I have a personal stake in the answer to this question. For most of my adult life, my body mass index (BMI) has ranged between 22 and 25 kg/m2, which is considered to be in the normal range (the threshold for overweight is a BMI of 25, and obesity a BMI of 30). But it turns out that I've been overweight for most of that time if one applies a race-specific definition of overweight (BMI greater than 23) for individuals of Asian descent. Where did this race-based cutpoint come from, and is it still relevant in an era when we generally frown on using race as a surrogate for social determinants of health in making clinical decisions?
The story starts more than two decades years ago, when an expert committee convened by the World Health Organization (WHO) examined associations between BMI, body fat percentage, and risk factors for type 2 diabetes and cardiovascular disease in studies of Asian populations. They found that at similar BMI levels, Asian adults have higher body fat percentages and more metabolic risk factors than White adults. Although the WHO declined to formally establish different BMI thresholds for overweight and obesity in Asian populations, it suggested "additional trigger points for public health action": BMI greater than 23 represents "increased risk" and BMI greater than 27.5 represents "high risk."
In 2015, the American Diabetes Association (ADA) examined evidence from 4 cohort studies in Asian American populations and concluded that Asian American adults should be considered for diabetes screening if they have a BMI greater than 23, based on the prevalence of type 2 diabetes in this population being roughly equivalent to that in White Americans with a BMI greater than 25. (The U.S. Preventive Services Task Force recommends screening for prediabetes and diabetes in nonpregnant adults aged 35 to 70 with a BMI of 25 or greater, but it alludes to the ADA's lower threshold for Asian Americans in its practice considerations.) Notably, the studies cited by the ADA included virtually no persons of Chinese descent, despite Chinese being the largest Asian American subgroup. So this guideline does not necessarily apply to me.
However, a 2009 study of a large cohort (n=36,386) of Taiwanese civil servants and schoolteachers over age 40 found that all-cause mortality increased significantly at BMIs greater than 25, analogous to the increase in mortality seen in White populations with obesity (BMI > 30). Taiwanese adults with BMIs from 23 to 24.9 had no difference in all-cause mortality compared to persons with lower BMIs but showed a nonsignificant trend toward increased cardiovascular mortality that was not modified by smoking status. That this study suggested a nearly identical risk threshold as studies in other Asian American populations would argue that I am not exempt.
A more recent comparative study of minority populations living in England found that South Asians with lower BMIs had the highest risk of developing diabetes, followed by Arab, Chinese, Black, and finally White populations. Presumably, race and ethnicity were self-identified. Similarly, a 2023 scientific statement from the American Heart Association found that the risk of coronary artery disease appears to be highest among South Asian and Filipino Americans and lowest among Chinese, Japanese, and Korean Americans, but cautioned that limited disaggregated data precluded making clinical recommendations based on race or ethnicity. As a JAMA news article recently noted, the common practice of national surveys lumping diverse ethnic groups into a single "Asian" obscures disparities within those groups and frustrates efforts to achieve health equity.
My admittedly selective review of the data leads me to believe there is probably some value to considering more intensive lifestyle counseling and metabolic screening in Asian patients with BMIs between 23 and 25, like me. But what do we do about the rising numbers of American adults of mixed race? Perhaps "precision medicine" will eventually find a way to integrate genetic and environmental risks and let clinicians dispense entirely with numeric thresholds and race categories, but I would be surprised if this occurs before the end of my career in medicine.
