Jennifer Lovejoy, PhD, Senior Vice President, Clinical & Quality Support
Has our society over-emphasized the dangers of obesity, in a fear of fat that is not well-founded in evidence? This is the question recent news reports have raised about a new meta-analysis of the association between BMI and mortality (death) rates. While the study found the expected positive association between obesity and mortality, reporters have jumped on a secondary finding of the analysis, which is the inverse association between overweight and mortality that is, the finding that people who are overweight may sometimes live longer than those who have a BMI in the normal range. So does this mean we need to lighten up and stop encouraging people to lose those extra pounds? Its easy to see how the media could come to this conclusion, citing overreaction on the part of physicians and public health advocates, but a closer look at the study shows theyre missing the point entirely.
The Study Results
The recent study combined data from 97 different published studies conducted around the world (KM Flegal et al., JAMA 309:71. 2013). Overall, the analyses included over 2 million individuals, and over 270,000 deaths from various causes. The results showed that, relative to normal weight (BMI 18.5-25), people who were overweight (BMI 25-29.9) had 6 percent lower mortality. People who were obese (BMI>30) had 18 percent higher mortality. However, when the category of obesity was broken down further, only those with BMI greater than 35 had significantly higher mortality than the normal weight population.
One of the strengths of systematic reviews and meta-analyses is the large number of patients that can be included in the analysis to confirm (or deny) health trends. However, there are also limitations. Authors must decide which studies to include or exclude, and sometimes there is a disagreement about the criteria used to make these decisions. In this case, the decision to include studies from around the world, when many experts feel that U.S. categories for BMI do not apply to developing countries or non-white ethnic groups, may have contributed to bias in the results.
The authors of the study note that individuals who are overweight may have lower mortality because they get better medical care, because they show symptoms of disease earlier, or because theyre screened more regularly for chronic diseases stemming from their weight, such as diabetes or heart problems than those of a normal weight. Most importantly, we should recognize excess weight takes a number of years to cause health problems. It should not be a big surprise that mild degrees of excess weight dont cause higher mortality.
Why Employers Should Care
What do these new findings mean for your bottom line and decisions about workplace weight management programs?
What is most relevant to employers is the fact that even moderate degrees of excess weight cause increased health risk factors and early development of chronic diseases that drive high healthcare costs. For example, the risk of developing type 2 diabetes increases significantly at a BMI as low as 24. Knee osteoarthritis and back pain similarly increase with very modest amounts of excess weight. And high blood pressure can occur with as little as 20 pounds of excess weight.
So, the bottom line for employers is that this recent report about obesity and mortality, first, isnt a big surprise and, second, really doesnt mean much for how you should approach worksite weight loss. Its not increased mortality but increased chronic diseas