Technical note: Contrary to what this Maxim article says, there's no particular reason to blame the "obesity paradox" on BMI versus body fat percentage.  It is surely the case that looking at body fat percentage as well would give an even more accurate picture, but the "obesity paradox" was debunked without doing so.  The recent study debunking it did so simply by using some high-quality data that avoided a lot of correlation-versus-causation problems that lay at the heart of the "obesity paradox". TL/DR: Illnesses often cause weight loss, so you need to look at weight history to see the health problems of being overweight. The "obesity paradox" generally arises from studies looking at people's weights at death or near death. Illnesses often cause people to lose weight.  For 300-pound sacks of lard, that rarely matters, because even if they're losing weight due to illness they'll almost always die long before reaching a healthy weight, and so they'll tally a mark in the "obesity/overweight kills you" column.  However, for sacks of lard that are "merely" overweight, it can happen all the time that they fall ill, lose 20 pounds, reach the normal BMI range, and die.  (There's a secondary issue that smokers are often thin and unhealthy, but I suspect it was possible to control for that well enough that it wasn't the main problem.)  Some studies tried to deal with this by asking sick/dying people or the families about the person's weight history, which I'm sure is about as accurate as asking whether they deserve a raise at work. The new study only considered people whose weight had already been tracked for 16 years.  Then it looked at deaths over a 12-year period following that.  It found that if you looked at the maximum BMI of a person during that 16 year period, "people" whose maximum BMI was overweight died more than people whose maximum BMI was normal, "people" whose maximum BMI was obese died even more often, and "people" whose maximum BMI was severely obese (or worse) died the most often.  (And people whose maximum BMI was underweight died more often than people whose maximum BMI was normal.)  Using people with a 16-year weight history as your starting cohort is just superb. You may wonder: did they really track people 28 years just for this?  No, people run long-term observational studies that generate data that other researchers can then use in their own studies.  This anti-"obesity paradox" study used this and this. One final note for former fats bothered by the "maximum BMI" thing: There are lots of studies that show that losing weight improves your health.  This doesn't contradict that.  It does suggest that you're worse off than if you never got fat in the first place.  Too bad: actions have consequences.  However, this study doesn't differentiate between, for example, "people" who started the 16-year period fat and ended it fat and people who started the 16-year period fat but maintained human status starting from year 5 (or whatever).  Therefore, there is no quantitative information about how much better off you are by losing weight and keeping it off, just quantitative information about how much better off you are by never getting fat (or technically how much better off you are by staying human for at least 16 years).