Compared to women exercising half as much, postmenopausal women who exercised 300 minutes per week — nearly 45 minutes each day — were better at reducing total fat during a one-year clinical trial.

Postmenopausal women tend to put on extra weight, in particular abdominal fat, the authors of the study note, and this increases their risk of breast cancer. Research also suggests a link between postmenopausal abdominal fat and endometrial and colon cancers, metabolic syndrome, type 2 diabetes, and cardiovascular disease. Though many women find it easy to add pounds as they grow older, weight gain is not inevitable.

No-Cost Disease Prevention

A proper diet and exercise, as Mayo Clinic advises, will go a long way to counterbalancing the hormonal changes in an aging woman’s body that increase her likelihood of gaining weight around the abdomen. Commonly, abdominal fat is divided into two types: subcutaneous, which is visible flab, and visceral fat, which lies deep within and surrounds the heart, liver, and other organs. Physical activity is a no-cost way to rid the body of fat, including abdominal fat, and prevents disease. Yet, the benefit of exercising for a longer or shorter length of time needs further investigation, an editorial accompanying the new study proposes.

"Establishing the dose-response relationship of exercise is just like that for pharmacologic therapy — we need to know the minimum effective dose, whether there is a dose-response relationship, and when the point of diminishing returns might be reached," wrote Dr. Kerri Winters-Stone, Oregon Health and Science University.

To establish this important dose-response relationship, then, Dr. Christine M. Friedenreich, Alberta Health Services, and her colleagues examined the recommendation to exercise at moderate intensity for 150 minutes each week (or 75 minutes each week at vigorous intensity) in a clinical trial.

Enlisting the help of 400 inactive postmenopausal women, the researchers measured their body mass index (BMI) — they all fell within the range of normal (22) through obese (40) — and then split them into two separate exercise groups to compare the effects on body fat derived from 300 minutes of exercise per week versus 150 minutes per week. Most of the supervised and home-based exercise activities included elliptical trainer, walking, bicycling, and running. Importantly, the researchers requested the women, who ranged in age from 50 to 74, not change their usual diets.

Comparing the two groups after 12 months, the researchers discovered average reductions in total body fat were larger in the 300-minute group than the 150-minute group. The 300-minute group lost about one percent more body fat. Subcutaneous abdominal fat, as well as total abdominal fat, BMI, waist circumference, and waist-to-hip ratio also decreased more in the 300-minute group. For obese women (BMI greater than or equal to 30), the change in weight, BMI, waist and hip circumference, and subcutaneous abdominal fat were greater than for normal weight women.

"Our findings… provide a basis for encouraging postmenopausal women to exercise at least 300 minutes/week, longer than the minimum recommended for cancer prevention," the study concluded. If a little is good, more is better, this study suggests.

Source: Friedenreich CM, Neilson HK, O’Reilly R, et al. Effects of a High vs Moderate Volume of Aerobic Exercise on Adiposity Outcomes in Postmenopausal Women A Randomized Clinical Trial. JAMA Oncology. 2015.