Why body mass index doesn’t give the whole health picture

The American Medical Association this week urged doctors to deemphasize their use of body mass index (BMI) in determining healthy weights for patients. The new guidance encouraged clinicians to employ other measures in conjunction with BMI, including waist circumference and body composition. 

“BMI is the simplest measure, beyond weight, to try to make an assessment of whether a specific individual’s weight is potentially posing some harm to them. But it is very limited in giving us that information,” said Dr. Scott Hagan, an assistant professor of medicine at the University of Washington School of Medicine. 

BMI is a calculation of a person's weight divided by the square of their height. The resulting figure describes someone as underweight (≤18.4), at a healthy weight (18.5-24.9), overweight (25.0-29.9) or obese (≥30). View a BMI chart. 

Hagan says BMI doesn’t provide patients or clinicians with a complete picture.  

“Elevated BMI, at least defined the way that the World Health Organization does in its classifications, is common. More than half of U.S. adults have a BMI above 25 (and) are either in an overweight or obesity classification,” said Hagan. “BMI does a poor job in a broad population level of predicting those health outcomes for an individual.” 

Hagan co-authored a perspective published last year that asks clinicians to do more than simple calculations such as BMI when advising patients about a healthy weight range. 

“Weight loss as a means to an end is not valid, in my view. We should be looking at improvements in other health outcomes and assessing the whole health of the individual.”

Download broadcast-ready soundbites with Hagan discussing body mass index.