Obesity shortens lifespan, BIG caveat

A recent newsworthy study in NEJM looked at Pima Indians, from their youth to adulthood, and the data suggest that being obese at a young age and having "pre-diabetes" increased the likelihood of early death.

But, this study was done in Pima Indians, and the Pima have long been known to have a severe predisposition to diabetes and obesity (they frequently show up in medical textbooks as the prototype for a population susceptible to type 2 diabetes); and Native American populations throughout the US and North America have a number of other serious co-morbidities (low socioeconomic status, high substance abuse rates, etc) that could make this study difficult to generalize to the rest of the US population, which of course is highly heterogeneous.

So, this study - targeting a very small and genetically unique population in the US - should be taken with a sizable grain of salt.