The mysterious weight gain

by Russ Roberts on January 5, 2010

in Health, Not from the Onion

This is from today’s New York Times (and not The Onion):

It is widely known that women tend to gain weight after giving birth, but now a large study has found evidence that even among childless women, those who live with a mate put on more pounds than those who live without one.

The differences, the scientists found, were stark.

After adjusting for other variables, the 10-year weight gain for an average 140-pound woman was 20 pounds if she had a baby and a partner, 15 if she had a partner but no baby, and only 11 pounds if she was childless with no partner.

You can debate how stark a difference that is–fifteen pounds vs. eleven pounds is the relevant comparison. You can argue that’s a big difference–it’s 36%. Or small–just four pounds. But what’s more interesting is the mysterious nature of this finding. Is it just me? Seems pretty obvious. But I guess the Times couldn’t find anyone who could explain it.

The Times continues:

There is no reason to believe that having a partner causes metabolic changes, so the weight gain among childless women with partners was almost surely caused by altered behavior. Moreover, there was a steady weight gain among all women over the 10 years of the study.

No, it isn’t metabolism. It’s probably a change in behavior. But what could explain why single women add less weight than married women over time?

The Times did find a doctor who offered an explanation of sorts:

“It’s interesting and brings out some important points,” said Maureen A. Murtaugh, an associate professor of epidemiology at the University of Utah who has published widely on weight gain in women. Perhaps, she suggested, a more active social life may help explain why women with partners gain more weight.

“Think of going to a restaurant,” Dr. Murtaugh said. “They serve a 6-foot man the same amount as they serve me, even though I’m 5 feet 5 inches and 60 pounds lighter.”

That’s quite creative. I don’t think that’s it, though. But I do like her explanation as a further window into how doctors think–obesity is something that happens to people like cancer. Here’s the causal chain for the obesity victim: married women socialize with their larger husbands, restaurants give the same oversized portions to big men as smaller women, ergo, women who are married gain weight. So the restaurant industry is the cause of married women gaining those four extra pounds.

It is an interesting and important hypothesis but my guess is that single women eat out more often married woman which is an awkward fact. I do think there’s a simpler explanation.

Here’s how the article ends:

Dr. Dobson [one of the authors of the study] said the finding of weight gain among all the women, with families or without, was troubling.

“This is a general health concern,” she said. “Getting married or moving in with a partner and having a baby are events that trigger even further weight gain.

“From a prevention point of view, one can look at these as particular times when women need to be especially careful.”

Yes, it’s dangerous being around food. It can just jump into you and the next thing you know, you’ve gained weight. Especially these days. It’s sort of like terrorism, I guess. We need a Code Orange for married people in restaurants. Maybe an announcement about unattended food or maybe attended food being dangerous.

What I like about my explanation is that you don’t need a Ph.D in economics to figure it out. The Times could have walked out of the office onto the streets of New York and asked a construction worker or a lawyer or even a journalist if they thought married women of a particular age and height weigh more or less than single woman of that age and height. And I just have a feeling that there’d have been a pretty powerful consensus that married women weigh more. Maybe I’m biased about how easy a question it is to answer. But it seems pretty obvious to me. I wonder how much that study cost and who paid for it.

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