Effects of a High vs Moderate Volume of Aerobic Exercise on Adiposity Outcomes in Postmenopausal Women: A Randomized Clinical Trial.

IMPORTANCE: Body fat increases postmenopausal breast cancer risk. Physical activity may decrease risk through adiposity changes, but the optimal dose of activity is unknown.

OBJECTIVE: To compare the effects of 300 vs 150 min/wk of moderate to vigorous aerobic exercise on body fat in postmenopausal women.

DESIGN, SETTING, AND PARTICIPANTS: The Breast Cancer and Exercise Trial in Alberta was a 12-month, 2-armed, 2-center randomized dose-comparison trial conducted from June 2010 through June 2013. Participants were 400 inactive postmenopausal women with body mass index 22 to 40, disease-free, nonsmokers, and nonusers of exogenous hormones.

INTERVENTIONS: Five d/wk of aerobic exercise (3 d/wk supervised, 2 d/wk unsupervised) for 30 min/session (moderate-volume) or 60 min/session (high volume) achieving 65% to 75% of heart rate reserve for at least 50% of each session. Participants were asked not to change usual diet.

MAIN OUTCOMES AND MEASURES: Total body fat, measured from dual energy x-ray absorptiometry scans, was the primary outcome. Other measures included subcutaneous and intra-abdominal fat from computed tomography scans, weight, and waist and hip circumferences.

RESULTS: Of 400 women, 384 provided baseline and follow-up adiposity measurements. Median (interquartile range) adherence at full prescription for the high- and moderate-volume groups was 254 (166-290) and 137 (111-150) min/wk, respectively. Mean reductions in total fat were significantly larger in the high- vs moderate-volume group (least-squares mean difference, -1.0% [95% CI, -1.6% to -0.4%], P = .002). Subcutaneous abdominal fat and waist to hip ratio decreased significantly more in the high-volume group (least-squares mean difference, -10.8 [95% CI, -19.5 to -2.2] cm², P = .01, and -0.01 [95% CI, -0.02 to 0.00], P = .04, respectively). Changes in weight and intra-abdominal fat were not significantly different between groups (least-squares mean difference, -0.7 [95% CI, -1.6 to 0.2] kg, P = .11, and -1.5 [95% CI, -5.9 to 2.9] cm², P = .50, respectively). Some dose-response effects were stronger for obese women.

CONCLUSIONS AND RELEVANCE: In previously inactive postmenopausal women, a 1-year prescription of moderate to vigorous exercise for 300 min/wk was superior to 150 min/wk for reducing total fat and other adiposity measures, especially in obese women. These results suggest additional benefit of higher-volume aerobic exercise for adiposity outcomes and possibly a lower risk of postmenopausal breast cancer.

TRIAL REGISTRATION: clinicaltrials.gov: NCT01435005.