Obesity Apocalypse

Even by the remarkably mendacious standards of the “obesity” racket some of the claims in this story are beyond belief.

The most laughable is the idea that by 2048 everybody in the US will be “overweight” or “obese.” This result was derived via statistical extrapolation, the crack cocaine of social science analysis (by similar methods one could prove that within a few generations Olympic sprinters will be running at speeds that will hurl them into low Earth orbit and everyone in America will have a plasma TV seventeen miles wide).

In fact there has been no weight gain at all over the past 30 years in the thinnest quartile of the population — whatever (poorly understood) factors have caused Americans to weigh more on average now than they did in the 1970s have had very different impacts across the weight spectrum: thin people have gained no weight, people in the middle weigh 10-15 pounds than they did 30 years ago, while the fattest people have gained a lot of weight, which is exactly what one would expect. Furthermore, as even this story manages to note, there’s quite a bit of evidence that the trend toward weight gain in the populace in the 1980s and 1990s seems to have plateaued.

But this is a side point. The most significant and symptomatic aspect of this story is it’s completely uncritical attitude toward the current definitions of “overweight” and “obesity.” Those definitons are BMIs of 25-29.9 and 30+ respectively. (You can look up your own BMI here, and I encourage you to do so).

I really can’t emphasize enough how utterly without scientific foundation these definitions are. This can be shown in a hundred ways, but here’s one particularly striking illustration.

The best epidemiological data on the U.S. population is the CDC’s National Health and Nutrition Examination Survey (NHANES). This is universally recognized as the gold standard for such surveys, in particular because it’s a nationally representative sample that directly measures its participants. NHANES has been ongoing since the 1960s; the most recent data that allows for significant followup is from NHANES III, which was assembled in 1988-1994.

Now if we’re facing an “apocalypse” because of “overweight” and “obesity,” we should see evidence of this in, at the very minimum, increased relative risk of mortality among people in these categories. Here’s the relevant data from NHANES III on mortality risk. The following statistics use the mortality risk found among supposedly “normal weight” (sic) people (BMI 18.5-24.9) as the referent group. In other words, the mortality risk for this group sets the baseline for comparison to other groups in terms of their mortality risk. A group that has a higher mortality risk than the referent group will have excess deaths over the baseline risk. A group that has a lower mortality risk will have fewer deaths than would be seen in the group if it had the same mortality risk as the referent group of “normal weight” people.

Most recent excess deaths estimates from NHANES III:
Underweight: 38,456
Normal weight: 0
Overweight: -99,980
Obesity Grade I: -13,865
Obesity Grade II and III: 57,515

Underweight less than 18.5 BMI, normal weight 18.5-24.9, overweight 25-29.9, Obesity Grade I 30-34.9, Obesity Grade II and III 35+ What these numbers mean: In the US population at present, we are seeing about 100,000 fewer deaths per year among “overweight” people than we would if “overweight” people had the same mortality risk as “normal weight” people. Note that the majority of people in the US who according to the government’s current classifications weigh too much are in this group. The “overweight” category is to the obesity panic what marijuana use is to the drug war: stories about an “epidemic” of fatness depend crucially on classifying the 35% of the population that’s “overweight” as being at some sort of increased health risk. This is simply false, and is known to be false by the researchers who are quoted in stories like the one linked above.

But the situation is much more egregious than even this suggests. Note that the NHANES III data reveals that most people who are classified as obese have a lower mortality risk than so-called normal weight people. About two-thirds of “obese” Americans have a BMI of between 30-34.9, and currently we’re seeing about 14,000 fewer deaths per year in this group than would be expected if the group’s mortality risk was the same as that of “normal weight” individuals.

Only when one gets to roughly the fattest 10% of the population does the NHANES III data begin to find a relative mortality risk higher than that found among the supposedly “normal weight.” And even here, the relative mortality risk results in about three times fewer deaths per capita than observed among the “underweight” (there are approximately four times as many people with BMIs 35+ than there are people with BMIs below 18.5).

In short, it’s difficult to convey the utter intellectual bankruptcy of the standard discourse surrounding weight and health in this culture.

Update addressing a couple of common themes in these sorts of discussions:

(1) I don’t think that the higher mortality rate among “normal” (sic) or “optimal” (sic) weight people provides any real evidence that someone with a BMI in that range should try to gain weight. The bogus idea here is that a narrow range of weight is optimal for all people. In fact the differences in mortality across an extremely broad range (roughly BMIs from the high teens to the mid-30s) are statistically trivial, and represent the kinds of differences in relative risk that nobody would ever pay attention to if not for cultural considerations that make body mass a subject of great symbolic (though not medical) importance.

(2) It really is astonishing how ready people are to accept the most dubious evidence for the proposition that everybody should try to be thin, while engaging in sophisticated arguments about why evidence to the contrary can be explained away. That this blatantly inconsistent attitude is characterized as the essence of science is also rather remarkable.