My ignorance of popular culture has once more been exposed by alert readers of this blog. I had never heard of Chris Farley. I have now looked him up on Google Images. I get it.
Several comments suggest that I ignored the biological basis of obesity. Let me clarify. Of course obesity is a biological phenomenon (though also a social one to the extent that in our society "obesity" carries negative connotations). I meant only that, since human biology changes only very slowly, changes in human biology can't explain the recent increases in obesity. But the biological foundations of obesity do require more emphasis than I gave them. In what evolutionary biologists call the "ancestral environment," a period ending some 20,000 years ago when our biological development reached approximately its current level, a genetic propensity to eat as much high-calorie food as possible had great survival value because the food supply was uncertain, and high-calorie food converts to fat that people can live off for a time if they have no food. When the good supply becomes assured and people become sedentary, they continue wanting to eat high-calorie foods because that is a genetic predisposition. They can avoid becoming fat by eating less than their genes tell them to, as it were, but this--fighting the genes--requires great self-discipline. It is much easier to control one's weight if one is physically active, in effect recreating the conditions of the ancestral environment in the gym or equivalent. But that is costly, especially in time.
Biology plays a further role. Differences in biology between people make it much easier for some people than for others to control their weight, sometimes without any exercise. This blurs the value of thinness as a signal of trustworthiness as a result of having a low discount rate.
Notice, as a curious historical note, that as late as the nineteenth century obesity was taken as a signal of prosperity and attractiveness, and thinness (including of women) was taken as a signal of poverty and ill health. This was because poor people tended to be undernourished and hard working, and tubeculosis and other wasting disseases were disproportionately diseases of the poor. Since food was expensive and leisure a privilege of wealth, being fat was a sign of success and valued accordingly.
I may have been precipitate in suggesting that reducing obesity would not affect aggregate medical costs. What I had in mind is that because on average a very high percentage of one's total lifetime medical costs are incurred in the last few months of life, and because the older one is, the greater on average one's medical needs, the principal financial effect of improving health in youth and middle age may be to increase the elderly population, and of course death can only be postponed, not eliminated. But I am painting with too broad a brush; careful study is required to assess the costs of lifestyle changes that might improve health.