Comparison of race- and ethnicity-specific BMI cutoffs for categorizing obesity severity: a multicountry prospective cohort study

Objective: The objective of this study was to compare race- and ethnicity-specific BMI cutoffs for the three classes of obesity based on equivalent risk of type 2 diabetes (T2D). Methods: Participants without T2D were included from the UK Biobank, the China Health and Nutrition Survey, and the Singapore Chinese Health Study. Poisson regressions with restricted cubic splines were applied to determine BMI cutoffs for each non-White race and ethnicity for equivalent incidence rates of T2D at BMI values of 30.0, 35.0, and 40.0 kg/m² in White adults. Results: During a median follow-up of 13.8 years among 507,763 individuals, 5.2% developed T2D. In women, BMI cutoffs for an equivalent incidence rate of T2D as observed at 40.0 kg/m² in White adults were 31.6 kg/m² in Black, 29.2 kg/m² in British Chinese, 27.3 kg/m² in South Asian, 26.9 kg/m² in Native Chinese, and 25.1 kg/m² in Singapore Chinese adults. In men, the corresponding BMI cutoffs were 31.9 kg/m² in Black, 30.6 kg/m² in British Chinese, 29.0 kg/m² in South Asian, 29.6 kg/m² in Native Chinese, and 27.6 kg/m² in Singapore Chinese adults. The race and ethnicity order was consistent when equivalent BMI cutoffs were estimated for class I and II obesity. Conclusions: Establishing a race- and ethnicity-tailored classification of the three classes of obesity is urgently needed.