Defining obesity is complex, because it depends on who you are

Obesity now affects 2 in 5 U.S. adults, making it one of the most important public health problems facing society. However, finding an accurate way to identify obesity in individuals remains challenging given the very diverse U.S. patient population.

In two new papers published in Annals of Internal Medicine, social justice and obesity experts weigh in on the Body Mass Index and discuss its advantages and challenges as a measure of obesity, particularly in different racial and ethnic groups, and how this influences perceptions and patient care.

Authors from New York University School of Global Public Health suggest that BMI (weight in kilograms divided by the square height in meters) remains useful for identifying obesity. While clinical decisions can be enhanced with additional measures, such as waist circumference and weight changes over time, BMI is strongly associated with indicators of cardiovascular risk, is low cost, and easy to measure in the clinical encounter.

And among healthy persons who do not smoke, studies also show that the relationship between BMI and mortality is nearly identical among Black persons, White persons, and Asian Americans in relative terms—and because BMI data are readily available across populations and time, it provides a useful metric by which to comprehend and quantify the ramifications of structural racism and discrimination for population health.

This enables researchers to gain deeper insights into the influence of systemic factors—including inequities in resource allocation, educational access, housing security, dietary options, and health care quality—on health outcomes and to develop efficacious interventions to mitigate health disparities.

Authors from Harvard Medical School, Massachusetts General Hospital, MGH Weight Center suggest, however, the implications of universal thresholds to define obesity may result in health disparities as obesity manifests differently in different populations.

The need for different BMI thresholds to define obesity in Asian populations offers lessons that may help to address existing disparities in health care. In 2004, the World Health Organization (WHO) suggested a lower BMI cutoff for many Asian populations because of their higher tendency toward central adiposity and risk for type 2 diabetes.

While these changes were clinically important, Asian populations are not monolithic and organizations should acknowledge these BMI thresholds as only temporary placeholders until we can establish whether even more specific thresholds are needed to define obesity across different Asian ethnic subpopulations. Authors advocate for more funding to research how to replace proxy values with better evidence-based thresholds.

The authors say that with recent pushes toward disaggregated data and personalized medicine, increasing granularity for Asian Americans could potentially pave the way for similar efforts among all racial and ethnic groups, making diagnosis of obesity more accurate, tailored, and equitable.

An accompanying editorial from Annals of Internal Medicine notes that consensus on how obesity should be defined remains elusive and argues that beyond diagnostic challenges, focusing on obesity exclusively as a disease rather than a broader, more inclusive construct may have unintended consequences—including reinforcing the weight bias in our current health care reimbursement system.

The health care community takes treating similar health risk factors including hypertension and high cholesterol seriously even before these result in disease complications, but health insurers, including Medicare, apply a higher bar when it comes to covering obesity treatment. Because obesity has multiple genetic, social, cultural, environmental and behavioral contributors, addressing obesity requires that clinicians have the time and space to get to know their patients as people. This is particularly imperative now for many reasons, including because of the increasing demand for new highly effective weight loss agents.

Equitable dissemination of these treatments will require clinicians to be able to make nuanced clinical decisions based on contributors to an individual patient’s obesity and the health risk it poses, and not just whether it meets a panel’s definition of “disease.” The author suggests that obesity should be recognized as a serious health threat and “pandemic,” and as such, clinical education about obesity needs to be a priority in medical school and residency training.