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Get fat, live longer???

Friday, July 31, 2009 Posted by Travis Saunders


If you follow obesity research with even a passing interest, there is a good chance that you have seen the now infamous editorial by Margaret Wente which was published in the Globe and Mail earlier this week.  In her editorial, Ms Wente describes a recent study in Obesity which examined the links between body mass index and mortality in a group of 12,000 Canadians.  Ms Wente makes several arguments - many of which are completely refuted by the available evidence - and I think that both her editorial and the study itself deserve some further analysis.

The study, which was led by Statistics Canada researcher Heather Orpana, reported that individuals who were overweight in 1994 were at significantly decreased risk of mortality over the 12-year follow-up when compared to individuals in the normal weight category.  Now for several reasons that I will get to in a moment, that isn't actually all that shocking. But I can see why it would seem pretty earth-shattering to people unfamiliar with the field of obesity research, which apparently includes Ms Wente.  You see, Ms Wente takes these findings to suggest that people should "Get fat, live longer".  Now of course Orpana and colleagues did not examine whether gaining weight makes people live longer - they only looked at the associations between baseline weight and mortality.  But that's not the biggest detail that Ms Wente overlooked.  In fact, she says that 

“being obese was associated with a 12-per-cent lower risk of dying”

But you see, the study didn't show that at all.  In fact, the Globe published a letter to the editor from the study authors on Wednesday correcting Ms Wente, saying that

"None of the analyses reported in our paper...showed that obesity (a body mass index ranging between 30 and 35) was associated with lower mortality."

Ouch.  

Let's get back to Ms Wente's argument that people should gain weight to live longer.  To support her point, she cites an Annals of Internal Medicine review paper from 1993 which reported that individuals who gained a modest amount of weight as they aged had the lowest risk of mortality, while those who lost a large amount of weight had a dramatic increase in mortality.  But the majority of studies in that review article failed to control for "unintentional" weight loss due to underlying cancer or other serious diseases (some did control for heart disease, however).  This means that they lumped unintentional weight loss due to disease with "intentional" weight loss due to lifestyle changes.  Unintentional weight loss is almost always bad, and may have been driving the relationship between weight loss and mortality in the Annals paper.  When we look instead at more recent research focusing on "intentional" weight loss in overweight and obese adults, we see an overwhelming majority of studies which report that weight loss actually reduces the risk of mortality, just as we would expect.  For example, a study in the American Journal of Epidemiology reports that "[in overweight women] intentional weight loss of any amount was associated with a 20% reduction in all-cause mortality". Why Ms Wente chose to avoid the wealth of current research in favour of a review article with such a major limitation I am not sure. If I had to guess, I would say it was because the majority of current research completely refutes her argument.

Now let's return to the current study in Obesity, because it is a genuinely interesting paper.  As I mentioned earlier, the study assessed the association between body mass index and mortality in a sample of 12,000 Canadians.  I've been chatting with a lot of people about this paper the past few days so I'd like to outline what I think we can learn from it.

The main point I would take from this paper is that body weight is associated with health risk, and as usual, it was a J shaped curve with increased risk observed at both very high and very low BMI's.  So as usual, you want to avoid being significantly over or underweight.  However, the reason that this study is so interesting is the nadir of the curve fell in the "overweight" range, rather than the "normal" range.  But when seen in the context of other research, that finding isn't all that surprising.  For example, Flegal and colleagues reported similar results in an American sample in 2005, as have some (but not all) others.  In fact, I don't think anyone knows for certain what the "ideal" BMI is, and it is almost certainly different for people of different genders and ethnic backgrounds (for example Asian individuals often begin to experience metabolic complications at much lower BMI's than Caucasians). The current BMI guidelines may be a bit conservative for Caucasians, but public health guidelines should err on the conservative side, especially in a country with a wide range of ethnic backgrounds like Canada.

It is also important to keep in mind that where you store body fat is probably more important than how much body fat you have. For example, body fat stored in the legs has consistently been shown to protect against metabolic risk in longitudinal studies. In contrast, abdominal fat, and in particular visceral fat, is independently associated with increased risk of morbidity and mortality. People who have high BMI’s tend to have high amounts of visceral fat, which is probably responsible for much of the relationship between BMI and health risk. However, some people with high BMI’s store body fat mainly in their lower body (the “pear” body shape), and these individuals often have very little metabolic risk at all. Similarly, although less common, some individuals with a high BMI are merely very muscular (these people also have low health risk).

We also know that when people exercise, they preferentially reduce the visceral fat that is responsible for much of the obesity-related health risk.  Even when there is little or no change in body weight, chronic exercise results in decreased visceral fat, and decreased health risk.  This is likely one reason why research has consistently shown that it is better to be overweight and physically active, rather than lean and inactive.

This means that if you are exercising regularly, even if you are not losing weight, you are still dramatically reducing your risk of diabetes, heart disease, and several types of cancer.  Too often people quit their exercise program because they feel they are not losing enough weight, or not losing weight fast enough, and they don't realize all of the benefits that come from exercise irrespective of changes in body weight.  So I hope this study helps people realize that they should focus on what matters - living a healthy lifestyle - and stop focusing so much on their body weight.

So what's the take-home message from this lengthy post (aside from ignoring health advice from Margaret Wente)?  Body weight affects your health, but not as much as diet and exercise.  So focus on those healthy behaviors, and you'll be moving towards a longer, healthier life.

Hat tips to Alex Green and Alex Hutchinson for sending me the Globe article and/or related links.  As always, to receive all of the latest obesity news and research via email, you can sign-up here.

Travis

Orpana, H., Berthelot, J., Kaplan, M., Feeny, D., McFarland, B., & Ross, N. (2009). BMI and Mortality: Results From a National Longitudinal Study of Canadian Adults Obesity DOI: 10.1038/oby.2009.191

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11 Response to "Get fat, live longer???"

  1. Charlotte Said,

    I like the redesign - much easier on the eye.

    Thanks for the write-up - the 'overweight people live longer' articles crop up in the papers pretty regularly, and it's nice to get a more sensible look at the research.

    Posted on July 31, 2009 at 5:02 PM

     
  2. darya Said,

    Well done!!! Marked this to share with my readers. And the site is soooo much easier to read. Thanks!!

    Posted on July 31, 2009 at 6:11 PM

     
  3. Travis Saunders, MSc Said,

    @ Charlotte & Darya,

    Glad to hear that you enjoyed the article, as well as the new layout! Peter's hard work on the layout has really paid off.

    Travis

    Posted on July 31, 2009 at 8:13 PM

     
  4. Anonymous Said,

    On the other hand....

    The Figure Flaw Paradox - Does it Really Matter How Your Body Measures Up?

    http://junkfoodscience.blogspot.com/2009/06/figure-flaw-paradox-does-it-really.html

    Posted on July 31, 2009 at 11:59 PM

     
  5. Arya M. Sharma, MD Said,

    Well said! There simply is no simple way to look at this issue (sure you've seen my own extensive discussions of this topic).

    BTW regarding body-image and self esteem check out the posts on http://dr-eyecandy.blogspot.com/

    Keep writing!

    a

    Posted on August 1, 2009 at 2:07 AM

     
  6. Travis Saunders, MSc Said,

    @ Anonymous,

    Thanks for the link, I'll be sure to check it out!

    @ Dr Sharma,

    Thanks for the kind words! Your own writings on this topic have thoroughly influenced the way I think about BMI. Thanks as well for the link.

    Posted on August 1, 2009 at 11:06 AM

     
  7. Travis Saunders, MSc Said,

    Peter and I have been discussing the Junkfood Science website quite a bit this morning, and I think we'll come back to it in the future. In the meantime, here is a very good analysis of Junkfood Science from the Denialism Blog on ScienceBlogs.com.

    Posted on August 1, 2009 at 2:49 PM

     
  8. Anonymous Said,

    I checked out what was said about junkfoodscience blog from your link, and I don't think he makes his case. Perhaps he is correct in asserting that fat people are being kept alive longer due to treatment for hypertension, high blood sugar, etc., but I don't think the research demonstrates that at all. In fact, many overweight people are not on various meds, or stop taking them. Also, Ms. Szwarc cites studies that account for lower BMIs being due to illness, and still the thinnest die earlier.

    Nor does the blogger addresss many of the other points Ms. Szwarc makes concerning the hazards and failures of bariatric surgery.

    He is also completely wrong when he states that she is anti-exercise, when in fact she is very pro-exercise and pro-fitness for health.

    I would also direct you to Dr. Nortin Hadler, MD, and his articles at abcnews.com and his books, Worried Sick and The Last Well Person.

    Much of what passes for fact today is often myth or the result of prejudice. It is easier to say, "You're unhealthy." than to say, "I don't like the way you look."

    Posted on August 1, 2009 at 11:28 PM

     
  9. Anonymous Said,

    I would like to chime in in defense of Sandy Swzarc's blog. Yes sometimes she gets a little carried away and she is very libertarian in her thinking. But her analyses of published articles are often extremely astute and interesting, and she has a gift for pointing out internal flaws and contradictions. I feel her work is very valuable, and of course a reader can always go read the article for himself/herself and see if what she says is accurate. She has long detailed and carefully thought out analyses. The attack on her on the denialism blog is excessive and not well-motivated. She is not just some purveyor of nonsense, far from it, and she should not be pigeonholed into a blanket "denialist" category. What she says should be taken seriously.

    Posted on September 2, 2009 at 2:20 AM

     
  10. justjuliebean Said,

    I think she's a hack. However, I may be biased, I've never met a libertarian that I've liked.

    Posted on November 10, 2009 at 2:49 AM

     
  11. Proud FA Said,

    Gluttony is good for health care profits in the short term but in the long term fatlings die sooner so they cost health care less than normal people.

    We at Bigger Fatter Blog aka the new fat acceptance would like to issue the following statement from our fat acceptance blog.

    This is the next phase in fat acceptance. The days of justifying our fatness by lying and saying we have a mysterious genetic or metabolic disorder are over. We now freely admit to and embrace what the fat haters would call gluttony. We fatlings are no longer apologists for our size nor our greedy gluttony. We are fat because we eat huge amounts of food and we like it. If you don't like it get used to it because fat people are now the overwhelming majority

    Posted on February 18, 2010 at 3:09 AM

     

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We are PhD students in the School of Kinesiology and Health Studies at Queen's University in Kingston, Ontario. Our research focuses on the relationships between obesity, physical activity, and health risk. This blog is our attempt to consider the many "cures" for obesity that we read about on a daily basis. Enjoy.

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The opinions expressed here belong only to Peter and Travis and do not reflect the views of any organization. Any medical discussion on this page is intended to be of a general nature only. This page is not designed to give specific medical advice. If you have a medical problem you should consult your own physician for advice specific to your own situation.

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