United States

Meltzer and Zhuo Chen Since 1970, the rate of obesity in the United States has increased from about 14 percent to over 25 percent and has come to be recognized as a major pub-lic health concern (NIH 1998; Flegal et al. 1998, 2005; Ogden et al. 2006). Understanding the causes of obesity is important because it may suggest strategies to address the increase in obesity. Increases in body weight are the result of an excess of caloric intake relative to caloric expenditure. Changes in both caloric expenditure and caloric intake have been hypothesized to have contributed to increasing obesity in the United States. Factors that have been suggested to have decreased caloric expenditure include the development of a more sedentary lifestyle due to the decreasing role of physical labor in work and the increasingly sedentary nature of leisure activities due to the growth of television and video games. Factors affecting food consumption that have been emphasized include the greater consumption of “fast- food” away from home and the declining cost of eating a diverse set of food