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Abstract
Obesity prevalence has increased dramatically since the 1950s. While cross-sectional comparisons across racial, ethnic, and socioeconomic groups are abundant, there is less work on long-term trends. We assessed trends in average adult body mass index (BMI) in the United States by income, education, and racial/ethnic groups from 1959 to 2018 using the National Health and Nutrition Examination Survey, which assesses repeated cross-sectional, representative samples of the United States population. Height, weight, income, education, and race variables were extracted from raw data files; income data was converted to constant dollars prior to analysis. BMI was calculated from height and weight measurements. Interrupted time series analysis was used to compare trendlines for each decile of household income, education levels, and racial/ethnic groups. SAS version 9.4 was used for all analyses and figures were plotted using OriginPro 2021. Average BMI increased in all groups over the sixty-year period examined and all slopes were positive. BMI trends did not differ by income group or between high school graduates and greater than high school graduates. Less than high school graduates had a slower increase (smaller slope) in BMI compared to greater than high school graduates. Compared to non-Hispanic White participants, Black participants had higher slopes, while Hispanic and other racial groups had slower increases. Interactions among these subgroups also contained a mix of significantly different and statistically similar BMI trends. In summary, disparities in BMI are relatively constant across income categories and education level for high school graduates, though not constant among those with less than high school education, while trends are different among racial groups. These ongoing trends suggest that interventions to effectively address the obesity epidemic should focus on systemic change
