Obesity: BMI is the most common measurement, but it has flaws

The most common way to determine whether a person is obese is a simple calculation called the body mass index measurement.

BMI is determined by taking a person’s weight in kilograms and dividing it by height in meters squared. If the number is higher than 30, then the person is considered obese.

The American Academy of Pediatrics recommends an annual BMI screening for children and adolescents 2 years and older as part of routine care.

But BMI is not a perfect measure of whether someone is fat, according to the Centers for Disease Control and Prevention.

The CDC says BMI is correlated with direct measures of adiposity (body fatness), but it is not a direct measure.

BMI does not distinguish between fat and lean body mass, nor does it capture the body’s fat distribution or bone density. It is only used as a tool. People who have higher muscle mass may exceed the BMI standard for obesity but be in good physical condition.

The American Medical Association reported in 2023 that BMI has been an inaccurate measure across race, ethnic groups, sexes, genders and age spans.

The AMA now suggests BMI be used in conjunction with other physical measures such as visceral fat, body adiposity index, body composition, relative fat mass, waist circumference and genetic/metabolic factors.

“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. said in a news release about the issue in 2023. “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.”