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] cm(2), 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] cm(2), 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.