Social Dynamics of Obesity


Consistent with data from two large surveys of body weights of the United States population covering the period from 1976 to 2002, researchers Mary A. Burke and Frank Heiland predict increases in average weight and substantial growth in the upper tail of the distribution. This occurs as falling food prices influence individual behavior as well as the endogenous weight norm, setting off a multiplier effect. Relative to earlier models pointing to the role of food prices in the obesity epidemic, we predict larger net effects of price on weight, where the price elasticity should be greater in the long run than in the short run. While previous models have made qualitative predictions of rising obesity rates, they have not captured the specific changes in the distribution reproduced in the Burke/Heiland model.


Alarming statistics on the growth of obesity in the United States (and, more recently, in other countries as well) have been widely publicized in recent years. Obesity has become the object of grave concern among public health officials, and has spawned voluminous research in the fields of medicine and public health. Concern has focused on understanding obesity medically, as well as on the cost of obesityrelated morbidity and mortality, in both economic and human terms (Hassan et al. 2003; Himes 2000; Hamermesh and Biddle 1994; Cawley 2004; Pagan and Davila 1997). The level of alarm has become so pronounced as to have already spawned a backlash.1 While average weights increased steadily, suggesting a rightward shift of the weight distribution, perhaps the most dramatic development is the growth in the upper tail. Among women, for example, the 95th (99th) percentile weight moved from 215 (258) pounds in 1976-80 (NHANES II) to 251 (305) pounds in 1999-2000 (NHANES 99), while over the same period average weight increased from 148 to 168 pounds, as shown in Table .2,3 The official definition of obesity employed by the Centers for Disease Control (CDC) and by the World Health Organization (WHO) is a body mass index (BMI) value of 30 or greater, where BMI is the ratio of weight, measured in kilograms, to squared height, measured in meters. For a woman 5’4″ tall, a weight of 175 pounds or greater classifies as obese, and for a man 5’9″ tall, the obesity weight threshold is 203 pounds.