Before 1972, measuring someone’s weight relative to their height wasn’t really considered. Then physiologist Dr. Ancel Keys suggested it as a way to estimate body fat, and the formula got the name the body mass index or BMI. Now it’s in every medical chart, a consideration for life insurance and so much more.
As the go-to screening tool for obesity, it’s often the deciding factor in fertility treatment, joint-replacement surgery and weight loss medication. However, the original formula isn’t correct for all people. It was only designed for some body types and didn’t account for the normal variations between people.
The American Medical Association (AMA) adopted a new policy on the index, noting “significant limitations associated with widespread use of BMI in clinical settings,” adding it “loses predictability when applied on the individual level.”
Dr. Shannon Aymes is an assistant professor of medicine focused on weight management at the UNC School of Medicine. She uses BMI, other measurements and long patient visits to learn about her patients’ medication situation before making a health plan.
“Obesity, like all disease, is complex and cannot be captured with a single measurement,” said Dr. Aymes. “There are people with elevated BMI who have no evidence of disease typically associated with higher weight such as hypertension, obstructive sleep apnea and [blood sugar concerns]. But there are some people with modestly elevated BMI who have metabolic disorders that are potentially responsive to weight loss.”
BMI doesn’t account for factors like people weighing more because of muscle. Women tend to have more body fat than men. Body composition differs between different races. It also doesn’t consider where a person’s fat is located. “If you carry a lot of fat in your abdomen and around your organs, or visceral fat, basically, that’s bad,” said Dr. Ethan Weiss, a preventive cardiologist at UC San Francisco. “If you carry fat in your hips and your legs, your thighs and your rear end, that’s actually not only not bad, it’s good.”
This new guideline doesn’t mean that BMI is meaningless. But, the AMA is saying it shouldn’t be the only factor allowing people access to certain treatments or services. Telling people they need a treatment based on one number — or denying them because of another — can be dangerous.
Some news articles have framed this as just part of the culture war. The original formula was based on European men. However, while that might be at the root of the problem, the actual issue is that BMI is just one measurement of health and has taken on an oversized role. The AMA says that BMI can still be helpful when used with other measurements, like a physical and other tests. The problem is thinking that one single number can give a doctor a complete picture of someone’s health.
BMI isn’t meaningless, but it’s not the only health factor that matters. Many people feel bad about themselves when told their BMI and classified as obese without having any other factors considered.
This suggestion comes years after many doctors have acknowledged that BMI is not the be-all-end-all number it’s sometimes treated as. But other doctors still treat people like their BMI score. Hopefully, this recommendation helps those doctors stuck in the past. If you have a doctor who makes suggestions based on your BMI, bring this up in your next appointment. Ask about your other risk factors.
