Increases in obesity in the United States are not simply a result of an across-the-board population weight increase. Rather, distributions of BMI in American adults over time are characterized by a gradual shift toward higher mean BMI, but with a marked increase in the higher end of the distribution, indicating that the largest increases have occurred in the highest weight categories.4, 7 The increase in mean BMI may be due to changes in environmental factors that influence all individuals, such as greater availability of high-calorie foods.8, 9 However, the increased number of people in the rightward tail of the BMI distribution suggests that there are subgroups of individuals who are particularly vulnerable to such a changing environment.
