Trends and correlates of class 3 obesity in the United States from 1990 through 2000.

Although the prevalence of obesity has markedly increased among US adults, health risks vary according to the severity of obesity. Persons with class 3 obesity (body mass index [BMI] > or = 40) are at greatest risk, but there is little information about this subgroup. To examine correlates of class 3 obesity and secular trends. Adults (aged > or = 18 years) in the United States who participated in the Behavioral Risk Factor Surveillance System telephone survey between 1990 (75,600 persons) and 2000 (164,250 persons). Body mass index calculated from self-reported weight and height. The prevalence of class 3 obesity increased from 0.78% (1990) to 2.2% (2000). In 2000, class 3 obesity was highest among black women (6.0%), persons who had not completed high school (3.4%), and persons who are short. During the 11-year period, the median BMI level increased by 1.2 units and the 95th percentile increased by 3.2 units. The prevalence of class 3 obesity is increasing rapidly among adults. Because these extreme BMI levels are associated with the most severe health complications, the incidence of various diseases will increase substantially in the future.