The use of the body mass index (BMI) by doctors is under scrutiny after the American Medical Association (AMA) laid out its historic harms — including racist exclusion — in a new report. 

The report, presented at the 2023 AMA House of Delegates meeting, found that BMI doesn’t provide accurate measurements for people of color. This is because the generations-old screening tool was created based on medical data from white people only

“It is important for physicians to understand the benefits and limitations of using BMI in clinical settings to determine the best care for their patients,” Jack Resneck, AMA’s immediate past president, said in a statement

The association adopted a new policy clarifying how BMI can be used in medicine moving forward.

BMI is a numeral scale used to determine a person’s weight category. To figure this out, physicians divide the individual’s weight by height. If under 18.5, the person is considered underweight. Anything over 30 is considered obese — a condition that reportedly impacts Black Americans more than others. 

According to the U.S. Department of Health and Human Services, four out of five Black women are considered overweight (a BMI between 25 and 29) or obese. 

Black children are also up to two times more likely than white kids to be considered obese, according to the Centers for Disease Control and Prevention (CDC).

Obesity is known to lead to other health issues, such as heart disease, stroke, and type 2 diabetes. 

BMI doesn’t account for body composition, the percentage of body weight that’s fat versus lean mass, such as muscle.

“There are numerous concerns with the way BMI has been used to measure body fat and diagnose obesity, yet some physicians find it to be a helpful measure in certain scenarios,” Resneck said.

The CDC says BMI is an “inexpensive” and “easy screening method weight category” but “does not measure body fat directly.” On the other hand, the AMA says the tool is “significantly correlated with the amount of fat mass in the general population but loses predictability when applied on the individual level.”

BMI doesn’t account for body composition, the percentage of body weight that’s fat versus lean mass, such as muscle. This means a person with high percentages of muscle mass can be inaccurately classified as obese, though their actual amount of body fat is normal. 

Previous research has found that Black women have more bone and muscle mass, but less fat, as a percentage of body weight, than white women, after controlling for ethnic differences in age, body weight, and height. 

“The AMA also recognizes that relative body shape and composition differences across race/ethnic groups, sexes, genders, and age-span is essential to consider when applying BMI as a measure of adiposity and that BMI should not be used as a sole criterion to deny appropriate insurance reimbursement,” AMA said. 

The association suggests that BMI be used in addition to other “valid” measures, such as “measurements of visceral fat, body adiposity index, body composition, relative fat mass, waist circumference, and genetic or metabolic factors.”

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