Body mass index (BMI) cutoffs for obesity in people of Black or Asian descent should be redefined to lower levels than the current thresholds for Whites based on risk for type 2 diabetes, according to findings from the first BMI threshold study in these ethnic groups.
Presented at this year’s online European Congress on Obesity (ECO) meeting, and simultaneously published in The Lancet Diabetes & Endocrinology, the analysis determined BMI cutoffs for obesity based on the risk of developing type 2 diabetes in adults from various minority ethnic groups in England, equivalent to the BMI cutoff for obesity of 30 kg/m2 for Whites.
Specifically, the study suggests age and sex-adjusted BMI thresholds of 23.9 kg/m² for those of south Asian descent; 28.1 kg/m² for Black individuals overall (26 kg/m² for Black Caribbeans); 26.9 kg/m² for those of Chinese heritage; and 26.6 kg/m² for Arab populations.
“We need to refine the BMI thresholds for ethnic minorities to prevent people in these communities from slipping through the net and missing out on early diagnosis and prevention opportunities for type 2 diabetes,” said lead author Rishi Caleyachetty, MD, from the University of Warwick, UK.
The current obesity threshold of ≥ 30 kg/m², used by the World Health Organization (WHO) and UK National Institute for Health and Care Excellence (NICE), is based on the relationship between BMI and mortality in exclusively White populations from research conducted back in the mid-1990s. In 2004, the WHO (and NICE) changed the cutoff to 27 kg/m² for south Asian and Chinese populations, but this decision was based on data from east Asia only and did not include Indians, Pakistanis, Bangladeshi, Black African, Black Caribbean, or Arab populations.
Caleyachetty emphasized that “Large numbers of people of ethnically diverse backgrounds are missing out on blood tests for type 2 diabetes or referrals for weight management services because of outdated BMI thresholds for obesity in ethnic minority groups.”
In the United States, the American Diabetes Association (ADA) already has guidance that recognizes the altered risk in Asians and has lowered the BMI threshold for overweight to 23 kg/m2 for the population.
But currently there is no different recommendation for Blacks or other racial groups. Asked why, an ADA spokesperson said the situation with Asian Americans is unique. “In terms of a lower BMI, American Asians store more visceral or abdominal fat at lower BMIs and therefore have an increased risk of diabetes without the usual definitions of being overweight at a BMI > 25 kg/m2 [or of having] obesity at a BMI of > 30 kg/m2.”
An accompanying editorial welcomes the new analysis but notes: “These ethnicity-specific BMI cutoffs apply only to the risk of developing type 2 diabetes, and might not apply to other obesity-related comorbidities [such as] cardiovascular disease risk factors, cancer, or mortality.”
David E. Cummings, MD, of the UW Medicine Diabetes Institute, University of Washington, Seattle, and Francesco Rubino, MD, chair of metabolic and bariatric surgery, Kings College London, UK, also highlight that the proposed thresholds might be limited by geographic and environmental scope.
“Because diabetes and obesity are influenced by genetic and environmental determinants, BMI cutoffs for obesity related to diabetes risk among various ethnic groups living in England could reflect interactions between genetics and local environments. Hence, the BMI cutoffs identified in this study might not be extrapolatable to the same ethnic groups living in other countries,” they observe.
Analysis Includes Indian, Pakistani, Bangladeshi, and Nepali Populations
In the new analysis, 1,472,819 people aged 18 years or older registered with a GP practice in England were included. The spread of ethnicities was 1,333,816 White, 75,956 south Asian (Indian, Bangladeshi, Pakistani, or Nepali), 49,349 Black, 10,934 Chinese, and 2,764 Arab.
Data were drawn from electronic health records across primary care (Clinical Practice Research Datalink) and hospital care (Hospital Episode Statistics).
In total, 97,823 people were diagnosed with type 2 diabetes during a median follow-up of 6.5 years. Models were then used to determine whether adults from the different ethnic subgroups had an equivalent risk of type 2 diabetes at a lower BMI than the White European population.
Asked whether he thought type 2 diabetes was the optimum “measure” to define an obesity threshold to manage disease, Caleyachetty said that firstly, type 2 diabetes is the most specific obesity-related complication, and secondly, it is a serious, chronic condition that can lead to serious health complications.”
“Mortality [the basis for prior thresholds] isn’t a specific complication of obesity,” he observed. “However, there are of course lots of other obesity-related complications such as cardiovascular disease and cancer and so on, and we are due to publish on this too,” he added.
“In theory, these cutoffs shouldn’t really be limited to use in the management of type 2 diabetes because type 2 diabetes is also a major risk factor for cardiovascular disease and mortality. There’s a clear rationale to apply these [the thresholds] to other cardiometabolic conditions given it often precedes them.”
Roadmap to Refine BMI Thresholds for Minority Populations
NICE recently considered revising thresholds but noted more evidence is required.
“We did this work to provide such evidence, so it would seem logical that they might re-think this now,” Caleyachetty noted.
He would like to see a roadmap to refine the BMI thresholds for ethnic minority communities. “NICE sourced its current threshold from WHO so we are going to start conversations with the Department of Health and Social Care, and NICE here in the UK, and [at] WHO.”
Such a revision should ensure the provision of appropriate clinical surveillance for patients in ethnic populations, commensurate with their greater risk of type 2 diabetes. That would help to prevent the future onset, and therefore facilitate early and effective treatment, of type 2 diabetes, say Caleyachetty and coauthors.
And given the COVID-19 pandemic and rapid pace of health policy change, Caleyachetty believes now is a good time to seek change.
“The [UK] Prime Minister is talking about addressing obesity because we know that [those with] obesity [and] type 2 diabetes and people belonging to ethnic minorities were disproportionately affected by COVID-19, both in the UK and US,” he observed.
“We would hope that there might be more expeditious movement in redefining these new BMI thresholds in these ethnic groups. “Any new thresholds would need to be incorporated into recommendations so healthcare practitioners are fully aware of the lowered BMI thresholds for these groups,” he added.
Of note, adjustment for socioeconomic and smoking status did not alter the BMI cutoffs, Caleyachetty and colleagues stress.
In closing, the editorialists say the study “has important implications. The differences in diabetes risk-related BMI cutoffs for obesity across different ethnic groups…support the notion that strict BMI cutoffs should not be used as standalone criteria to define indications for obesity therapies, especially bariatric and metabolic surgery.”
Caleyachetty has reported no relevant financial relationships. Disclosures for the other authors are listed in the article.
ECO 2021. Poster EP4-02. May 10-13, 2021.
Lancet Diabetes Endocrinol. Published online May 11, 2021. Full text
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