Sex differences in the secular change in waist circumference relative to BMI in five countries from 1997 to 2020

Objective: The objective of this study was to quantify changes over time in waist circumference (WC) relative to BMI by sex in the Americas (United States, Mexico, Chile, and Peru) and England. Methods: Data from adults aged 25 to 64 years between 1997 and 2020 were analyzed, and US data were stratified by race and ethnicity groups. Sex-specific BMI and WC means and obesity and abdominal obesity prevalence were compared between the first and last surveys. Using data from all survey years, secular changes across the BMI and WC distributions were estimated, applying quantile regression models. BMI was added as a predictor of WC to estimate secular changes in WC relative to BMI. Interaction terms were included in all models to evaluate differences by sex. Results: BMI and WC (except for Peru) showed larger secular increases at the upper- tails of the distributions in both sexes. Increases at the 50th and 75th WC percentiles relative to BMI were more pronounced in women than in men, with larger increases in US non-Hispanic White individuals and in England. In men, increases in WC independent of BMI were most evident in Mexico. Conclusions: Disease risk associated with visceral fat is potentially underestimated by national surveillance efforts that quantify only secular changes in BMI.