Why even active people get fatter--the asymmetric effects ofincreasing and decreasing exercise

Background: Public health policies for preventing obesityneed guidelines for active individuals who are at risk due to exerciserecidivism. Methods: Changes in adiposity were compared to the runningdistances at baseline and follow-up in men and women whose reportedexercise increased (N=4,632 and 1,953, respectively) or decreased (17,280and 5,970, respectively) during 7.7 years of follow-up. Results: PerDelta km/wk, decreases in running distance caused over four-fold greaterweight 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 runningdistance produced the smallest weight losses between 0-8 km/wk andstatistically significant weight loss only above 16 km/wk in males and 32km/wk in females. Above 32 km/wk (30 kcal/kg) in men and 16 km/wk (15kcal/kg) in women, weight loss from increasing exercise was equal to orgreater than weight gained with decreasing exercise, otherwise weightgain exceeded weight loss. Substantial weight gain occurred in runnerswho quit running, which would be mostly retained with resumed activity.Conclusion: Public health recommendations should warn against the risksof irreversible weight gain with exercise cessation. Weight gained due toreductions in exercise below 30 kcal/kg in men and 15 kcal/kg in womenmay not be reversed by resuming prior activity. Current IOM guidelines(i.e., maintain total energy expenditure at 160 percent of basal) agreewith the men s exercise threshold for symmetric weight change withchanging exercise levels