Why the BMI May Be a Flawed Measure of Health

A man stands on a scale
(Image credit: Niyazz/Shutterstock.com)

The body mass index, or BMI, may not be an accurate indicator of a person's risk of heart disease or diabetes, according to a new study.

The results suggest that about 75 million adults in the United States may be misclassified — they have a true risk of heart disease or diabetes that is either lower or higher than suggested by their BMIs, the researchers said.

The new results show that BMI is a flawed measure of health, they said.

To stay healthy, people should "prioritize eating well, staying active and getting enough sleep," rather than focus on their weight, said study co-author Jeffrey M. Hunger, a doctoral candidate at the University of California, Santa Barbara.

In the study, the researchers looked at the BMIs of about 40,000 adults in the U.S. They also looked at data on the people's "cardiometabolic health," which is their risk for heart disease and diabetes, including data on their blood pressure, blood sugar, cholesterol, inflammation and insulin levels. According to the definition adopted by the researchers, a person "is considered cardiometabolically healthy only if they have healthy values on four or more of these indicators," Hunger told Live Science.

When the researchers looked at the relationship between the people's BMIs and their cardiometabolic health, they found that nearly half of the people with a BMI in the overweight range, 29 percent of people with a BMI in the obese range and 16 percent of very obese people were cardiometabolically healthy. [Best BMI Calculator Apps]

"Many people see obesity as a death sentence," lead study author A. Janet Tomiyama, an assistant professor of psychology at the University of California, Los Angeles, said in a statement. "But the data show there are tens of millions of people who are overweight and obese and are perfectly healthy."

In addition, more than 30 percent of the people whose BMIs were considered in the normal weight range were found to be cardiometabolically unhealthy.

Previous research has also suggested that using BMI as a measure of health may be problematic. For example, a study published in 2010 in the International Journal of Obesity found that waist size was a better predictor than BMI of kids' future risk of heart disease. And another study, published in 2014 in the journal Pediatric Obesity, found that 25 percent of kids who were obese based on their body fat content were not labeled as obese based on their BMI.

The new study was published today (Feb. 4) in the International Journal of Obesity.

Follow Agata Blaszczak-Boxe on Twitter. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.

Staff Writer