For middle-aged women who aren’t counting calories, how much exercise does it take to keep off extra weight? According to a new study published this week in the Journal of the American Medical Association, roughly an hour per day. Though current recommendations from the Department of Health and Human Services suggest that a weekly 150 minutes (or half hour five days per week) of moderate exercise—activities like hiking—is enough for weight maintenance, after up to 13 years of follow-up with more than 34,000 women in this latest study, researchers found that maintaining a healthy weight required more than double that amount of moderate physical activity. What’s more, for women who were already overweight, exercise on its own wasn’t enough to help them get back down to a normal range body mass index (BMI). Examining the impact of exercise alone, only women who were at a normal BMI at the study’s onset were able to maintain their healthy body weight—and they did it through routine, prolonged physical activity.
The study, conducted by a team of researchers from Harvard Medical School, Brigham and Women’s Hospital and the Massachusetts Veterans Epidemiology and Research Information Center, included 34,079 healthy women with a median age of 54.2 years. Study participants were asked to regularly complete health questionnaires, twice during the first year of the study and annually thereafter, reporting their weight and physical activity. Based on their responses, women were categorized into three different groups—those who exercised 150 minutes or fewer each week, those who worked out between 150 to 420 minutes per week, and those who exercised more than one hour per day each week. On average women in all three groups gained about 6 lbs. (2.6kg) over the course of the study. Some women who started with a normal range BMI (under 25 kg/m), were able to maintain a healthy weight across the study period—13.3% (or 4,540 of the more than 34,000 included in the study); in this group, the average amount of moderate-intensity exercise was roughly one hour per day.
The findings indicate that current government guidelines underestimate how much exercise older women need to keep off weight without also cutting back calories, the researchers conclude. And what’s more, they also emphasize the importance of prevention when it comes to weight gain—after all, as most people who have entered into the diet cycle can attest, once you gain weight, it’s very difficult to lose it, and keep it off. As they write, “[O]nce overweight, it may be too late because physical activity—at least, at levels carried out by study participants—was not associated with less weight gain.”