A new study shows women need 60 minutes of moderate exercise a day to prevent weight gain as they age if they consume a normal diet.

The findings suggest women need more exercise than the current federal guidelines of 150 minutes a week, or 30 minutes five days a week, of moderate-to-intense activity.

The study is being published in the March 24/31 edition of the Journal of the American Medical Association.

"I don't want people to throw up their hands and say 'I can't do it','' said I. Min Lee, the study's lead researcher and a doctor and associate professor at Harvard Medical School and Brigham and Women's Hospital in Boston.

Women at a normal weight who consume a normal diet can beat middle-age weight gain by working out intensely for 30 minutes a day, whether by running, cycling, swimming laps or working out at a gym. Weight gain can also be prevented with 60 minutes of moderate activity, such as walking, a leisurely¹ bike ride or playing catch.

The federal guidelines of 150 minutes a week of moderate-to-intense exercise are designed to prevent disease and obtain other health benefits. However, a 2002 report by the Institute of Medicine suggested 60 minutes a day, or 420 minutes a week, are needed to prevent weight gain.

Dr. Lee said because the basis of IOM's findings have been questioned, she and other researchers decided² to look at the issue within the group of women participating in the federal Women's Health Study. She also said the goal was to look at women who weren't dieting and were consuming a normal diet to see what impact physical activity has on weight.

The study looked at 34,079 healthy U.S. women who consumed a usual diet from 1992 to 2007. The women were all age 45 or older at the start, with an average age of 54. They were given a questionnaire about the amount of exercise or activity they engaged in per week at the start of the study and then at three-year intervals³. Their activity was tracked for an average of 13 years while weight changes were tracked over a three-year period.

Overall, women gained an average of 5.7 pounds in the study. However, those who were normal weight, with a body-mass index of less than 25, maintained their weight if they exercised for 60 minutes a day. Women who exercised less generally gained weight. Dr. Lee said for overweight or obese⁴ women, 60 minutes of exercise a day wasn't enough to maintain weight, suggesting calories need to be cut.

一项新的研究显示，随着女性年龄的增长，在正常饮食的情况下，她们需要每天进行60分钟中等强度的运动，才能避免体重增加。

研究结果显示，女性需要的运动量要大于目前联邦指南建议的每周150分钟中等强度至高强度运动（相当于每周锻炼五天，每天30分钟）。

该研究报告发表在3月24日-31日的《美国医学会期刊》上。 该研究首席研究员、哈佛医学院和波士顿布里格姆妇女医院医生兼副教授I. Min Lee说，我不希望人们举手投降说，“我做不到”。

体重和饮食正常的女性可以通过每天进行30分钟的高强度运动──可以是跑步、骑车、游泳或在健身房中锻炼，避免中年时体重增加。每天进行60分钟中等强度的运动──比如走路、休闲性的骑车或接传球游戏──也可以防止体重增加。

联邦指南建议的每周150分钟中等强度至高强度运动是为了避免患病并获得其他健康益处。不过，美国医学研究所2002年公布的一份报告中建议，为避免体重增加，女性需要每天运动60分钟（也就是每周运动420分钟）。

该研究对1992年至2007年间饮食正常的34,079 名健康美国女性进行了研究。研究开始的时候，这些女性年龄都在45岁及以上，平均年龄为54岁。研究开始的时候，她们收到一份有关每周运动量的调查表，之后每三年进行一次问卷调查。研究人员对她们的运动量进行了平均13年的跟踪，而对体重变化的跟踪每三年进行一次。

Lee说，由于美国医学研究所研究结果的基础受到了质疑，她和其他研究人员决定在参与了“联邦女性健康研究项目”的女性人群中考察这个问题。她还说，目的是对没有节食、饮食正常的女性进行研究，考察体育运动对体重会造成怎样的影响。 总体来讲，研究期间这些女性的体重平均增加了5.7磅。不过，那些体重正常、体重指数(BMI)不到25的女性，如果每天锻炼60分钟，得以保持体重。运动量较少的女性体重往往会增加。Lee说，对体重超重或肥胖的女性来说，每天锻炼60分钟是不足以保持体重的，她建议要减少热量的摄入。