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There Is No Childhood Obesity Epidemic

So stop applauding Michelle Obama for reducing it!

Chuck Kennedy/The White House/Getty Images

Obesity Rate for Young Children Plummets 43% in a Decade” said the front-page headline of yesterday’s New York Times, in what the paper described as a “stunning” drop. The story goes on to summarize the latest findings from the National Health and Nutrition Examination Survey (NHANES), which is widely considered the gold standard in regard to national health statistics.

The new statistics appear in a paper in the Journal of the American Medical Association, reporting on the prevalence of adult and childhood obesity in the United States over the past decade. The really significant news from the study is that it provides further evidence that the so-called “obesity epidemic” appears to have ended: overall, obesity rates for both American adults and children remained statistically unchanged between 2003 and 2012.

These findings are consistent with broader international trends.  As Michael Gard notes in his recent book The End of the Obesity Epidemic, data from all over the world indicate that, over the past ten to 15 years, obesity rates have leveled off or declined among adults and children.

This is an awkward development for obesity fear-mongers, who as Gard and others have pointed out, have repeatedly claimed that within another generation or two the entire population of some nations, most notably the United States, would be fat. 

The claim that obesity is an epidemic phenomenon, and that its prevalence was on the way to approaching 100 percent, has always been crucial to the other claims of the anti-fat industry, most notably that today’s children will have shorter lifespans than their parents, and that obesity is as great a threat to public health as global warming.

There has never been any real evidence for these claims: life expectancy continues to rise, overall health continues to improve, and today’s young people are healthier than their parents were at the same age. Faced with these inconvenient facts, the obesity police have always argued that, while it’s true we’re not seeing the supposedly devastating effects of a heavier population at the moment, we will surely see these effects if present trends continue.

But for at least a decade now, present trends have not included an increase in the prevalence of obesity, either in America or in most other countries.  So why have people stopped getting fatter?

The answer is that nobody knows—and not in some exalted Cartesian sense that we can’t be certain of the true answer, but in the much humbler and humbling sense that no one has any idea.

This is not surprising. No one knows why the average weight of Americans was relatively stable in the 1960s and 1970s, or why it went up significantly in the 1980s and 1990s. We don’t know if people are more or less physically active than they were a generation ago, or if they ingest more or less calories.  Reliable data on these questions simply aren’t available. This has left the field wide open for endless impressionistic speculation, of the “when I was a kid we rode our bikes all day and didn’t play video games” type, in place of actual scientific analysis.

We do know that public health interventions designed to get people, and particularly children, to lose weight, have uniformly failed to achieve that goal. Again this is not surprising, since it would at a minimum be necessary to understand why obesity rates had increased before one could reasonably expect to design a successful intervention.

Which brings us back to the “stunning” result in the JAMA study, indicating that obesity rates among two to five year olds have plunged over the past decade. Not surprisingly, government agencies are promoting this statistic as possible evidence that Michelle Obama’s Let’s Move! campaign, which is celebrating its fourth anniversary this week, is having an effect.

But, as the authors of the JAMA paper themselves note, it’s important not to over-interpret this single number. First, whenever one looks at a much smaller subgroup of a large data set (two to five year olds represented less than ten percent of the study’s subjects) one is more likely to see relatively large percentage variations over time in regard to the prevalence of a characteristic.

So while it is true that the prevalence of obesity in two to five year olds declined by an estimated 39.6 percent between 2003-04 and 2011-12, from 13.9 percent to 8.4 percent, it is also true that, according to the same NHANES data, it declined by 23 percent between 2003-04 and 2005-06, and then rose by 19.8 percent between 2007-08 and 2009-10. 

The most plausible explanation for these large oscillations can be found in the definition of “childhood obesity” itself.  “Childhood obesity” is a brand-new concept, invented a few years ago for essentially political reasons. The official definition is that children who are at or above what was the ninety-fifth percentile of BMI for age in growth charts from the 1960s and 1970s are now classified as “obese.”

It is important to understand two things about this definition. First, it is quite literally arbitrary: it isn’t based on any epidemiological observation that this or that bad outcome is seen among children who are above this particular definitional cut point.  Public health authorities needed a definition for their crusade against a newly invented menace, so they made one up.

Second, tiny variations in average weight will have striking effects on the rate of “childhood obesity,” so defined. For example, in the 2011-12 NHANES data, a few dozen children weighing on average one pound less than their predecessors in the 2003-04 data would be enough to move those children from just above to just below the cut point, thus producing a “stunning” plunge in the rate of childhood obesity.

In short, the imposition of arbitrary definitions on public health statistics provides a far more compelling explanation for both the panic over “childhood obesity,” and the sudden triumph in the war against it, than any policy-driven behavioral changes among the preschool set.