Amid the buzz around weight loss drugs and rising rates of obesity worldwide, many healthcare professionals are questioning the use of body mass index (BMI) as a measure of obesity. The American Medical Association (AMA) adopted a new policy, calling on doctors to deemphasize the role of BMI in clinical practice.

BMI is a measurement that divides body weight in kilograms by height in meters squared. It rose to prominence in the 1990s as the official screening index for obesity. However, there are major limitations to using BMI as a measure of health.

Research has shown that BMI at a population level correlates strongly with body fat percentage and risk for serious health conditions. However, BMI does not directly measure body fat for an individual. People with the same BMI may have substantially different body fat percentages based on factors such as age, muscle mass, sex, and race. BMI also cannot provide precise information about the distribution of body fat, which is important because fat stored around the internal organs has higher health risks.

Further, health outcomes associated with a specific BMI can vary based on factors such as race, sex, age, and physical fitness level. For example, some studies suggest that BMI in the overweight to class 1 obesity range does not raise the risk of early death.

The AMA recommends alternative measures for assessing the health risks of an elevated body weight, such as body adiposity index, relative fat mass, waist-to-hip ratio, and waist circumference. These measures attempt to better characterize fat distribution in the body, but evidence for their use in improving health outcomes is lacking.

In conclusion, the AMA’s new policy marks a significant shift in how clinicians regard obesity and highlights the limitations of using BMI as a measure of health. Further research is needed to identify the best ways to assess the health risks of elevated body weight.