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Healthy Fat? Higher BMI Linked to Lower Risk of Death
Across the globe, people of all walks of life are making similar New Year’s resolutions: Join a gym; lose some weight; fit into those skinny jeans — in other words, get healthier. But 2013 may be the time for rethinking what “healthy” means in the first place. New research suggests being slightly overweight is actually associated with a lower risk of dying. So is it time for a post-holiday cookie binge?
Researchers led by Dr. Katherine M. Flegel of the Centers for Disease Control and Prevention analyzed the link between Body Mass Index (BMI) and mortality in almost 100 studies from the PubMed and EMBASE databases. Combined, the studies included more than three million adults, and all studies adjusted for age, sex, and smoking habits.
People with a BMI between 18.5 and 25 were considered normal weight; those with BMIs over 25 were labeled overweight; a BMI between 30 and 35 meant grade 1 obesity; and anything higher than that meant grade 2 or 3 obesity. The results found that a little pudge had a protective effect: The overweight folks had a six percent lower risk of death, while those in the grade 1 obesity category had a five percent lower risk of death. But in this case, moderation really proved to be key: Anyone with higher than moderate obesity (i.e. the grades 2 and 3 obesity categories) had a 29 percent increased risk of death.
The study authors can’t say for sure that a higher BMI directly causes a longer lifespan, but they suggest there may actually be cardiovascular benefits and other positive health effects to a little extra body fat and higher metabolic reserves (energy the body has available to utilize).
Why It Matters
This research isn’t the first to suggest that a slightly elevated BMI is associated with a lower risk of dying . Similarly, studies find that being underweight actually increases mortality risk   . But there might be more at play than a simple connection between being overweight and having better health.
For one thing, the authors admit this particular study only looked at “all-cause mortality,” or death from any reason. There’s substantial evidence suggesting that being overweight or obese is a risk factor for diseases such as diabetes and cardiovascular disease  . “All-cause” obviously includes diabetes and heart disease, but if the study authors had looked at the rates of death from just those two health issues among people with different BMIs, the results might theoretically have shown that overweight and obese people actually had an increased risk of death.
Is It Legit?
Sorta. It’s possible that BMI just isn’t a great predictor of mortality risk or even health in general. BMI doesn’t take into account some important aspects of health, including blood pressure, blood sugar, and cholesterol. Some experts also point out that BMI doesn't say anything about a person's muscle mass. Other body measurements, such as visceral (abdominal) fat or fat distribution and waist circumference or waist-to-height ratio may give a better picture of a person’s health . People with larger waist circumferences and higher amounts of visceral fat, for example, usually exhibit risk factors for cardiovascular disease. Another, somewhat counterintuitive, idea is that overweight and obese patients are more likely to present health problems (such as diabetes) that require them to visit a doctor regularly, meaning whatever medical issues they have get treated.
So, for those whose resolutions had something to do with buying new running shoes or growing an affinity for brussels sprouts, keep at it. These results aren’t an incentive to let healthy habits fall by the wayside. Rather, this study serves as a call to continue studying the link between body composition and certain medical issues — and a reminder that our attitudes about what constitutes a “healthy” body might benefit from some expansion of their own.
Do you think someone’s BMI is a good indicator of his or her health status? Let us know in the comments below or tweet the author directly at @ShanaDLebowitz.
- Morbidity and mortality risk associated with an overweight BMI in older men and women. Janssen, I. School of Kinesiology and Health Studies, Department of Community Health and Epidemiology, Queen's University, Kingston, Ontario, Canada. Obesity 2007;15(7):1827-40.⤴
- BMI and mortality: results from a national longitudinal study of Canadian adults. Orpana, H.M., Berthelot, J.M., Kaplan, M.S. Health Analysis Division, Statistics Canada, Ottawa, Ontario, Canada. Obesity 2010;(18)1:214-8.⤴
- Underweight, overweight and obesity as risk factors for mortality and hospitalization. Ringbäck Weitoft, G., Eliasson, M., Rosén, M. Centre for Epidemiology, Swedish National Board of Health and Welfare, Stockholm. Scandinavian Journal of Public Health 2008;36(2):169-76.⤴
- A prospective study on the association between underweight and mortality from all cause. Qian, W., Guo, J., Zhang, W. Department of Cardiology, First Affiliated Hospital, Nanjing Medical University, Nanjing, China. Zhonghua Yi Xue Za Zhi 2001;81(19):1162-5.⤴
- Effect of BMI on lifetime risk for diabetes in the U.S. Narayan, K.M., Boyle, J.P., Thompson, T.J., et al. Division of Diabetes Translation, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia. Diabetes Care 2007; 30(6):1562-6.⤴
- Overweight and obesity as determinants of cardiovascular risk: the Framingham experience. Wilson, P.W., D'Agostino, R.B., Sullivan, L., et al. Boston University School of Medicine, Boston, MA. Archives of Internal Medicine 2002;162(16):1867-72.⤴
- Indices of abdominal obesity are better discriminators of cardiovascular risk factors than BMI: a meta-analysis. Lee, C.M., Huxley, R.R., Wildman, R.P., et al. Nutrition and Lifestyle Division, The George Institute for International Health, University of Sydney, Sydney, Australia. Journal of Clinical Epidemiology 2008;61(7):646-53.⤴
Comments Leave a comment
There are a lot of reasons why someone who is slightly heavier might live longer, though none of them would suggest you should actually strive to gain extra weight. A lot of diseases cause people to lose substantial weight because they can't eat or properly digest food, etc. Those people aren't at a higher risk of death because they're skinny, they're skinny because they're at a higher risk of death. Also, if an elderly person falls on their hip, someone with a little extra padding might only bruise, while someone with a healthy BMI might have a fractured hip bone. Again, the extra fat had nothing to do with cardiovascular benefits or however else you may try to justify these results, the extra padding just happened to be useful for an isolated event.
Hi, and thanks for your feedback! It makes sense that someone who's sick would be a lot thinner than normal, and that gaining weight wouldn't actually cause them to live longer. But it's interesting that you don't think a higher BMI is inked to cardiovascular benefits -- that's actually something the study authors mention in their paper. There's still a lot of research going on though, and it's possible that BMI isn't a good measure of a person's health at all. Let us know if you come across any other new research on the topic!@Delve Into Health
@ShanaLebowitz @Delve Into Health Most of what the paper says -- it's a meta-analysis, not a study -- is that they found correlations that overweight (a vague identifier, even in the confines of BMI) people lived on average 6% longer, but took into account almost no other bio-markers or other potential causes of death (or living). People with a healthy BMI can suffer from the same CVDs as those with 'overweight' through Grade 3 Obese BMIs, although the likelihood is much smaller. Subcutaneous at itself does serve many good functions in the body, such as organ fat that helps to protect against bruising, but there's a big different between maintaining a healthy fat ratio to being overweight. Most dietitians want people to focus on a better fat-to-muscle ratio because they understand where fat is useful and why, or where it's harmful (i.e. fatty liver disease, something typically only obese people get).
The study has many flaws, such as the overreliance on a single flawed metric like BMI. Remember, two people that weigh 220lbs at 5'11" will have the same BMI (they'd be at the upper-end of the 'overweight' scale, just a few decimal points from Grade 1 Obese), even if one is "fat" whereas the other is a bodybuilder. Using a single metric throws them both into the same category even though they're on the opposite ends of the health spectrum. A sensible doctor certainly would not tell the bodybuilder they need to lose weight or anything because their BMI is high, he could tell they're already fairly healthy, whereas the "fat" patient would receive a much different consultation.
Flegal published a similar study in 2005 -- expanded on in 2007 -- which was similarly flawed and discussed in the community and it seems that her and her team are continuing to focus correlational outcomes rather than causational ones.
I read about this study elsewhere. Didn't they conclude that this was a case of correlation, not causation? If you're sick, you lose weight. If you're sick enough, you die. Especially with the elderly. So, basically, people who are about to die from sickness get skinny. People who aren't about to die from being sick don't get skinny. And far more people die from being sick than from basics like heart attack or organ failure due to old age. Things like cancer and pneumonia. Being slightly overweight isn't what helps people live longer. Being healthy is. Being skinny doesn't kill you. What makes you skinny does.Correlation, not causation. In fact, in this case, causation is the reverse of what everyone seems to think about this study.
@Staleek Exactly. With this kind of study, there is no random assignment (I can't say, "Hello, welcome to my study. Today you're going to have an 'overweight' BMI and then I'm going to measure how long you life for.") so it's a Quasi experiment, which can only show correlation.