Secular trends in body mass in the United States, 1960-1980

Data from four National Health Examination Surveys conducted of the US population from 1960 to 1980 were analyzed to determine secular trends in obesity for white and for black adolescents and young adults of both sexes. Body mass index was categorized into four levels using cut points determined by the 50th, 75th, and 85th percentiles at the first survey in 1960-1962. The weighted proportions of persons in these body mass categories were determined, and statistical models were developed to describe secular trend and race effects. No consistent secular trends were found for white or black youths aged 12-17 years. No significant secular trends in obesity were found for white or black young males aged 18-34 years. Both for white and for black adult females, there were significant secular increases in the proportion of adult females in each of the successively heavier categories of body mass index. These increases were identical for white and for black adult females on the log-odds scale, but black adult females were already significantly heavier at the first survey. This race effect persisted throughout the entire time interval.