The genetic limits of obesity.

Science, technology, and life.
June 5 2008 7:58 AM

Saturated Fat

The genetic limits of obesity.

Overweight couple
An overweight couple

Good news: Child obesity in the United States has stopped increasing. Government data analyzed in the Journal of the American Medical Association tell the story. According to a New York Times summary, "in 1980, 6.5 percent of children age 6 to 11 were obese, but by 1994 that number had climbed to 11.3 percent. By 2002, the number had jumped to 16.3 percent, but it has now appeared to stabilize around 17 percent."

William Saletan William Saletan

Will Saletan writes about politics, science, technology, and other stuff for Slate. He’s the author of Bearing Right.

Experts are jubilant. Here's the Washington Post:

"This lets us know that the epidemic is not an unstoppable epidemic and gives us hope our collective work can reverse it," said Risa Lavizzo-Mourey, president and chief executive of the Robert Wood Johnson Foundation, a private nonprofit group that helps fund anti-obesity programs. "It tells us that when we all work together—parents and schools, government, voluntary organizations, industry—we can make a difference."

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The Associated Press reports similar excitement:

Dr. Reginald Washington, a children's heart specialist in Denver and member of an American Academy of Pediatrics obesity committee, said "the country should be congratulated" if the rates have in fact peaked. "There are a lot of people trying to do good things to try to stem the tide," Washington said. Some schools are providing better meals and increasing physical education, and Americans in general "are more aware of the importance of fruits and vegetables," he said.

But wait: There's a problem. The stabilization may not be due to remedial interventions. According to the Times and other papers,

One concern is that the lull could represent a natural plateau that would have occurred regardless of public health efforts. "It may be that we've reached some sort of saturation in terms of the proportion of the population who are genetically susceptible to obesity in this environment," Dr. Ogden [the study's lead author] said. "A more optimistic view is that some things are working."

Bummer, huh? All that work we've been doing to teach healthy eating and exercise habits—irrelevant? Is the leveling off in child obesity just a product of genetic exhaustion?

I sure hope so.

I don't mean to dismiss the importance of changing habits. We'll need every bit of those changes to drive obesity back down to 1980 levels. But when you hear talk of making the world a better place, don't underestimate how much worse things can get. Job number one is to halt the frightening increase in fat. And the strongest ally we could ask for in holding that line isn't effort or education. It's genetics.

If, at 17 percent, we've hit the "saturation" point for child obesity, we're extremely lucky. There's no historical basis for knowing where the saturation point is, since our species has never before lived in an environment so full of ease and abundance. The far more dangerous possibility is that the saturation point is higher. In fact, given that we evolved in conditions of scarcity, it's logical to suspect that the tendency to seek and store fat is nearly universal. As the Los Angeles Times observes, "the idea that childhood weights have simply topped out doesn't quite square ... [One expert] said the fact that 60% of U.S. adults were either overweight or obese suggested that children had plenty of room to grow."

Two years ago, when I was researching the global escalation of obesity, I came across the work of Barry Popkin, an epidemiologist who studies obesity and hunger at the University of North Carolina. He's the guy who laid out the theory of how progress has changed our causes of death. In the hunter-gatherer era, if we didn't find food, we died. In the agricultural era, if our crops perished, we died. In the industrial era, famine receded, but infectious diseases killed us. Now we've achieved such control over nature that we're dying not of starvation or infection, but of abundance.

You want a really scary explanation for the plateau in child obesity? Part of it, according to Popkin, may be economic. "When economic times are difficult, we always slow things down on lots of things, like eating," he told the Post.

In other words, as the economy recovers and advances, so will obesity. And nobody knows where it'll end.

So let's stop "congratulating" ourselves for "trying to do good things" and "make a difference" in the fight against obesity. Let's pray that a force stronger than human will is behind the current stabilization. Doing good is less important than being well.

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