Health
Habits
Food
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1 lb Fat
Last week the New York Times and many other reputable news sources reported on a Canadian study that claims people with a normal body mass index (BMI) had a slightly increased risk of dying over a 12-year period than those with a BMI in the overweight range (25-29).
The use of the phrase “overweight was protective” landed this article just a hair’s width from being labeled Summer Tomato’s B.S. of the week on Friday. An observational study cannot determine cause and effect, as implied by the word “protective.” This study does not prove that extra body weight protects against all cause mortality, and saying so is irresponsible.
Studies (and reporting) like this have instigated wide-spread confusion about health and body weight. First people are told they are too heavy and should lose weight for health, then in the same breath they are told a little extra weight might not be so bad.
What is the average person supposed to believe? How should we act?
If you want to understand the facts it important to know exactly what the data does and does not say. Indeed, some studies (including one on Japanese men reported in the same issue of Obesity) have reported lower or equal risk of mortality for people with an overweight BMI compared to people of normal BMI (18.5-24). However, this is not the whole story.
First, the alleged benefit of being overweight has only been found in older individuals and does not apply to healthy, young people. Second, although it appears in some cases that overall mortality may be reduced, disease incidence is notably higher in overweight individuals compared to people of normal weight.
To point, a study in the most recent issue of Obesity (same journal, 2 weeks later) examines the relationship of BMI with many measures of cardiovascular disease in healthy, athletic men. In this study, those on the lowest end of BMI in the normal range (18.5-22.5) had a much lower risk of dying from or developing cardiovascular disease than normal weight men with a slightly higher BMI (22.5-25).
Men with the lowest healthy BMIs also had lower risk of hypertension, lower cholesterol and half the risk of diabetes. While the length of this study was only 7.7 years (compared to the 12 years reported in the Times story), there were more than double the number of participants (28,776 vs. 11,834).
(Why did this story not make the news? My guess is that it makes for a less compelling storyline and people would rather not hear it.)
Mortality is certainly an important measure in any study, but it is arguably not the most relevant endpoint. Disease and excess body weight can severely impact quality of life, particularly for older individuals (as illustrated by another study in the latest issue of Obesity). While I cannot speak for everyone, it seems probable that quality of life is equally if not more important than longevity alone. Thus it is questionable how much stock to put into studies that ignore these other factors.
It is also critical to remember that BMI is a measure that was designed to describe people at a population level, not as individuals. While large cohort studies can tell us useful things about relative risk, they are not directly applicable to individual people.
The inconsistency of the data related to BMI and mortality may in fact be an indication of its inadequacy as a general measurement. Remember that BMI represents a ratio between height and weight, making it possible to compare people of various body sizes. Normalizing for height may, however, be deceptive.
Decades of data on caloric restriction consistently show that smaller body size (irrespective of body fat levels and, possibly, BMI) is associated with longer life and decreased risk of nearly all diseases. This is true in all animals from yeast, to worms and flies, to mice and monkeys. While humans are certainly different from all these model organisms, there is tremendous evolutionary precedent indicating smaller body size as the best for health.
The principle of parsimony tells us the simplest hypothesis–that smaller body size is beneficial–is probably correct. Substantial evidence must be accumulated before this hypothesis can be rejected, and I have yet to see that data.
Furthermore, while the research on the risk of overweight may be slightly ambiguous, the data on obesity is not. It is painfully clear that the dangers of obesity are profound and on par with those of smoking cigarettes. Overweight is a necessary step to becoming obese, and according to the National Population Health Survey nearly a quarter of Canadians who were overweight in 1994/1995 were obese by 2002/2003. Since overweight is still a substantial risk factor for becoming obese, misleading public health messages about the benefits of body fat are especially dangerous.
As a consumer of information, the most important thing you can do is be skeptical of what you read. Just because something is printed in the New York Times does not make it true. In fact, many of our most trusted sources of health information do not base their recommendations on rigorous scientific thinking, which is probably the reason for the health disaster we are currently facing.
Thanks to Jan from Quest for Health for sparking this discussion.
What does your gut tell you about the relationship between health and body fat?
Great analysis! It is unfortunate that many of these studies, which many times are meant for scientific research and are in context to other ongoing scientific research, are stripped from trade publications and are distributed by a mass media and are consumed by reporters, editors and consumers that do not have the specific scientific knowledge to question the study, or to fully comprehend the context of the study and its outcome.
In the past these studies remained inside the scientific community which allowed quality critique. With the internet and 500 TV channels along gobs of talk radio, mass media is on the constant lookout for a headline. It would be nice to allow a time for critique and analysis prior to the consumption by mass media, but I think the cat is out of the bag. All we can do as consumers is do as you said and “be skeptical of what you read”
Technically the peer review process of publication should handle most of the critique from the scientific community. Despite its imperfections it does a semi-decent job. But you are right that more analysis and followup would put new research into the context better and send a clearer message to the public.
I think the real problem is the reporters who base their analysis on a press release and a few interviews rather than true critical expertise. It is tough to demand post-graduate science degrees from our journalists, however.
You handled this subject extremely well, Darya! I agree with you – excess weight is never desirable from a health point of view. In his book, Eat to Live, Dr. Joel Fuhrman mentions 25 studies that state that lean people live longer. The evidence suggests that it is particularly abdominal fat that predicts health risks.
Hi Darya,
Thanks for bringing up this article, it’s an interesting one and I’ve been waiting for it to make a splash in the blogosphere! As usual you make some good points, and I would like to point out a couple things to help put this research in context. I apologize for the length, but it’s a topic near to my heart 🙂
The main issue, which was alluded to by Hanlie, is that BMI is a crude measure of body fat. More and more research, including most of the work that I have been involved with, has shown that it’s not how much body fat you have, but where you store it. For example, body fat stored in the legs has consistently been shown to protect against metabolic risk in longitudinal studies (I just published a study showing that lower body fat is associated with improved health in elderly men and women, which is available here). 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 what drives 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).
On that note, I respectfully take issue with your title, because this study does NOT suggest that body fat is healthy (even though research suggests that it’s not always unhealthy either, even in very large amounts). The current study suggests that high BMIs were associated with health, and that is very different from saying that body fat is healthy. It gets confusing because obesity is currently defined using BMI, but many people (myself included) are trying to get the focus off of BMI, because as you’re probably noticing, there are a lot of reasons why it is not an ideal way to define obesity.
I’d also like to point out that obesity is not always a death sentence, in fact the work of Steve Blair and others has shown consistently that obese and active individuals are healthier than those who are lean and inactive. This is probably partly because physical activity preferentially reduces visceral fat, leading to dramatic health improvements with little or no weight loss. In a similar vein, a paper just came out showing that even in individuals who are classified as “lean” according to their BMI, those with greater amounts of abdominal fat are at increased health risk than those who have lower amounts of abdominal fat.
And lastly, I’d just like to mention that just because a study causes some confusion, it does not mean that the study was poorly done, or that it is irresponsible. I know that it is strange and somewhat counter-intuitive that being obese can protect against metabolic risk if the fat is stored in certain locations, but it’s a consistent and accepted finding. Unfortunately there is a tremendous amount of nuance in body composition research, and that is hard for the mainstream press to properly articulate. People also have a lot of emotional investment in the “fat=bad” line of reasoning, but it’s just not that simple (which makes my life much more difficult).
So while the mainstream press coverage might fail to properly explain the research in context (as it usually does), I get worried when I see people attack the research itself, which as far as I can tell was well done, and delivered a finding that is not very controversial at all when viewed in context of other research.
I will now climb down from my soap box… 🙂
Travis
Thanks for your insight Travis!
Just so we’re all clear on this, my problem was with the New York Times using the word “protective,” not the science itself. Thanks for the clarification.
I assumed as much, but I couldn’t resist commenting on a body composition paper 🙂
Travis
Have you read Linda Bacon PhD’s research? It may interest you. She has published at least one study regarding the health and weight issue.
She also now has a book out based on her findings.