Tens of millions of people labeled overweight or obese by the body mass index (BMI) scale might soon feel vindicated.
According to a new study from the University of California Santa Barbara (UCSB) and the University of California Los Angeles (UCLA), about 34 million people labeled "overweight" and about 20 million people labeled "obese" by the BMI scale might be just fine the way they are.
BMI is a measurement of a person's size that divides weight (in kilograms) by height squared (in meters). A person with a BMI above 25, such as someone who is 5'4" and weighs more than 145 pounds, is considered overweight. At 174 pounds, which results in a BMI of 30, a person of the same height is considered obese. A person who is 5'10" is considered overweight at 174 pounds and obese at 202 pounds.
According to the Centers for Disease Control and Prevention (CDC), BMI does not measure body fat, but the numbers do seem to correlate with certain diseases caused by excess weight. However, these study authors say that almost half of the people labeled overweight by the BMI scale are "perfectly healthy," according to a press release from UCSB.
"In the overweight BMI category, 47 percent are perfectly healthy," study co-author Jeffrey Hunger, a doctoral student in UCSB's Department of Psychological & Brain Sciences, said in the press release. "So to be using BMI as a health proxy -- particularly for everyone within that category -- is simply incorrect. Our study should be the final nail in the coffin for BMI."
The researchers analyzed data from 2005 to 2012 from the National Health and Nutrition Examination Survey, a program by the Centers for Disease Control and Prevention (CDC) that interviews and examines a representative sample of 5,000 people in 15 counties across the United States.
Study authors compared BMI to five health markers: blood pressure, cholesterol; and levels of blood sugar, triglyceride (a type of fat) and C-reactive protein (a protein produced by the liver) in the blood. Out of five indicators, a subject had to pass four of them to be considered healthy.
The researchers found that not only are many who are considered overweight, obese or very obese healthy, but that 27 million people who are considered a healthy weight are actually unhealthy. Two million people who are very obese, or a BMI higher than 35, are healthy.
"Not only does BMI mislabel 54 million heavier individuals as unhealthy, it actually overlooks a large group of individuals considered to have a 'healthy' BMI who are actually unhealthy when you look at underlying clinical indicators," Hunger said in the release.
The study authors hope their findings could mean that those above a BMI of 25 would not be punished, such as by paying higher health insurance costs.
“There are healthy people who could be penalized based on a faulty health measure, while the unhealthy people of normal weight will fly under the radar and won’t get charged more for their health insurance,” A. Janet Tomiyama, an assistant professor of psychology at UCLA, said in a press release from UCLA. “Employers, policy makers and insurance companies should focus on actual health markers.”
Hunger hopes that this study can motivate people to focus on healthy behaviors instead of the number on the scale.
"We need to move away from trying to find a single metric on which to penalize or incentivize people and instead focus on finding effective ways to improve behaviors known to have positive outcomes over time," Hunger said in the release.
This study was published February 4 in the International Journal of Obesity.
Funding sources and disclosures were unavailable at time of publication.