Why we're fatter.

Health and medicine explained.
July 13 2006 12:46 PM

Why We're Fatter

Five reasons you haven't thought of.

(Continued from Page 1)

T.J. Wilkin and his colleagues at the Peninsula Medical School in Devon, England, looked at three groups of English and Scottish children. They measured physical activity using accelerometers, devices that record duration and intensity of movement 600 times a minute. The idea was to determine whether total daily activity level is essentially invariant for any one child—"in her nature," as my mother would have said—or whether it can be increased if a child goes to gym, walks to school, or doesn't watch television. Wilkin and his team also tracked whether children's daily activity level varied between weekdays, presumably spent sedately in school, and weekends, presumably spent going wild. If the total amount of expended energy remained constant despite the typically different structure of a weekday vs. a weekend, then it would suggest that daily total activity level is determined by something internal and specific to each child. (Do adults have an internally regulated daily activity level, too? I wish I could tell you, but we have no idea of the answer yet.)

The results of Wilkin's study would have brought despair to the many gym teachers who made my childhood miserable. Their efforts, it turns out, were for naught: Sluggard I was, and sluggard I was doomed to be. Wilkins and his team found that every child has his or her own very consistent daily level of activity. It remains the same on weekends and weekdays; it's not affected by school physical education, or by whether the child walks or drives to school, or how much time he spends awake or in front of a television. We don't know what determines this intrinsic level of activity. But engineering the environment to make available or even to require more activity will apparently have little impact on children whose nature is to be inactive.


All this makes me feel a bit vindicated. The medical students and residents I teach are chronically frustrated (and not a little angry) that my contribution to their education about managing obesity is often unhelpful and discouraging. Having read these new studies, I'm more depressed than ever.

Before we write off obesity as a hopeless problem, though, one more thought: As worried as I am about many of my heavy patients, I often do see heartening improvement, especially in later adolescence (even if I am skeptical that I played a role). The critical question is why some young people thin down while others do not.

I don't have an answer, but I do have an impression. It's that adolescents who lose weight are more likely to have acquired a positive sense of themselves, because they've had some academic or athletic success, or some other notable accomplishment. Sometimes they have embarked on a successful romantic relationship. And often parents and other adults in their life focus on their strengths rather than harping on weight and appearance.

I feel particularly moved to say this now because of a troublesome development on the horizon. The Centers for Disease Control and Prevention, the American Academy of Pediatrics, and the American Medical Association are talking about renaming degrees of fatness in children. Up to now, the heaviest children have been called "overweight," and the next heaviest group classified as "at risk of overweight." The tough-love talk being bandied about is that we should tell it like it is, and call obese obese. I don't think so. The impulse to rename reflects doctors' frustration at their inability to help heavy children: If we can't help them, then it's time to blame them. If I'm right, however, calling heavy children "obese" is likely to do the opposite of what we want, by making them feel worse about themselves.

Correction, July 14: The original sentence stated that David Allison and Scott Keith work at the University of Alabama. In fact, they work at the University of Alabama at Birmingham, a separate university. Click here to return to the corrected sentence.



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