Study highlights the need for more personalized approach to measuring BMI

The results of an extensive new study funded by the National Institute for Health Research (NIHR), Ethnic-specific BMI cut-off points for obesity based on type 2 diabetes mellitus risk: a cohort study of 1.5 million people in England, presented at this year’s European Congress on Obesity (ECO) and published simultaneously in the leading journal, The Lancet Diabetes & Endocrinology reveal that inaccurate and outdated interpretations of the standard Body Mass Index (BMI) values for patients from BAME backgrounds in England could potentially be putting their health at risk.

Researchers from four leading institutions [the University of Warwick, the University of Oxford, The London School of Hygiene & Tropical Medicine and UCL Institute of Health Informatics] came together in partnership with the Ethnic Health Forum to publish the pioneering study, analyzing data from over 1 million BAME people from England using both GP and hospital records. The study consisted of individuals aged 18 years and older and registered with a UK general practice between 1990 and 2018. 1,472,819 people with complete BMI and ethnicity data with at least one year follow up (1,333,816 White, 75,956 South Asian, 49,349 Black, 10,934 Chinese, 2,764 Arab) were included in the analysis. They used statistical models to confirm whether adults from BAME groups had an equivalent risk of type 2 diabetes at a lower BMI than the White European population.

For the equivalent age and sex adjusted incidence rate of type 2 diabetes at a BMI of 30 Kgm^-2 in White populations, the BAME BMI cut-offs were much lower: for South Asians, 23.9; Chinese, 26.9; Black, 28.1; and Arab 26.6. The study therefore conclusively shows for the first time that people from BAME backgrounds are more likely to develop type 2 diabetes at much lower BMIs than people from White ethnic backgrounds.

BMI uses height and weight to work out if a person’s weight is healthy (weight / height x height) and according to current NHS guidelines, an adult with a BMI of 30 Kgm^-2 or above is obese.

However, this figure is traditionally based on the increased mortality risk for adults from White ethnic groups. Importantly, this new study has established that compared with the risk for development of type 2 diabetes at BMI 30 Kgm^-2 in White people, the equivalent risk amongst BAME people occurred at much lower cut-offs than the current NHS recommended ethnic-specific BMI cut-offs.

In light of this new evidence, the research team recommends that it is now vital – more so than ever, given the increased focus on health inequalities affecting millions of people from BAME backgrounds as well as the link between obesity and COVID-19 (a condition also adversely affecting UK BAME people) to change BMI values than are currently used to trigger action to prevent type 2 diabetes among people from BAME backgrounds. As illustrated below, new obesity cut-offs developed during the study further emphasize how ‘one size does not fit all’ when it comes to BMI.

The revised figures in the South Asian ethnic group are substantially lower than the current NHS recommended “cut-off” BMI of 27.5 Kgm^-2, used to trigger action to prevent type 2 diabetes. This means that healthcare professionals may miss the opportunity to identify those at risk as well as a subsequent referral to vital weight management services, blood tests and screening for obesity-related co-morbidities such as type 2 diabetes.

The study’s Principal Investigator Dr Rishi Caleyachetty (Junior Doctor and Epidemiologist, University of Warwick), comments; “As a doctor, I’m extremely concerned that if the current BMI values are not amended to account for ethnicity, many BAME people will needlessly slip through the net, leaving them unknowingly at risk of type 2 diabetes.

“I meet people from BAME backgrounds who tell me about the lack of information on what a healthy weight is for their community. Another person, who had been told they were at high risk of developing type 2 diabetes told me he was surprised because he was not “fat”. These are just two examples from many cases, indicating that a ‘blanket’ set of BMI values could be disadvantaging BAME people from accessing services to prevent type 2 diabetes.”

A co-investigator on the study, Dr Thomas M Barber (Associate Professor and Honorary Consultant Endocrinologist at the University of Warwick and University Hospitals Coventry and Warwickshire [UHCW]), Clinical Lead of the Obesity service at UHCW comments; ‘’These data are very important and should inform future clinical guidance and policy regarding the management of obesity in BAME people. Our data also promote an individualized approach to the effective screening and management of obesity-related conditions (such as Type 2 Diabetes Mellitus) in BAME people.

In the wake of these new findings, the research team hopes that GPs and other healthcare professionals will feel encouraged to use these ethnic-specific BMI cut-offs to trigger action to prevent type 2 diabetes in England.

Furthermore, with these new cut-offs allowing for a more personalized approach to BMI, GPs and primary care practitioners should also feel more confident about having well-informed, positive conversations with their patients about weight management. Obesity should not be a ‘taboo’ subject, particularly given the risks associated with being obese in the current health climate.

An important outcome of this study is that BAME people from England will have a better, more personalized understanding of BMI cut-offs. Furthermore, the findings will help raise awareness within these groups of the increased risk of type 2 diabetes at much lower BMI values than previously recognized.

Critically, the research teams are now working closely with key organizations to share the findings with Department of Health & Social Care policy makers, NHS professionals and BAME people in England.

A co-investigator on the study, Dr Paramjit Gill (Professor of General Practice, GP, and Head of the Division of Health Sciences at Warwick Medical School at the University of Warwick), comments; “This work highlights that we need evidence for all ethnic groups as they are at risk of diabetes at different levels of BMI. A blanket approach is not acceptable any longer.”

This far-reaching, extensive study has shed light on a worrying generalization of BMI cut-offs for obesity, which comes at the expense of those from a range of ethnic backgrounds. A complete revision of ethnic-specific BMI cut-offs to trigger action to prevent type 2 diabetes is needed. This will ensure healthcare professionals provide appropriate recommendations for BAME patients regarding lifestyle changes, referrals to weight management services and investigations for type 2 diabetes.

Dr Rishi Caleyachetty, Study’s Principal Investigator

He adds; “We hope that this study will swiftly kickstart a review of current BMI policy in the UK for BAME people, in order to prevent both type 2 diabetes, and facilitate early and effective treatment of type 2 diabetes. We all know the NHS was founded on the principles of fairness and that all patients regardless of their background should be cared for equally. But it is clear at the moment these principles may not be a reality for many BAME people.”