dear andrew perrin: i was wrong and you were right on the obesity and mortality correlation
A while back, Andrew and I got into an online discussion about the obesity/mortality correlation. He said it was true, I was a skeptic because I had read a number of studies that said otherwise. Also, the negative consequences of obesity can be mitigated via medical intervention. E.g., you may develop diabetes, but you can get treatment so you won’t die.
The other day, I wanted to follow up on this issue and it turns out that the biomedical community has come up with a more definitive answer. Using standard definitions of obesity (BMI) and mortality, Katherine Flegal, Broan Kit, Heather Orpana, and Barry I. Graubard conducted a meta-analysis of 97 articles that used similar measures of obesity and mortality. Roughly speaking, many studies report a positive effect, many report no effect, and some even report a negative effect. When you add them all together, you get a correlation between high obesity and mortality, but it is not true at ranges closer to non-overweight BMI. From the abstract of Association of All-Cause Mortality With Overweight and Obesity Using Standard Body Mass Index Categories: A Systematic Review and Meta-analysis, published in the 2013 Journal of the American Medical Association:
Conclusions and Relevance Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality. The use of predefined standard BMI groupings can facilitate between-study comparisons.
In other words, high obesity is definitely correlated with mortality (Andrew’s claim). Mild obesity and “overweight” are correlated with less mortality (a weaker version of my claim). The article does not settle the issue of causation. It can be very likely that less healthy people gain weight. E.g., people with low mobility may not exercise or take up bad diets. Or people who are very skinny may be ill as well. Still, I am changing my mind on the basic facts – high levels of obesity increase mortality.