Surprising New Findings on Obesity

One of the first Freakonomics Radio podcasts we made was an episode about the (surprisingly tenuous) link between obesity and health problems. A new study in The Journal of the American Medical Association finds that “Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality.”  Writing for The Daily Beast, Kent Sepkowitz explains:

Compared to people with a normal weight (a BMI less than 25), the overweight (BMI between 25 to 30) had a 6 percent lower mortality rate—and both groups had a rate about 15 percent lower than the obese, especially the very obese (BMI above 35).

The explanation for the finding is uncertain. Perhaps the pleasantly plump but not obese have an extra reserve—a literal spare tire—that confers a survival advantage should they become seriously ill, whereas the lean-iacs do not. Or maybe the thin ones were thin because of a serious illness that, in the course the various studies, killed them. Or maybe the thin ones were thin because they were chain smokers living off Scotch and potato chips. Or just maybe the occasional pig-out does soothe the soul and make for a happier, healthier individual.

(HT: Andrew Sullivan)

Phoebus Rising

Sounds like Mr. Sullivan might be one of the "pleasantly plump".

Matthew V

I also remember seeing a study on BMI that showed various football players. Linemen and running backs (or some other position, don't like the sport) that had the same BMI, but completely different fitness levels had similar life expectancy. In other words, the fat guys and the fit guys lived to similar ages. Compared apples to oranges and got the same shelf life.

Rob S

Surprised this hasn't come up on Freakanomics, but isn't the mortality rate 100% for everyone?


Not yet. It's only 100% for those who have already died. Saying that it will be 100% (or indeed, any particular number) is predicting the future, which the Freakonomics guys keep telling us is impossible :-)

Eric M. Jones.


Predicting the future for the INDIVIDUAL is impossible. Predicting the certain future for a population is merely statistics.

That's why I know that you and everyone else will perish whilst I shall live forever.


Did the study take into account how the subjects died? Fit people may be more fit in general because they are more active. But going out and doing things puts you at a higher risk for accidental death than sitting on your couch watching TV...

Also agree with most here that BMI is far from an ideal way to measure health/fitness. Body fat percentage would probably be a better indicator overall.


Not only are there lots of superfit people with higher BMIs but there are lots of metabolically healthy and moderately fit people with higher BMIs. If someone is thin, no one assumes that they have to also be a bodybuilder to be basically healthy. Many studies through the years have also found that the same is true for fat people. This study of 3mil people also bares that out. Fat people do not fall into only two categories: coach potato or body-builder. Fat people lead the same lives as thin people: some are coach potatoes, some go to the gym 2-3 times per week, some walk to work and use the stairs, some play intramural sports, and some are in peak physical condition as professional athletes (bodybuilders, football players, Olympic judo or discus throwers, etc.).


"Fat people do not fall into only two categories: coach potato or body-builder."

Perhaps this is a quibble over your phrasing, but bodybuilders are seldom if ever fat. Competitive (male) bodybuilders typically aim for a body fat percentage under 6% (14-17% is considered normal for a fit male.)

That's really what most of the comments about the inadequacy of BMI as the sole measure of fitness have tried to address: the fact many who are moderately overweight by BMI can be carrying the excess as muscle rather than fat. Bodybuilders of course take this to an extreme.

Likewise, I'm sure we all have met a few slender couch potatos of the skin, bones, and small pot belly variety. BMI may say that these folks are at a normal, healthy weight, but are they really? Would they not be much healthier if they started working out and put on some muscle mass?


The results may be quite different if body fat % was used rather than bmi. Bmi is a notoriously poor method of gauging if a person is truly overweight. Tim Ferris wrote a great critique of bmi and is worth reading (I think it can be found on his blog). Bmi was originally developed as a statistical measure that makes generalizations about a population but was not intended for evaluation of an individual's body fat %.

Henry Lahore

Vitamin D is a possible reason. The extra weight stores vitamin D as well as calories. Many studies have shown that as a person gets sick and loses weight, the vitamin D levels in their bodies increases. The higher level of vitamin D protects the lower weight body against a wide variety of diseases.


My explanation: some of us are genetically programmed to be plumper, and it's "normal" for us. Unlike the morbidly obese, who clearly suffer from a syndrome we'd rather blame them for then explore and treat, we "plumps" are "as we should be." I have been in the neighborhood of 200 pounds my entire life. I'm now 66. I have no more health problems than the average person. It's foolish to think that human variation is so narrow that only "thin" is healthy. To puncture other myths, I don't live on chocolate cake and "choco covered sugar bombs" cereal. I eat a lot of vegetables and fruits, try to stick to whole grains, and prefer plain meats to "smothered in" kinds of dishes. I am as my grandmother was, and she died at 87.