Obesity and Mortality
Update
Since our original publication of this series in December of 2004, one more study has been published that has been widely publicized in the press. Reference 10 has been widely reported to support a hypothesis that some degree of overweight is actually healthy - that is, if one is mildly overweight, mortality is slightly decreased. For the record, we note that previous studies, as we have summarized them in this series, have not made any claim concerning increased or decreased mortality due to being mildly overweight - the data are statistically inconclusive, even though one of the major studies tracked one million people over 14 years.
The new study (Reference 10) tracks roughly 37,000 people for about 12 years, so one would not expect it to be more statistically conclusive. Indeed, the results presented in this new study really only allow the conclusion that obese people (BMI above 30) have an increased risk, and that people who are overweight (BMI between 25 and 30) do not exhibit an increased risk of mortality. However, this last conclusion (lack of risk for overweight people) is questioned in reference 11, an editorial in the same issue of JAMA. The editorial notes the difficulties associated with separating the role of obesity form the role of other factors leading to mortality, and questions whether this is the reason for different conclusions in different studies.
Given the varying results between different studies, it is clearly evident that obesity (but not necessarily being overweight) increases the risk of mortality. Another way to look at this is to say that if two and more large studies could not find an increase in mortality due to being overweight, it clearly cannot be a large effect that people should worry about.
There is one other interesting result in this study - very thin people (BMI less than 18.5) have an increased mortality risk, between 1.5 and 2.0, compared to people with a normal weight. This contradicts advice based on animal studies (e.g., WebMD) that suggest that eating 20-40% less calories has significant health benefits. However, it is possible that both results are correct... If healthy people consciously eat less, they become more healthy. However, the very thin people in this study may have been thin in part because of some significant illness. So our suggestion would be to eat a Mediterranean Diet, enjoy life, and be healthy!
Obesity and Mortality
Update2, August 2008
A new paper just published, Reference 17, presents results from the English Longitudinal Study of Ageing (ELSA). 3793 participants aged 65 and older followed up for 5 years. The study concludes that obese people are more likely to be physically impared. For example, men had relative risk ratios of 1.99 (Margin of Error 1.42–2.78). They claim to find no increase in mortality. However, the risk ratio for mortality is indeed 0.99, but the large margin of error (0.6 to 1.6) easlily accomodates up to a 60% increase in risk in agreement with previous studies.