

Monday, November 03, 2008

Obesity is a choice

Obesity is a choice. What a horrible thing to say! Let me put it more mildly: today I will argue that the claim "obesity is not a choice" is wrong.

Let's hear what Dr. Robert Lustig, pediatrician and obesity expert, has to say:



"Everyone's assuming you have a choice, but when your brain is starving, you don't have a choice," Lustig said. "When you look at it that way, all of a sudden Big Food looks like the perpetrator, and the patient becomes the victim. Congress says you can't sue McDonald's for obesity because it's your fault. Except the thing is, when you don't have a choice, it's not your fault."

Dr. Lustig has some valid concerns about the effects of insulin spikes from foods with high glycemic loads. But if there is some kind of psychological starvation response in the brain, overcoming instinct is still possible. I even consider it virtuous. So I accuse Dr. Lustig of overstating his case. There is evidence that obesity rates respond to incentives. If obesity rates respond to incentives, then there is choice involved (at least, for some people; this evidence only shows that some people alter their weight based on incentives).

First: marriage leads to obesity:
•Women in their teens and early 20s who continued to date but didn't cohabitate gained an average of 15 pounds over five years; their male counterparts added about 24 pounds.

•Newly married women in that age group packed on 24 pounds in five years; newly married men gained 30 pounds.

That degree of gain wasn't seen in couples who were living together but not married. Women gained 3 pounds more than their single peers — 18 pounds — and men gained 24 pounds.

"When people are dating, there may be more incentive to be thin," [Penny] Gordon-Larsen [an assistant professor of nutrition in the school of public health at the University of North Carolina-Chapel Hill] says.

I agree with Gordon-Larsen; the incentive to attract new partners is probably the cause. As your partner's commitment to you increases, the incentive to be attractive decreases.

Second: obesity is contagious.



The effects were generally larger between people of the same sex.





Maybe you face less social disapproval from your friends when they gain weight, so the cost of gaining weight is decreased. Alternatively - noting that the effects were larger between people of the same sex - it could be about competition. Maybe people try to compete with the norm for their gender, and their perceived norm is influenced by their social group.

Whatever the explanation, it appears that obesity is responding to incentives.

(Quick disclaimer: don't read into this post anything that isn't there. As far as I can tell, I have not said anything normative about obesity or social acceptance of obesity in this post.)


Blogger Stephen Whittington said...

What explains obesity rising significantly in the last 30 years then?

Tom Harford says it could be a rational response to much better medical treatments that mean we can live long and be obese.

8:53 PM

Blogger Michael said...

That explanation makes sense.

The post was intended to be narrowly focused, only attacking that argument without putting forward any explanation for obesity, nor taking responsibility for advancing any hypotheses.

But I've been asked to speculate, and I like speculating. I suspect increased obesity has been caused by a lot of things, many of which relate to incentives. They could include:
-The decreased cost of machine-powered travel vs. human-powered travel has decreased daily calorie expenditure.
-The decreased financial cost of food has led to increased caloric intake.
-The increased convenience/availability of food (e.g. 24-hour stores and delivered food) has decreased the "inconvenience" (as opposed to financial) cost of food, increasing caloric intake.
-Sedentary entertainment has improved (computer games; better TV; better board games) relative to athletic entertainment, decreasing the caloric expenditure that was incidental to those activities.
-Poor information about the effectiveness of low-fat+high-carb diets has led to some poor choices (this one does not relate to the incentives of consumers, but rather just to bad information).
-Decreased social disapproval of obesity has lowered the cost of being obese.
-Virtual socialization (such as internet-based and phone-based socialization) has offered alternatives to physical interaction where appearance matters, reducing the cost of being overweight.
-Various environmental/pathogenic/genetic factors may have decreased responsiveness to diet/exercise countermeasures, increasing the cost of lowering weight. (I suspect this last reason is highly dubious, but I'm aware that some people think this is the case.)

Or whatever. I'm not a dietologistician.

10:22 AM


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