It was with great fanfare that the Journal of the American Medical Association (JAMA) released an article in January of 2013 that stated that you are less likely to die if you are obese! Well, that’s not exactly what the research said, but that didn’t prevent the popular press, such as The New York Times, from latching onto that headline and splashing it all over the internet.
The article itself was very scholarly. It was a meta-analysis* that examined BMI and the relative mortality risk. It analyzed 97 individual studies that included almost 3 million patients and 270,000 deaths. So the study itself was huge and well put together.
BMI categories were broken into the typical ranges: normal weight (BMI 18-25), overweight (BMI 25-30), Grade I obesity (BMI 30-35), Grade II and higher (BMI > 35). From there, they looked at mortality rates from all causes to arrive at their conclusions.
The conclusions of the study were that the overweight individuals (BMI 25-30) had a lower mortality rate than normal weight individuals (BMI 18-25). Those with Grade I obesity (BMI 30-35) had a similar mortality rate when compared to the normal weight individual. Grade II and higher (BMI > 35) was associated with an increased mortality rate when compared to the normal weight individual.
From these conclusions, all sorts non-sensical extrapolations appeared in the lay press and popular blogs. My favorite…maybe we should all gain more weight in order to decrease our relative mortality. Obviously, this is ridiculous, but people were saying things that the researchers weren’t saying and that the research couldn’t support. Allow me to point out two major problems (and a few minor problems) with taking this paper to that illogical end point.
First, the researchers used BMI as their measurement. At best, BMI is a crude tool. It does not measure health or fitness levels. BMI does not measure longevity or quality of life. In my opinion, BMI is useful as a physical descriptor, and it is useful when it correlates with the findings of a thorough history, physical, and lab work. It isn’t of much more use than that.
There are many people who are considered “overweight” by BMI standards but are actually incredibly fit and healthy. Even though the charts may say they are overweight or obese, they are actually at a good weight for them. Athletes with increased muscle mass are notorious for throwing off the BMI measurements.
Second, as the great philosopher George Strait would say, there’s a difference in living and living well. Just because you are alive doesn’t mean you have a good quality of life. As the saying goes, give me life to my years rather than years to my life. Most of us would rather have good health and full lives to the end. When my time comes, let me say my good-byes, and I’ll make a quick exit stage right. Languishing in bed for a decade is not the way most people would choose to go.
This research, while excellent research, did not measure quality of life- only mortality. We can’t make the assumption that just because one group lived longer that’s a good thing.
Other potential confounding factors for this research is that it addresses only all-cause mortality and not cause-specific mortality. It can’t take into account body fat distribution. Age was difficult to derive from the studies. And there is always the possibility of a publication bias (the tendency to publish only positive studies that support an idea instead of studies that are negative or inconclusive about an idea).
The take-home message for this manuscript is not to gain weight if you are at a normal BMI. Please don’t use this as an excuse to ignore your health. The appropriate conclusion is simple- don’t use BMI as your sole source of measuring your health. Don’t hyperventilate over the extra BMI points f you are otherwise healthy.
It’s been know for several years that there is a lower mortality among the overweight and moderately obese populations. The “why” is more difficult. Do these people seek medical care more often and more quickly? Does a little fat provide a significant cardioprotective effect? Do these patients have more “stored energy” that helps during illnesses and injuries? Until we have a better grasp on the “why,” it is difficult to make educated recommendations. Until researchers can make better recommendations the old recommendations still stand- follow a sensible diet, have a lifestyle of reasonably strenuous exercise, and have appropriate medical evaluations to head off trouble.
It’s always amazing to me how quickly the popular press picks up on research and then sensationalizes the headlines. This is a good example why you should read your newspaper, or the internet, with a skeptical eye.
* A meta-analysis is a way of combining several studies into a single huge study. It increases the power and accuracy of the individual studies and decreases the risk for biases in the research. A well-performed meta-analysis is considered one of the highest levels of evidence.