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An hour of daily exercise helped women stay trim–If they had normal BMIs

The views expressed are those of the author and are not necessarily those of Scientific American.


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hour exercise women age weightTaking the stairs, taking a hike, taking a yoga class, or any other moderate physical activity recently helped thousands of healthy women maintain their weight for 13 years without cutting calories, a new study reports. The only catch is that it only worked for women with a normal body mass index (BMI) who exercised for an hour daily.

The federal government, along with the American Heart Association and others, recommends getting 150 minutes of moderate physical activity a week (about 20 minutes a day), whereas the Institute of Medicine (IOM) has advocated for 450 minutes (about 60 minutes a day). According to the National Institutes of Health, the ranges of BMIs are:
•    Less than 18.5 is underweight;
•    18.5 to 24.9 is normal;
•    25 to 29.9 is overweight and
•    more than 30 is obese.

Between 1992 and 2007, researchers behind the new study checked in with 34,079 relatively healthy middle age and older women seven times to gather information on weight and physical activity levels. For women under the age of 65 and with BMIs below 25, exercise made a big difference. Those in that group who got less than 420 minutes of moderate activity each week "gained significantly more weight" than those who were able to squeeze in more than 60 minutes a day, reported the team, which was led by I-Min Lee, of the Division of Preventive Medicine at Brigham and Women’s Hospital at Harvard Medical School.

Unfortunately, for women who started the study either overweight or obese and who maintained average U.S. eating habits (didn’t trim their caloric intake), the amount of moderate activity did not seem to affect their statistical likelihood of losing weight.

The researchers concluded that this might indicate that, "once overweight, it may be too late" to rely on moderate activity alone to achieve a healthier BMI. The results were published online March 23 in JAMA, Journal of the American Medical Association.

Even though the federal recommendation for 150 minutes of physical activity each week is "clearly sufficient to lower the risks of chronic diseases," the researcher noted, it "is insufficient for weight gain prevention absent caloric restriction."

In the U.S., where one in three adults is considered obese, the sheer numbers "present a tremendous health care challenge in treatment and cost relating to the many adverse health conditions associated with excess body weight," the researchers noted. Even small weight gains, such as the average 2.6 kilograms that study participants put on over the course of the study, can make a cumulative impact on health—for both individuals and the overall disease burden—especially as "the majority of persons losing weight do not maintain their weight loss," the authors noted. So keeping the pounds off in the first place is, indeed, "preferable," as Lee and colleagues wrote.

Image courtesy of iStockphoto/diego_cervo





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  1. 1. AndrewJayPollack 7:38 pm 03/23/2010

    You lost me at BMI. Anyone who uses this bullshit measurement as anything other than scratch notepaper should be slapped.

    BMI is an over generalization of health based on an over generalized ratio of height and weight suitable only for people who have a slight build.

    Does this cause trouble? Damn right.

    In my case, I’m 5’9" tall and 215 pounds. According to the BMI, I am obese (possibly morbidly obese). Of course, not reflected in that stupid chart is that at 42 years old I’m a structural firefighter, work out strenuously at karate 2-3 times a week, and comfortably wear pants with a 34" waist, while a 48" jacket barely goes around my shoulders.

    The above would seem to indicate that I’m in reasonable shape for a guy my age, yes? Tell that to the 5 life insurance companies who didn’t want to insure me based on a phone conversation after checking their BMI charts. The sixth, however, sent someone to actually look at me and give me a sort of quick health check, and checked a box labeled "weightlifter" (I don’t lift weights) — then proceeded to put me in their lowest risk category.

    BMI is not just useless, it is dangerous and misleading.

    Link to this
  2. 2. candide 8:09 pm 03/23/2010

    There are lies, damned lies and statistics.
    BMI is an extremely oversimple and useless statistic.

    Link to this
  3. 3. AndrewJayPollack 8:15 pm 03/23/2010

    it’s worse that useless. It’s the kind of bullshit number that turns teenaged girls into anorexics or bullemics; it destroys body image in those without self confidence; and it gives an excuse for insurance companies an avenue for abuse.

    Link to this
  4. 4. billsmith 8:53 pm 03/23/2010

    BMI may not be an accurate estimator of visceral fat for some of the more muscular individuals out there.

    It is, however, still a simple and effective correlate for fat and poor health when you are making comparisons within a large group of people. Maybe when medical-grade 3D scanners become cheaper, we’ll have a better way of measuring fat.

    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2678136
    http://www.jstage.jst.go.jp/article/circj/73/10/73_1881/_article

    Link to this
  5. 5. AndrewJayPollack 9:00 pm 03/23/2010

    @Bill – even that isn’t actually accurate despite the old articles in its favor. For example, studies in the last couple of years have show that the amount of fat on a body is less valuable an indicator of risk than it’s distribution. For women, fat carried on the hips its actually fairly normal and not an indication of risk, while belly fat can be a serious risk indicator — and for men the opposite seems to be the case.

    BTW: No high tech gear is necessary for an accurate quick assessment of body fat amount and distribution. A doctor or nurse practitioner can make a very much more useful and accurate assessment in a matter of a few seconds — and can follow that with a quick oral history to result in actual medical advice that is pertinent to the individual.

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  6. 6. VictorBravo 9:55 am 03/24/2010

    Valid points on BMI’s misleading overuse. Muscle weighs more than fat. For a fit man, conducting aerobic exercise and significant weight training three or so days a week for up to 45 minutes per day, the BMI will indicate obesity. Nonsense. America’s self delusion with appearance to utterly destructive. Look at our mental health as a consequence ….

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  7. 7. sunnystrobe 3:23 pm 03/25/2010

    Sorry, Harvard this is yet another research study that wasted a lot of time and money !
    "Thousands of healthy women maintaining their weight for 13 years without cutting calories" ?
    WHICH calories, please?
    Is it the Empty Calories version, provided by ‘Frankenstein’ Fast Food Industries in the shape of denatured, condensed and downright dangerous Ersatz food? Of course any medical research is bound to fail if we are not told WHAT food their objects of research are being fed ! Obesity is an INDUSTRIAL disease, which cannot be tackled until governments stop pussyfooting around the fact that the BIG food conglomerates must be made accountable for the health problems they cause. But what if this study has been sponsored by one of them? Professor Colin Campbell’ s China Study casts light on this dilemma. For an species-specific diet concept that is NOT biased by big food industry see youthevity.com

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