Purpose: Although increases and decreases in physical activity are known to cause weight loss and weight gain, respectively, it is not known whether the magnitudes of these changes in weight are equal. Unequal (asymmetric) weight changes could contribute to overall weight gain or loss among individuals with seasonal or irregular activity.
Methods: Changes in adiposity were compared with the running distances at baseline and follow-up in men and women whose reported exercise increased (N = 4632 and 1953, respectively) or decreased (17,280 and 5970, respectively) during 7.7 yr of follow-up.
Results: Per km·wk−1 decreases in running distance caused more than four times greater weight gain between 0 and 8 km·wk−1 (slope ± SE, males: −0.068 ± 0.005 kg·m−2; females: −0.080 ± 0.01 kg·m−2) than between 32 and 48 km·wk−1 (−0.017 ± 0.002 and −0.010 ± 0.005 kg·m−2, respectively). In contrast, increases in running distance produced the smallest weight losses between 0 and 8 km·wk−1 and statistically significant weight loss only above 16 km·wk−1. Above 32 km·wk−1 (30 kcal·kg−1) in men and 16 km·wk−1 (15 kcal·kg−1) in women, weight loss from increasing exercise was equal to or greater than weight gained from decreasing exercise; otherwise, weight gain exceeded weight loss.
Conclusion: Weight gained because of reductions in weekly exercise below 30 kcal·kg−1 in men and 15 kcal·kg−1 in women may not be reversed by resuming prior activity. Current IOM guidelines (i.e., maintain total energy expenditure at 160% of basal) agree with the men's exercise threshold for symmetric weight change with changing exercise levels. Asymmetric weight changes below this threshold may contribute to weight gain among less-active subjects.