasing exercise, otherwise weight gain exceeded weight loss. Substantial weight gain occurred in runners who quit running, which would be mostly retained with resumed activity. Conclusion: Public health recommendations should warn against the risks of irreversible weight gain with exercise cessation. Weight gained due to reductions in exercise below 30 kcal/kg in men and 15 kcal/kg in women may not be reversed by resuming prior activity. Current IOM guidelines (i.e., maintain total energy expenditure at 160 percent of basal) agree with the men s exercise threshold for symmetric weight change with changing exercise levels.