The 150 minutes a week of moderate-intensityphysical activity, which can be achieved by 30 minutes a day, five days a week,and which is recommended by the federal government, while clearlysufficient based on data from many studies to lower the risk of developingchronic diseases, is insufficient for weight-gain prevention, withoutrestricting caloric intake. Among women who are already overweight or obese,physical activity — at least, at levels carried out by participants inthis study — is not related to weight change, emphasizing the importanceof controlling caloric intake for weight maintenance in this group.“These findings shouldn’t obscure the fact that forhealth, any physical activity is good, and more is better,” Lee emphasizes. “Itis important to remember that weight is only one aspect of health. Many studieshave shown that being physically active for even 30 minutes a day, five days aweek, significantly reduces the risk of developing many chronic diseases, suchas cardiovascular disease, some cancers, and type 2 diabetes.”This study was funded by the National Institutes of Health. If a middle-aged or olderwoman with a normal body mass index wants to maintain her weight over anextended period, she must engage in the equivalent of 60 minutes per day ofphysical activity at a moderate intensity, according to new findings by Harvard researchers at Brigham and Women’s Hospital (BWH).“There is plenty of research on treating overweight and obesity — that is,looking at strategies for weight loss among overweight or obese persons, butvery little research on preventing weight gain in the first place. Mostoverweight and obese persons who lose weight do not successfully maintain theirweight loss over time, and so, from a public health perspective, preventingthat initial weight gain is important,” said I-Min Lee, an associateprofessor of epidemiologyat Harvard School of Public Health (HSPH), epidemiologist in the Division of Preventive Medicine at BWH, and associate professorof medicine at Harvard Medical School. The findings are published inthe latest issue of the Journal of the American Medical Association. Lee and colleagues analyzed data reported from more than 34,000 healthy U.S.women in the Women’s Health Study over 13 years to examine the relationshipbetween the level of daily physical activity and weight change over time. Womenin the study reported their leisure-time physical activities every two to threeyears. Each time that physical activity was assessed, women were divided intothree groups, according to the amount of time they spent engaged in physicalactivity.The most active group of women spent the equivalent of 420 minutes a week(60 minutes a day) or more engaged in moderate-intensity physical activity.The second group engaged in the equivalent of at least 150 but less than420 minutes a week of moderate-intensity physical activity, and the leastactive group engaged in the equivalent of less than 150 minutes a week ofmoderate-intensity physical activity. An example of a moderate-intensityphysical activity is brisk walking.These three levels of physical activity were chosen based on the 2008 federalguidelines for physical activity, which recommended at least 150 minutes a weekof moderate-intensity physical activity for health, and a 2002 Institute ofMedicine report on recommended dietary intakes, which suggested that 60 minutesa day of moderate-intensity physical activity was needed to prevent beingoverweight, although the scientific basis for this level of activity has beenquestioned.Over the duration of the 13-year study, the average weight of participantsincreased by 6 pounds, which is a rate of weight gain similar to that ofcomparably aged women in the general population. Compared with the most activewomen, both the group physically active for 150 to less than 420 minutes a week,and the group physically active for less than 150 minutes a week gainedsignificantly more weight than the most active group. The two less-activegroups also were significantly more likely to gain at least 5 pounds, comparedwith the most-active group.Researchers discovered that the findings differed significantly, according towomen’s body mass index (BMI). Physical activity was associated with lessweight gain only among women with anormal BMI, which is less than 25. An average U.S. woman who is 5 feet, 5inches tall must weigh less than 150 pounds to have a normal BMI. Among heavierwomen, physical activity — at least, within the levels that study participantsundertook — was not related to less weight gain.In this study, researchers were able to identify a group of “successful weightmaintainers.” These were women who started with a normal BMI and managed tomaintain their weight, gaining less than 5 pounds at each weight assessment,throughout the study. These women, 13 percent of participants, consistentlyengaged in physical activity that was the equivalent of 60 minutes a day ofmoderate-intensity physical activity.Researchers concluded that:Among middle-aged and older women consuming ausual diet with no calorie restriction, moderate-intensity physicalactivity for 60 minutes a day is needed to maintain normal BMI and preventweight gain over time.