Childhood Obesity Levels Off, but What Does It Mean?

Don't pass the party snacks just yet.

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There's some not-bad news about childhood obesity today: A study published in the Journal of the American Medical Association finds that the prevalence of kids with a high body mass index, or BMI, showed no significant increase between 1999 and 2006.

If that trend is borne out in data for subsequent years, it's at least a sign that the upward creep of child BMI may have leveled off. But it's by no means great news, since it still means more than 16 percent of kids between 2 and 19 had BMIs at or above the 95th percentile, while about 32 percent were at or above the 85th percentile. I know—that looked weird to me, too: How can 16 percent of kids be above the 95th percentile? (It's like Lake Wobegon, where all the children are above average!) But those percentile charts are based on decades-old data on kids' weight; kids have gotten heavier in proportion to height, so now 16 percent of them are at or above the level that used to be the cutoff for the top 5 percent.

Even if the numbers have reached a plateau, that's still a lot of kids who need some help with their eating habits and exercise. My colleague Deborah Kotz wrote extensively about kids and weight last year, including a story on five comments parents should never make to their kids about weight.

And I've written about some of the flaws of using BMI as the measure of obesity, a topic addressed in an editorial accompanying the JAMA study. Childhood BMI is correlated with higher body fat and other risk factors for disease, the editorial authors write but cannot directly measure whether a kid indeed has high body fat or, alternatively, is heavier because of lean muscle mass. So it needs to be taken in context with other factors that may affect the risk of future disease—things like family history, physical fitness, diet quality, and racial or ethnic group.