AMA Policy Recognizes History, Challenges With Using BMI in Medicine

The American Medical Association (AMA) recently adopted a policy regarding the use of body mass index (BMI) in medicine, recognizing its historical harms and acknowledging that it is based on limited data.¹

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The new policy was part of the AMA’s Council on Science and Public Health report, which evaluated the problematic history with BMI and possible alternatives. The delegates also noted that BMI is an imperfect way to measure body fat in many groups because it does not account for differences across racial or ethnic groups, sexes, genders, and ages. Given these issues, the new policy suggests the AMA educate physicians on these concerns and alternative measures for diagnosing obesity.¹

“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,” said AMA Immediate Past President Jack Resneck, Jr, MD, in a press 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.”¹

BMI uses a simple formula to determine whether individuals are overweight or underweight, with most health experts advising a BMI between 18.5 and 24.99. The formula was created in the 1830s by Lambert Adolphe Jacques Quetelet, an astronomer, mathematician, statistician, and sociologist, although it was not more widely used until the early 20th century. Quetelet introduced the concept of “social averages,” and attempted to use various formulas to determine the “normal” or “average” man.²

Although it is well established that increased amounts of fat around the abdomen can increase various health risks, BMI fails to account for differences in race, ethnicity, age, sex, and other factors. For example, although a BMI higher than 25 is typically considered unhealthy, experts have noted that a BMI of 23 or higher could be unhealthy for Asian individuals.²

Age is also an important factor, with the BMI measurement considered invalid in children and young adults under the age of 20. Instead, underweight and overweight children are categorized based on percentile charts. As individuals age, there is also a greater likelihood that their bones will become osteoporotic and less dense, although the BMI calculation does not account for this.²

Importantly, the history of BMI as a measure of health also has racist origins, with the AMA policy noting that it was used as a tool for racist exclusion.1 Black communities, and Black women in particular, have long been known to have higher rates of chronic cardiovascular, inflammatory, and metabolic risk factors, even after controlling for factors such as smoking, physical exercise, or diet.¹

Researchers have also noted that Black women are the subgroup with the highest BMI in the United States, and 4 out of 5 are classified as either overweight or obese. Physicians have long attributed poorer health outcomes among Black women to these higher BMIs, and Black women have been specifically targeted by campaigns urging them to “eat less and exercise more” to lose weight.¹

However, more recent research has found that social determinants of health, such as generational trauma, higher rates of poverty, and racially segregated neighborhoods have more significant impacts on health than BMI or health-related behaviors. For example, low-income Black neighborhoods are more often impacted by environmental toxins, air pollution, and lack of grocery stores with nutritious food choices, all of which influence rates of chronic mental and physical illnesses.³

Because of all of these various concerns, the AMA House of Delegates urged clinicians to consider relative body shape and composition heterogeneity across race and ethnic groups, sexes, genders, and ages when applying BMI as a measure of adiposity. Additionally, they said it should not be used as a sole criterion to deny insurance reimbursement.⁴

Delegates also modified the existing policy on the clinical utility of measuring BMI, with the goal of supporting “greater emphasis in physician educational programs on the risk differences within and between demographic groups at varying levels of adiposity, BMI, body composition, and waist circumference and the importance of monitoring these in all individuals.”⁴

“Numerous comorbidities, lifestyle issues, gender, ethnicities, medically significant familial-determined mortality effectors, duration of time one spends in certain BMI categories, and the expected accumulation of fat with aging are likely to significantly affect interpretation of BMI data, particularly in regard to morbidity and mortality rates,” the report says.⁴

References

1. AMA adopts new policy clarifying role of BMI as a measure in medicine. News release. American Medical Association. June 14, 2023. Accessed June 22, 2023. https://www.ama-assn.org/press-center/press-releases/ama-adopts-new-policy-clarifying-role-bmi-measure-medicine
2. Humphreys S. The unethical use of BMI in contemporary general practice. Br J Gen Pract. 2010;60(578):696-697. doi:10.3399/bjgp10X515548
3. Strings S, Bacon L. The Racist Roots of Fighting Obesity. Scientific American. June 4, 2020. Accessed June 22, 2023. https://www.scientificamerican.com/article/the-racist-roots-of-fighting-obesity2/
4. Berg S. AMA: Use of BMI alone is an imperfect clinical measure. American Medical Association. June 14, 2023. Accessed June 22, 2023. https://www.ama-assn.org/delivering-care/public-health/ama-use-bmi-alone-imperfect-clinical-measure