By Saadia Aslam
A study by Caleyachetty et al has prospectively identified ethnicity-specific BMI cutoffs for obesity based on the risk of type 2 diabetes that are risk-equivalent to the BMI cutoff for obesity among White populations (≥30 kg/m2).
Research in context: (directly taken from the paper)
Evidence before this study
WHO and the National Institute for Health and Care Excellence (NICE) in England both recommend a BMI cutoff of 27·5 kg/m2 to trigger action to reduce the risk of obesity-related conditions, such as type 2 diabetes, in south Asian and Chinese populations. This recommendation is based on a sparse evidence base and therefore might be inappropriate for some minority ethnic groups. Previous studies have attempted to identify BMI cutoffs for obesity in multi-ethnic populations by use of data on type 2 diabetes prevalence or a surrogate marker, small sample sizes, and self-reported disease status, including relatively few minority ethnic groups. Because type 2 diabetes can be delayed or prevented through dietary change, physical activity, and the early use of antihyperglycaemic therapy, it is important to establish BMI cutoffs for obesity in relation to the risk of type 2 diabetes among adults from minority ethnic populations in England that equate to those developed in White populations.
Added value of this study
In a comprehensive analysis, we define BMI cutoffs for obesity based on the risk of developing type 2 diabetes in minority ethnic adults equivalent to the BMI cutoff for obesity of 30·0 kg/m2 set for White populations. To our knowledge, this study is the first to provide BMI cutoffs for obesity for Arab populations and Black and south Asian ethnic subgroups. We also highlight the value of routine electronic health records and the use of large, linked datasets to provide precise ethnicity-specific BMI cutoffs for obesity. In our study, we included 1 472 819 people aged 18 years or older registered with a general practitioner practice in England at any point between 1990 and 2018 (1 333 816 were White, 75 956 were south Asian, 49 349 were Black, 10 934 were Chinese, and 2764 were Arab). For an equivalent age-adjusted and sex-adjusted incidence of type 2 diabetes at a BMI of 30·0 kg/m2 in White populations, we found lower BMI cutoffs for south Asian (23·9 kg/m2), Black (28·1 kg/m2), Chinese (26·9 kg/m2), and Arab (26·6 kg/m2) populations.
Implications of all the available evidence
By contrast to WHO expert consultation recommendations and NICE guidelines, our study shows that Black Caribbean, south Asian, Chinese, and Arab populations living in England had an equivalent risk of type 2 diabetes at substantially lower BMI values than the current BMI cutoffs for obesity. Our findings should guide revisions of current ethnicity-specific BMI cutoffs to trigger action to reduce the risk of developing type 2 diabetes and equalise opportunities for the increased prevention and early diagnosis of type 2 diabetes.
Reference: Caleyachetty R, Barber TM, Mohammed NI, Cappuccio F, Hardy R, Mathur R, Banerjee A, Gill P. Ethnicity-specific BMI cutoffs for obesity based on type 2 diabetes risk in England: a population-based cohort study. Lancet Diabetes & Endocrinology. Published online: 11th May 2021 https://doi.org/10.1016/ S2213-8587(21)00088-7