There is very little evidence that obesity is harmful to young children. So I have to ask why NYC’s Department of Health and Mental Hygiene feels so strongly that fat schoolchildren should be forced to slim down. And why it’s so eager to congratulate itself today on its policing of eating behavior — see reports by WSJ, Bloomberg, CBS (with photos of fat kids!), Huffington, and many other sources. Why would the city’s health agency lie in order to claim that its jihad against a not-very-convincing evil has been successful?
The subject is a report published by CDC today claiming that obesity among NYC schoolkids in grades K through 8 has decreased 5.5%.
The city’s health commissioner, Thomas A. Farley has been true to the shades of history’s empty-headed warriors. Farley announced that the drop in obesity prevalence is a “turning-point in the obesity epidemic” although it “does not by any means mark the end.”
A missed photo opp: Dr. Farley standing on top of a fat child, holding up a sign reading, “Mission Accomplished.”
Farley is zealous about controlling people’s behavior and contemptuous of facts (nobody will ever accuse him of being an intellectual, either). He blogs about his own work for the exclusive reading pleasure of Department of Health staffers. This allows his staff to read the Farley-esque twist on truth. One example for now: in October of 2010, Farley’s blog exultantly told his staff that in 2009 the department had “immunized nearly 130,000 children [against flu] in more than 1,200 schools over a few months.” Of course, health department employees are smart — many of them knew that the 2009 H1N1 vaccine Farley was talking about was a fiasco, far too late to make a difference, and aimed at an outbreak that was more of a whimper than a bang.
What about today’s “turning point” in the obesity war? It’s worth noting that the supposed drop in obesity among NYC schoolkids is really just a very slight (1.2%) difference in the prevalence of obesity between 2006-7 and 2010-11.
A small difference between small numbers amounts to a large percentage difference. So the 1.2% actual difference magically turns into the advertised 5.5% — the proportionate change.
But the false advertising gets worse
1. The prevalence of obesity in NYC was not measured multiple times on the same group of kids (to use epidemiology jargon: this wasn’t a panel study). Nobody observed fat children becoming less fat. The city simply measured obesity prevalence each year on 5- to 14-year-olds who were in the school system. So a high proportion of the 21.9% of kids who were labeled obese in 2006-7 would have been out of the age range for the 2010-11 assessment.
Plus, lots of kids leave the NYC school system after grade school (this has to do with Bloomberg administration’s bizarre system for preventing children from attending local schools). So, even those children who haven’t aged out of the analysis by turning 15 would be absent from the data after a few years. And, there’s also natural immigration and emigration.
Did the 2006 fat kids get slimmer? Nobody knows. The 2006-7 obesity prevalence among NYC schoolkids (21.9%) can’t be compared to the 2010-11 prevalence (20.7%). If you were forced to compare these numbers, you’d say there had been a slight change — not a 5.5% decline. There’s the first lie.
2. The second lie is a little more complicated. Since there is no widely accepted functional definition for childhood obesity, children are labeled obese if their body-mass index (BMI) falls into the upper 5% of the expected distribution of weight-for-height. This expectation is based on an old-fashioned standard. Fair enough. But lots of distributions shift over time — SAT scores, human height, grades awarded at Ivy League colleges, and global average temperature, to name a few.
Sometimes the reason for an overall shift of this sort isn’t hard to specify (test prep, nutritional quality, relaxation of grading standards, generalized global warming, etc.). But the main effect causing a shift in the distribution doesn’t explain why the few people who are in the upper reaches of the distribution are so far from the mean. To say that fewer children are now above the high-BMI cutoff than in 2006-7 therefore the tendency of children to be fat is declining is a lot like claiming that because 2011 was cooler than 2009 and 2010, global temperatures are not really going up.
(Dr. Farley, I gather that statistics aren’t your strong suit, but surely when you witnessed that snowstorm we had this past October — an outlier if there ever was one — you didn’t conclude that the climate is actually getting colder, not hotter. So what makes you think that a very tiny decrease in the proportion of kids with high BMIs means that the city’s kids are getting slimmer?)
3. Claiming credit. Attributing to the health agency’s own efforts a minuscule change in the proportion of kids who are in the upper tail of the broad BMI distribution requires self-congratulation so acrobatic as to stretch credulity.
Maybe there really has been some change in the city’s children since 2006. Or in our food supply or buying habits. Or exercising. But to claim that such a change both caused the tiny decline in schoolkid obesity prevalence and that it was the result of the Health Department’s efforts — the exercising and the low-fat milk and the salad bars in the school cafeterias and so forth — is to commit the fallacy that Rene Dubos outlined (in his book Mirage of Health) nearly 50 years ago:
When the tide is receding from the beach it is easy to have the illusion that one can empty the ocean by removing water with a pail.
Is childhood obesity really a health problem?
It’s not crazy for health professionals to be concerned about body mass. Obesity might be really bad for some people, and somewhat bad for many.
But those people are adults. Why are health agencies like NYC’s so riled up about obesity in little children?
So far, there’s no strong evidence that obesity in younger children predicts any real harm later in life, other than being a fat adult. With adults, several signs of impending debility are more commonly found in the obese than the non-obese, such as hardening of the arteries, fatty liver, sleep apnea, and diabetes. And with adolescents, there’s some evidence that those who are obese develop similar warning signs. But not younger kids.
A 2005 BMJ paper reported only social effects in adulthood (being unemployed and being without a romantic partner) of early obesity. Similarly, one cohort study carried out in Newcastle upon Tyne found little evidence that fat children became fat adults, and no evidence for predictors of illness in adulthood among those who had been overweight as children — although other studies have shown correlations between adolescent obesity and adult problems.
For kids below age 15, the most visible problem with obesity is that it occurs most commonly among the poor and dark-skinned. This bothers the obesity warriors. In fact, not only is obesity more common in African- and Hispanic-American children in NYC, even the slipshod standards of today’s report on NYC schoolkids can’t be manipulated to show that obesity is declining among these children.
As with all holy wars, from the Children’s Crusade through the U.S. invasion of Iraq, the warriors aren’t really concerned about principle. Something about somebody got under their skin.
Here’s how I answer my own question: I guess the obesity crusaders don’t like it when the children of the wealthy look like the children of the poor. They think that white kids on the Upper East Side aren’t supposed to look like kids who live in the Bronx.
It isn’t about health, in other words. It isn’t even about obesity. The “childhood obesity epidemic” is about making sure society looks the way that the health crusaders want it to look.