While there is little doubt that obesity can have negative health effects, the topic of how being overweight (between a healthy weight and obese) can impact a person’s life span. A recent meta analysis has proposed that being overweight, even by a few pounds, can lessen longevity. This contradicts a 2013 analysis which says being overweight can potentially result in a longer life expectancy and that low level (“grade 1”) obesity doesn’t have an impact on life span.
In Brief: The Obesity Paradox
There is a lot behind the idea of the “obesity paradox” and getting the full picture is somewhat complex, but a brief summary is possible based on current understandings. Obesity (and to a lesser extent, being overweight) is a risk factor for various chronic ailments like diabetes or coronary heart disease.
Once someone actually has one of these problems, however, being overweight or obese seems to let them live longer than a normal-weight person with the same condition. The strength of this effect goes down as weight goes up. Some studies have also found that simply trying to lose weight, even if unsuccessful, could improve life expectancy. This suggests fitness as well as fatness may be at play. If you are getting confused, just know that feeling is a feature, not a bug, of this topic.
The researches took data from 239 studies across several continents and pooled and re-analyzed the data. The result was that being overweight or obese was strongly correlated to higher death rates from cancer, heart disease, stroke, and respiratory disease. This seems to contradict a 2013 meta-analysis, seen here, which implied the opposite. The truth is that both findings may actually be correct, and the structure of this most recent analysis can explain how this could be possible.
The key thing to know about the obesity paradox is that it is primarily seen in people who have chronic ailments like diabetes. This most recent meta analysis specifically excluded participants who had a chronic disease or were smokers at the time the study started. The reasoning behind this move—that the conditions themselves could affect weight and skew the results—may or may not be valid depending on interpretation. A more important takeaway, however, is that this means the populations of this analysis would have differed significantly from the 2013 study as a result.
In other words, by excluding participants who had chronic conditions, the researchers also excluded the main circumstance under which being overweight or obese is known to have a protective effect. It is not entirely surprising, then, that they got the results they did.
What This Means
As mentioned, this study doesn’t necessarily contradict or counter the 2013 analysis. The obesity paradox is a nuanced topic that will inevitably show different life span impacts in different circumstances. The idea that populations which have smaller amounts of chronic disease will see less benefit from being overweight is still compatible with the 2013 findings, as both studies represent different angles of a multi-faceted subject, and this doesn’t even include the various quality-of-life problems weight can induce.
Vuong, Z., “New study has dire warning: Even a few extra pounds can kill you,” USC News web site, August 29, 2016; http://news.usc.edu/106147/new-study-has-dire-warning-even-a-few-extra-pounds-can-kill-you/, last accessed August 30, 2016.
Di Angelantonio, E., et. al., “Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents,” The Lancet, 2016; http://dx.doi.org/10.1016/S0140-6736(16)30175-1.