The following propositions are all true:
1. The Body Mass Index is a very crude measure of obesity, since it doesn’t distinguish among body types, distinguish fat from muscle, or distinguish abdominal fat from less harmful fat carried elsewhere on the body.
2. Carrying a little extra padding around after 40, as compared with currently published health standards (to say nothing of current fashion standards) seems to reduce mortality somewhat, though it may decrease quality-of-life in other ways.
3. Being obese, as opposed to mildly overweight, is really, really, really bad for you: bad at a level comparable to smoking, though not as bad as heavy drinking.
4. The country (leading the developed world in this regard, though probably only by a few years) is in the midst of an epidemic of obesity, especially juvenile obesity.
5. Bad diet and lack of exercise are the two main factors leading to obesity, though individuals obviously vary in their congenital risks of becoming obese.
6. The causes of bad diet and lack of exercise are diverse and poorly understood. Of course they are individual behaviors, but those behaviors are chosen within complex social contexts.
7. Walking and bicycling burn more calories than driving. Land use and transportation patterns that discourage walking and bicycling thereby contribute to obesity.
8. The food industries, and especially the convenience-restaurant and snack-food sectors, relentlessly market bad eating habits to children. It seems unlikely that their mult-billion-dollar efforts have no impact on actual behavior.
9. It’s likely, though not certain, that we could design and implement a combination of policy changes — regulations, taxes, and services — that would reduce obesity at acceptable costs in money and intrusion into private choice.
10. Attempting to use evidence about propositions 1 and 2 above to discredit propositions 3, 4, 8, and 9 is intellectually dishonest.
The entire exchange is worth reading, and conducted on a refreshingly respectful and serious level. Major points:
— Worrying about obesity easily morphs into making war on fat people. (Anyone who knows the history of drug policy has seen this pattern play out.)
— Exercise is good even if it doesn’t make you lose weight.
— Dieting is mostly bad for your health.
— Focusing on looks rather than health habits is unhealthy.
— Creating opportunities for, and habits and customs about, exercise may be as important as changing dietary habits and customs.
Lindsay is basically right: obesity is like global warming. In both cases, advocates of “doing something” oversimplify complex science, and advocates of doing nothing use compexity to obfuscate the existence of real problems.
Update Mike O’Hare asks:
Why does the BMI have units of pressure (lb./in^2)? And why is a properly inflated passenger car tire’s pressure about the same as a properly inflated person’s BMI?