BMI Doesn’t Work for All People

The body mass index is often used to predict risk factors and influence prescribed medical treatments. This became even more evident during the pandemic, when people with obesity and a high BMI were considered as having the same risk level as those with a suppressed immune system.

But did you know that the basis for the current BMI was developed nearly 200 years ago as the “Quetelet Index” by Belgian mathematician Lambert Adolphe Jacques Quetelet? He wanted to measure the height and weight of the “average” man based on a sample of white, European men.

The challenge for BMI’s use as a standard today is that it’s not adjusted for known differences in body composition and risk factors for people of color. For example, the World Health Organization released adjusted cut points for people of Asian descent, acknowledging that Asian people have different associations between BMI, percentage of body fat and health risks than those of European descent.

No such adjustments have been announced for Black or Hispanic people. Fatima Cody Stanford, MD, from Massachusetts General Hospital and Harvard University Medical School told the Washington Post that BMI cut points have roots in the Metropolitan Life Insurance Company’s attempt to establish how weight might play a role in someone’s likelihood of dying in the 1940s. The company created actuarial tables based on BMI and several decades of data from its clientele at the time, who were primarily white. Stakeholders blended this table with other government data and later coined the “body mass index” by physiologist Ancel Keys in 1972.

Stanford and other researchers propose an adjustment to the index to reflect currently known racial and ethnic variations in body composition from findings from the National Health and National Examination Survey between 1999 and 2016. Cut points for what constitutes “obese” for Black, white and Latino men would shift downward; cut points for Latinas and white women would be lower and the threshold for Black women would be higher.

The point is not merely theoretical. Physician use of BMI impacts clinical diagnoses and treatments, as well as psychological and financial outcomes for patients. Read the recommendations in Mayo Clinic Proceedings (2019; 94 [2], 362–63).

See also: BMI Proves Unreliable in Certain Populations