How much exercise is needed to reduce body fat—a known breast cancer risk factor—in postmenopausal women? That’s the question researchers explored in a study published in JAMA Oncology (2015; doi:10.1001/jamaon col.2015.2239).
The scientists recruited 400 previously inactive women, aged 50–74, with BMIs of 22–40, to participate in either moderate- or high-volume exercise for a year. The women were told to follow their usual diet during that time. Exercise volume ramped up gradually during the first 12 weeks. Then participants were asked to exercise five times per week, for either 30 minutes per session (moderate volume) or 60 minutes per session (high volume). A further goal was to achieve 65%–75% of maximum heart rate for at least half of each session.
Adherence rates were 91% and 85% for the moderate-and high-volume groups, respectively, with 384 women finishing the study. Both groups fell short of their duration goals, exercising for an average of 88 and 128 minutes, respectively.
Although the women did not meet study requirements, they did see improvements. Perhaps not surprisingly, the high-volume group was more successful than the moderate-volume group at losing weight.
“During a 12-month period, inactive postmenopausal women with BMI of 22 to 40 prescribed 300 vs. 150 minutes per week of moderate to vigorous aerobic exercise experienced a significantly greater reduction in mean total body fat (by 1 kg or 1% body fat),” the authors observed. “Mean reductions in BMI, waist circumference, waist to hip ratio, subcutaneous abdominal fat, and total abdominal fat were also significantly greater in the group prescribed 300 minutes per week.”
Women with a BMI of 30 or higher seemed to improve the most.
“A probable association between physical activity and postmenopausal breast cancer risk is supported by more than 100 epidemiologic studies, with strong biologic rationale supporting fat loss as an important (though not the only) mediator of this association. Our findings . . . provide a basis for encouraging postmenopausal women to exercise at least 300 minutes per week, longer than the minimum recommended for cancer prevention,” the authors concluded.