Here's Why Doctors Should Avoid Relying on BMI: A New Statement from AMA

The American Medical Association (AMA) is urging healthcare professionals to shift away from body mass index (BMI) as a critical health measurement.

In a new report on public health problems in the US, the organization said the BMI classification system is “misleading” and stressed the importance of developing other ways to monitor people’s health.

For years, a key tool BMI used to estimate disease risk, Priya Jaisinghani, MD, an obesity medicine specialist at NYU Langone, told Health.

Because of this, insurance companies have been able to deny coverage of some medical treatments to people with certain BMI measurements.

A press release on the AMA’s report said that moving forward, insurers shouldn’t place such a heavy emphasis on BMI measurements. “The AMA also recognizes that…BMI should not be used as a sole criterion to deny appropriate insurance reimbursement,” the press release said.

The new report also noted that the flawed classification system has been particularly harmful to some communities of color.

The BMI measurement was established from data on white populations, but experts historically assumed BMI measurements had the same implications for everyone regardless of race or ethnicity—which isn’t the case Marcio Griebeler, MD, director of the Obesity Center at Cleveland Clinic’s Endocrinology and Metabolism Institute, told Health.

“The same BMI in [some minority populations] can mean a completely different thing when you compare it to the white population,” he said. “That’s a big, big limitation of BMI.”

A person’s BMI is their weight in pounds divided by the square of their height in meters. BMI measurements fall into one of the following four categories:

• Underweight: less than 18.5
• Normal weight: 18.5 to 24.9
• Overweight: 25 to 29.9
• Obese: 30 or greater

The measurements are simple, which is one of the reasons BMI became such a popular wellness indicator. “It’s easy, since we just have to have height and weight,” Griebeler said. “We’ve used it a lot because it’s convenient. But it’s far from perfect.”

He explained that, without the proper context, BMI measurements don’t provide helpful information for patients or doctors. This is because BMI measurements don’t take into consideration what percentage of a person’s total body weight is fat.

For example, Griebeler said he recently had two patients working on weight management. One lost weight and saw their BMI decrease. The other did not see a dip in their BMI, despite taking weight loss precautions, including regular exercise. But the latter patient had actually lost more fat than the former. The reason their BMI didn’t change was because they had gained muscle. This is one example of how the same BMI can mean many different things in different patients.

“You cannot compare people,” Griebeler said. “It’s very complicated.”

For this reason, medical decisions such as who qualifies for bariatric surgery or weight loss medications shouldn’t be based on BMI alone, nor should insurance reimbursement policies.

“People use BMI to make decisions, but we need to understand the limitations,” Griebeler said. “In the obesity field, we’re trying to go beyond the BMI, because now we understand” it doesn’t always provide an accurate assessment of a person’s health.

The BMI scale was developed to measure white people. Therefore, we can’t assume it can measure all people accurately, Jaisinghani said. “BMI does not account for ethnic variations of obesity.'

For instance, the new report explains that Asian people have more body fat than white people. “A lower BMI in the Asian population can mean obesity, even though that BMI would not [signify] obesity in the white population,” Griebeler said.

Previous research has found that non-Hispanic Black people tend to have less body fat than their white counterparts. If two populations’ BMI measurements were compared, some Black people may be inaccurately characterized as “unhealthy” due to a high BMI, even though their BMI could be due to high muscle mass and not high body fat.

In addition to race and ethnicity, a person’s body shape, age, sex, and gender influence their BMI. The press release emphasized that these nuances should always be factored into discussions on weight management.

Weight management is personal. It’s important to speak with a healthcare provider if you don’t know whether or not losing weight could improve your health.

Calculating your BMI won’t give you enough information about what the best path is for you, Griebeler said. He noted that looking at BMI out of context can be confusing and unclear.

Another measurement that might be checked in a doctor’s office—and that you can also keep track of at home—is waist circumference. Taking this measurement can be a helpful way to track your size over time, and it’s accessible to anyone who owns a measuring tape.

“It’s very easy, and it’s not expensive,” Griebeler said. According to Jaisinghani, your doctor can also help you determine your waist-to-hip ratio and skinfold thickness, which can be helpful for patients looking into weight management techniques.

Physicians may use more advanced methods to determine whether you could benefit from losing weight.

Among these, Griebeler said, is a device called a body composition machine. “With these, you can check water content, fat content, and skeletal muscle mass,” he said.

While the new report urges physicians to take a step back from BMI, Griebeler explained that it doesn't imply banning BMI from weight management discussions.

“We should still be using it,” he said, because it’s accessible to everyone. The key, he added, is using BMI in conjunction with other measurements to get a fuller picture of someone’s overall well-being.

Experts said the new AMA report is significant because it has the potential to help patients make science-based decisions about their health. “With the new AMA policy,” Dr. Jaisinghani said, “hopefully this will be the start of [being] more inclusive of differences across different ages, sexes, genders, and ethnicities.”