Body mass index has ‘significant limitations’ as measure of health, AMA says

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Body mass index (BMI) might not be the best way to measure patients’ size as it relates to health.

The American Medical Association (AMA) has adopted a new policy that aims to clarify how BMI is used as a measure in medicine. AMA announced its delegates approved the policy as part of the association’s annual meeting this week.

“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,” AMA Immediate Past President Jack Resneck Jr., MD, said in a news release. “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.”

BMI clinical use and history

The U.S. Centers for Disease Control and Prevention (CDC) defined BMI as a person’s weight in kilograms (or pounds) divided by the square of height in meters (or feet).

“A high BMI can indicate high body fatness,” according to CDC. “BMI screens for weight categories that may lead to health problems, but it does not diagnose the body fatness or health of an individual.”

AMA claimed there are “significant limitations associated with the widespread use of BMI in clinical settings.”

BMI correlates with the amount of fat mass in the general population, but loses predictability in individuals. Body mass index “does not account for differences across race/ethnic groups, sexes, genders, and age-span,” according to AMA, and the CDC acknowledges there are clinical limitations to consider about it.

There also are historical issues relating to BMI, which has been used “for racist exclusion, and because BMI is based primarily on data collected from previous generations of non-Hispanic white populations,” according to AMA.

Measure up

How to measure patient health based on body size and function?

Earlier this year, researchers at the Seattle, Washington-based Institute for Systems Biology (ISB) unveiled a new biological body mass index. Based on multi-omic profiling of blood, genetic risk scores, and gut microbiome composition, researched used machine learning models to generate the biological BMI.

The researchers said the findings suggest that with positive lifestyle changes, patients may be getting healthier, even if they are not losing weight.

“For years, BMI has been the go-to measure for doctors to classify individuals based on their height and weight in comparison to an average person. However, this average person doesn't truly exist,” corresponding author Noa Rappaport, PhD, said in a news release. Rappaport is a senior research scientist at ISB.

“We now have the capability to use advanced molecular measurements as a more comprehensive representation of a person's metabolic health, which can be used to make more accurate clinical recommendations for individuals,” Rappaport said.

Multiple paths to health

Regardless of how it’s measured, researchers earlier this year reported primary care physicians need a weight loss tool for patients because the doctors are not doing enough for weight management. They hope the new PATHWEIGH tool could become a new pragmatic approach for physicians to use with patients.

Prescription medications including the anti-obesity drug Wegovy and diabetes management drug Ozempic have received widespread public attention for patients losing weight.

But earlier this year, the American College of Lifestyle Medicine (ACLM) reminded physicians that those are not the only interventions. Earlier this year, the College published an official position statement that physicians who want their patients to get healthier by managing overweight and obesity, should start with “compassionate, evidence-based lifestyle interventions.”

With or without surgeries and medications, ACLM said patients’ best interests call for treatment of six lifestyle pillars:

• Regular physical activity
• Whole-food, plant-predominant nutrition
• Restorative sleep
• Stress management
• Positive social connection
• Avoidance of risky substances

“The more tools clinicians have available to treat patients who have overweight or obesity, the better,” ACLM President Beth Frates, MD, FACLM, said in a news release. Frates is a clinical Assistant Professor at Harvard Medical School.

“As ACLM’s position statement makes clear, it is vital that evidence-based lifestyle interventions always remain at the center of any comprehensive treatment plan, not only to treat people who are overweight or obese but also to treat many other preventable chronic diseases like heart disease and type 2 diabetes,” Frates said. “We here at ACLM stand ready to partner with organizations working to alleviate the burden of chronic conditions, and we have a plethora of resources to share.”