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    Losing weight after being obese increases life span in rats

    Posted by .(JavaScript must be enabled to view this email address)
    Thursday, May 19, 2005 8:31 am Email this article
    Rats that were once obese, but who were put on a diet as adults to lose weight, lived longer than rats that remained obese their entire life, and lived as long as rats that were never obese according to a new study. Diet composition did not affect life span

    Diet composition had no effect on life span.

    Rats that were fed a high-fat diet containing 45 percent of their calories as fat lived just as long as rats fed a low-fat diet containing on 19 percent of their calories as fat.

    Conclusion: Losing weight as an adult increases life span

    “Weight loss after the onset of obesity during adulthood leads to a substantial increase in longevity in rats,” the authors concluded.

    Diet started at 35-years-old in human years

    The rats were put on a diet at the age of 46-weeks, which I calculate to be the human equivalent of roughly 35-years-old.

    (I believe that the average life span of Sprague-Dawley rats used in this study is about 2 years, therefore, 10.5 months (46 weeks) is roughly the equivalent of 35-years-old for a human.)


    Some human studies have found similar results, although some studies have found that substantial weight loss after the age of 50 increases the risk of death.

    These studies which have found an increased risk of death in older people have suggested that perhaps older people should not be encouraged to lose weight. I disagree with this conclusion.

    I think the reason that substantial weight loss in older people is associated with an increased risk of death, is because it tends to be caused by an underlying disease or depression, and it is the disease or the depression which increases the risk of death, not the weight loss.

    Some studies try to distinguish between intentional and unintentional weight loss, but I believe these are far from perfect.

    I believe that an overwhelming majority of people would like to lose some weight, even if it is just a few pounds. Therefore, I believe that people who have unintentional weight loss due to an underlying disease or depression, may often take credit for losing weight, that is, say that it was intentional when it was not.

    This current study in rats, suggests that, if you are obese, losing weight, even as an adult, increases life span.


    Vasselli J, Weindruch R, Heymsfield S, Pi-Sunyer FX, Boozer CN, Yi N, Wang C, Pietrobelli A, Allison D. Intentional weight loss reduces mortality rate in a rodent model of dietary obesity. Obes Res. 2005 Apr, 13(4):693-702.


    David Allison
    Department of Biostatistics
    University of Alabama
    Ryals Public Health Building, Room 327
    1665 University Boulevard
    Birmingham, Alabama 35294-0022
    .(JavaScript must be enabled to view this email address)

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