Obesity, self-discipline, and stigma.

Last week, I wrote about obesity as a failure of self-discipline. A lot of you wrote back to let me have it. In the Fray, blogs, and e-mail, you told me I was wrongheaded and just plain mean. Some of this is miscommunication, but it's my fault. I was trying to explain something important, and I botched it. Let me try again.

The topic was a study published in the New England Journal of Medicine. It documented weight trends in a social network originating in Framingham, Mass. What the study illustrated, according to its authors, was "psychosocial mechanismsof the spread of obesity" through "a change in [one's] perception of the socialnorms regarding the acceptability of obesity." As your friends get fat, you start to think their degree of fatness is OK for you, too.

That's the important point. Now let's talk about what it means—and doesn't.

1. It doesn't mean you should ditch your fat friends. The study's implication, as I described it, is that "if you find yourself caught in a fattening social network, you have three options. You can resist the fattening norm. You can try to reverse it. Or you can ditch your fat friends." The authors discouraged the ditching option on the grounds that friendship is good for your health. Instead, they suggested, you should spend more time "forming ties with underweight or normal weight friends."

Ugh. This is a classic case of scientists inventing the kind of argument they're comfortable with—a scientific one—for what's really a moral point. The invented argument is well-intended but bogus. If you spend more time with "underweight or normal weight friends," you're spending less time with overweight friends. That's a mathematical and social fact, just like more time at the office means less at home. Nor does the healthiness of friendship require you to keep your fat friends. By trading them in for thinner friends, you'd end up with just as many friends as you had before. So, I made those points, because I don't like deceptions.

Then I did something stupid: I ended the piece. I neglected to spell out what I assumed: You shouldn't ditch your fat friends anyway—not for health reasons but because the point of friendship is that you don't go around ditching your friends every time that might be "in your interest." Your friend may develop an addiction, fall on hard times, or get a disease. Standing by him could become inconvenient in lots of ways. Do it anyway, because a person is more than his wealth or his disease and because friendship is more than convenience. If your friend develops something harmful and remediable, such as an addiction, you should help him fight it. That's what I was clumsily trying to say.

2. It doesn't mean all fat is acquired through lack of discipline. Some fat, as I explained last week, is genetically or environmentally induced. But I added that

such factors can't account for the spread pattern documented in this study. Genetics can't explain it, since having a fat friend was more likely to predict a person's obesity than having a fat sibling was. Environmental constraints can't explain it, since faraway friends made a difference, while next-door neighbors didn't. Availability of food can't explain it, since friends had a bigger effect than spouses did.