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

CONTEXT: 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.

OBJECTIVE: To examine correlates of class 3 obesity and secular trends.

DESIGN, SETTING, AND PARTICIPANTS: 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).

MAIN OUTCOME MEASURE: Body mass index calculated from self-reported weight and height.

RESULTS: 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.

CONCLUSION: 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.