Trends in obesity and severe obesity prevalence in the United States from 1999 to 2018

Background: The national obesity epidemic and trend of obesity prevalence have been characterized by a series of cross-sectional surveys in the United States, however, less is known about obesity prevalence trajectory by birth cohort. This study aimed to investigate whether trends in obesity and severe obesity prevalence varied by birth cohorts among 1940s–1990s in the United States. Methods: Using data from the National Health and Nutrition Examination Survey 1999–2018. The trends of obesity and severe obesity prevalence were conducted with synthetic birth cohort. Results: There were 60 981 participants (weighted mean age, 38.1 years; female, 50.1%) assigned in 6 birth cohorts (1990s, 1980s, 1970s, 1960s, 1950s, and 1940s) over 1999–2018. The prevalence of obesity and severe obesity increased significantly with age during all birth cohorts except for the 1940s (P_trend <0.001). For obesity, a significant positive quadratic trend was observed among 1990s birth cohort (P_{non-linearity} = 0.037), while a significant positive linear trend (P_linearity <0.001) among 1980s, 1970s, 1960s, and 1950s birth cohorts. Corresponding to same weighted mean age, the prevalence of both obesity and severe obesity in younger birth cohorts were much higher than the older birth generations. Conclusions: The continued upward trend in obesity and severe obesity prevalence by birth cohort highlighted the need for continuing focus on surveillance of body mass index and identification, implementation, and evaluation of evidence-based interventions to address this major health problem in the United States.