August 5, 2007 to August 12, 2007
Social Causes of Obesity
Social Causes of the Obesity "Epidemic"-Becker
Obesity is defined usually as a body-mass index of 30 or greater, where the body-mass index adjusts weight for height by dividing weight in kilograms by the square of height in meters. Obesity defined in any reasonable way has increased rapidly since 1980 in the United States, and to a lesser extent In Europe and Japan. About 30 per cent of all Americans have a body mass index of over 30, and about twice that number are considered to be merely overweight. While all economic levels, ages, racial groups, and both genders became heavier, obesity is much more common among the less educated, lower income persons, women, African-Americans, and Hispanics.
Several factors explain why the average weight of Americans (and those in other developed countries) increased a lot more rapidly after 1980 than it had before. The effective price of fatty foods began to decline rapidly at that time, in part due to the growth of fast food chains, like McDonald's. Also important, especially for teenagers, is the attraction of sedentary activities resulting from computers, email and instant messaging, and video games that replaced time at sports and other more physically challenging activities. (Television viewing by Americans did not increase, and may have declined, during the past 25 years.) The development of many drugs that combat high blood pressure, high cholesterol levels, and other ill health caused by being greatly overweight, and a reasonable expectation of further medical progress in the future, also contributed to the declining concern about being greatly overweight.
Social networks that influence eating and leisure activities has been recently suggested as a further factor in the spread of obesity. An article in the July 26 issue of The New England Journal of Medicine ("The Spread of Obesity in a Large Social Network Over 32 Years") analyzed the famous Framingham Heart Study for any evidence of social influences on obesity. This Study has followed about 5000 individuals and their children and grandchildren since 1948, with questionnaires on health, weight, friends, marital status, and many other variables. The recent exploration of these data between 1971-2003 for obesity social influences finds that a person becomes fatter when his or her friends, spouse, or siblings become fatter. The authors are aware that this does not necessarily mean causation from weight gain by friends and family to weight gain by this person. They probe further by adjusting for past weight, by looking at the timing of weight increases, by seeing if weight changes of neighbors are correlated (they are not), and develop a few other tests.
The results withstand all these tests, so they conclude that social influences of friends and family are important in the obesity "epidemic" of the past 25 years. Yet it is impossible with data of the kind in the Framingham Study to be sure that social influences rather than common changes in variables unobserved by the analyst explain why weight changes move together among friends or other social groups. To isolate the effects on behavior of group influences rather than the effects of changes in common forces, one needs evidence like what happened to their weights after college students are randomly assigned to each other as roommates (there is a study of the behavior of students who were so assigned), or evidence from other situations where one can more fully rule out friendships due to common interests and backgrounds. Still, it is plausible that eating habits and leisure and work activities are significantly influenced by what peers and family are doing. Indeed, considerable circumstantial evidence strongly suggests powerful social influences over many kinds of human behavior.
Nevertheless, however important is the impact of social influences on weight gains, they cannot explain why the trend toward obesity accelerated during the past several decades. For what social influences do is magnify, not start, the responses of groups to changes in prices, incomes, jobs, technologies available for games and communication, and other factors common to most members. For example, if a friend starts eating fast foods more frequently for whatever reasons, and I am influenced by his eating habits, then I would more frequently eat more fast foods as well. If he is also influenced by my eating habits, he eats even more of these foods than he did initially. But then I would eat still more as a result of his reaction to my eating. The end result could be a large increase in the fast food consumed by both of us, which could cause significant increases in our weights.
In effect, there is a multiplier response to any initial weight gains due to the presence of social interactions. To illustrate this "social multiplier" on weight changes, assume that if each time my peers gain a pound of weight, I gain 0.6 of a pound because I alter my behavior to correspond to theirs. If I influence their behavior to the same extent, then the social multiplier would be 2.5=1/1-0.6, which is the infinite sum of the series of back and forth interactions on weight changes among these peers. This means that if each member of a group on their own would gain 10 pounds as a result of say a decline in the price of fat, than each would end up gaining much more, 25 pounds, because of the social interactions among them.
This example shows how a sizable social multiplier on weight would transform moderate gains in weight when individuals are considered in isolation into possible epidemics after accounting for the interactions among members of a social network. The social multiplier on weight gains can be utilized to make it easier to lose weight. Individuals unhappy with being overweight can recognize that their chances of losing weight are greater if they acquire friends who are thin or who want to lose weight too. They could try to find such friends by attending exercise classes, or by joining online and other weight losing groups.
A company may want employees to lose weight in order to reduce absenteeism, and to save money on employee health insurance. It would be able to utilize the fact that employees' beliefs about their appropriate weights are influenced by how heavy their fellow employees are, especially when employees of the same firm are also friends. The company could heavily subsidize healthy meals, or offer bonuses to employees who lose weight, recognizing that these benefits might cause big reductions in weight because of the social multiplier.
Governments may try to reduce the incidence of obesity because of paternalism, or a desire to reduce public spending on ill health (I am skeptical about the value of such policies-see my blog post on October 8, 2006). It could take advantage of the social multiplier on weight by recognizing that even modest taxes on the fat in food or on fast food outlets would have large effects on the consumption of fat, and indirectly on weight loss, because of the social multiplier in eating patterns among friends, family, and others.
Social Obesity--Posner's Comment
In a heterogeneous society, practice tends to be normative. That is why homosexual activists greatly exaggerate the prevalence of homosexuality--asserting, on the basis of a misreading of Kinsey's famous studies, that 10 percent of the population is homosexual, whereas the true figure is probably at most 2 percent. The more homosexuals there are, the stronger their claim to be normal, a claim that would fail in a society that had a strict moral code condemning homosexuality.
Similarly, the more fat people there are, the more being fat is seen as normal. A half century ago, when obesity and overweight were relatively rare in this country, fat people were regularly ridiculed by entertainers, and this ridicule helped to keep people thin. As more and more people become fat, fatness becomes more normal-seeming, and the ridicule ceases (though another factor is the march of "political correctness," which discourages criticism of people's weaknesses).
It makes sense, as the recent article in the New England Journal of Medicine finds, that friends' fatness would have an influence distinct from that of the culture as a whole. We each inhabit a subcommunity or subcommunities within the national (and world) community as a whole, and we are more likely to take our clues from these subgroups than from the broader community. In my own ingroup of 16 judges (11 active members of my court, 4 senior members, and 1 nominee, who will replace an active member who will be taking senior status), only 2 are overweight (12.5 percent), compared to a nationwide average of 66 percent. Among my other friends, judicial and otherwise, the percentage who are overweight is probably no greater than 12.5 percent.
But separating out common causes from social influence is difficult. My social network consists almost entirely of affluent, educated people who are knowledgeable about calories and about the health effects of overweight, who can easily afford both expensive alternatives to junk food and membership in health clubs or ownership of exercise equipment, and who (this of course is related to their affluence and education) have a low discount rate and thus do not neglect long-term consequences of current behavior. One expects these people to be thin even if they are uninfluenced by the weight of the other people in their network. And likewise at the other extreme, with networks composed of people who are poor and badly educated and have high discount rates, all of which are correlated with obesity.
Still, it is plausible that there would be some social influence within these networks. The reason is that there is no clear notion of an optimal weight. Nobody bothers to compute his body mass, which requires translating one's weight from pounds to kilograms and then dividing by the square of one's height in meters (the normal range for the body mass index so computed is 18 to 24), simple as this computation is. A 2006 survey by the Pew Research Center finds that while people are acutely aware of the weight problem, they tend to regard themselves as of normal weight even when they are overweight, and this tendency to self-deception can be expected to be greater the heavier the people they associate with are. If you weigh 180 pounds, though you should weigh only 150, but your friends weigh 200 pounds, you will tend to think of yourself as thin. As Becker explains through the concept of a social multiplier, when you weighed 150 pounds your thinness may have constrained your friends, but when you move up to 180 you exercise a lesser constraint.
The social multiplier effect can of course operate in either direction. Among young professional women, there is a cult of thinness that seems to illustrate the effect. But it would be difficult to initiate such a downward cycle among the currently overweight.
Overweight may also be related to a decline in social conformity. There is more variety in people's dress, hair length, etc., than there was fifty years ago. Maybe it has become easier to make judgments about people without relying on crude signals, such as physical appearance. Then the costs of a nonnormal appearance would fall, and this would help to explain the increase in overweight.
A further point has to do with sedentary life style. That is rightly regarded as a risk factor for obesity. But in addition, being sedentary reduces the cost of being obese, since the less active one is, the less one is impeded by being obese. Fatness tends to creep up on one, and the less costly it is, the less incentive one has to lose weight, which is difficult.
Response to Comments on Social Obesity--Posner
An excellent comment points out that obesity increases with urbanization and female employment outside the home, and therefore is global. It increases with urbanization because urban work tends to be less physically strenuous than rural, and with female employment because work outside the home increases the time cost of home-cooked meals and thus the demand for restaurant, fast food, and junk food fare, all of which tend to be fattening because the purveyors compete to provide food that is at once cheap, tasty, and filling. In these respects, professional food preparers probably outcompete home cooking on average.
Several of the comments criticize my introductory remarks about homosexuality. I said that "in a heterogeneous society, practice tends to be normative. That is why homosexual activists greatly exaggerate the prevalence of homosexuality--asserting, on the basis of a misreading of Kinsey's famous studies, that 10 percent of the population is homosexual, whereas the true figure is probably at most 2 percent. The more homosexuals there are, the stronger their claim to be normal, a claim that would fail in a society that had a strict moral code condemning homosexuality. Similarly, the more fat people there are, the more being fat is seen as normal." One comment predicts that I will offer "profuse apologies" for these remarks and particularly for having used the term "homosexual" rather than the politically correct "gay," and another ascribes my political incorrectness to my age. The word "homosexual" is not pejorative; nor has it yet been displaced by "gay"; until it is, I have no inclination to switch merely in order to make a political statement. I should however have made clear that (as one of the comments notes) in saying that only 2 percent of the population is homosexual, I did not mean to suggest that only 2 percent have had a homosexual experience. In my book Sex and Reason I point out that "opportunistic" homosexuality (homosexual acts by persons whose orientation is heterosexual) is common in situations in which persons of the other sex are not available as sexual partners, as in prisons and (traditionally) on naval vessels. Ancient Greek homosexuality was primarily opportunistic, and today we have the curious phenomenon of "LUGS"--lesbians until graduation.