The majority of randomized, controlled trials (RCTs) show only modest
weight loss with exercise intervention alone, and slight increases in weight
loss when exercise intervention is added to dietary restriction. In most
RCTs, the energy deficit produced by the prescribed exercise is far smaller
than that usually produced by dietary restriction. In prospective studies that
prescribed high levels of exercise, enrolled individuals achieved substantially
greater weight loss—comparable to that obtained after similar energy deficits
were produced by caloric restriction. High levels of exercise might, however,
be difficult for overweight or obese adults to achieve and sustain. RCTs
examining exercise and its effect on weight-loss maintenance demonstrated
mixed results; however, weight maintenance interventions were usually
of limited duration and long-term adherence to exercise was problematic.
Epidemiologic, cross-sectional, and prospective correlation studies suggest
an essential role for physical activity in weight-loss maintenance, and post
hoc analysis of prospective trials shows a clear dose–response relationship
between physical activity and weight maintenance. This article reviews the
role of physical activity in producing and maintaining weight loss. We focus
on prospective, RCTs lasting at least 4 months; however, other prospective
trials, meta-analyses and large systematic reviews are included. Limitations
in the current body of literature are discussed.