You’ve probably heard of the BMI (Body Mass Index), which is a tool commonly used to determine if a person is at a healthy weight.
There’s a problem with that method – it is a simple height-to-weight ratio, and does not take into consideration one’s body composition. Athletes and bodybuilders with low body fat often are labeled as overweight or even obese on the BMI scale because they carry a lot of muscle.
Despite its flaws, the BMI has been used as a standard measure of individual health for years. According to the Centers for Disease Control and Prevention, a “healthy” BMI is 18.5-24.9, an overweight BMI is 25-29.9, and an obese BMI is 30 or higher.
In recent years, researchers have started to see that BMI is not such a good indicator of overall health after all.
Many U.S. companies use their employees’ BMIs as a factor in determining workers’ health care costs. And people with higher BMIs could soon have to pay higher health insurance premiums, if an Equal Employment Opportunity Commission (EEOC) rule which allows employers to penalize employees up to 30% of health insurance costs if they fail to meet ‘health’ criteria including a specified Body Mass Index (BMI) is adopted.
A new study led by UCLA psychologists has shown the serious implications of such policies.
The researchers found that using BMI to gauge health incorrectly labels an estimated 74,936,678 adults in the US as cardiometabolically unhealthy or cardiometabolically healthy.
Of that number, 54 million Americans have been classified as “unhealthy,” even though they are not.
The researchers’ findings are published online in the International Journal of Obesity.
A. Janet Tomiyama, an assistant professor of psychology in the UCLA College and the study’s lead author, said of the findings:
Many people see obesity as a death sentence. But the data show there are tens of millions of people who are overweight and obese and are perfectly healthy.
For the study, the link between BMI (which is calculated by dividing a person’s weight in kilograms by the square of the person’s height in meters) and several health markers, including blood pressure, glucose, insulin resistance, C-reactive protein levels, cholesterol, and triglyceride levels, was analyzed using data from the most recent National Health and Nutrition Examination Survey.
The researchers found that close to half of Americans who are considered “overweight” by virtue of their BMIs (47.4 percent, or 34.4 million people) are healthy, as are 19.8 million who are considered “obese.”
Given their health readings other than BMI, the people in both of those groups would be unlikely to incur higher medical expenses, and it would be unfair to charge them more for health care premiums, Tomiyama said.
Among the other findings:
- More than 30 percent of those with BMIs in the “normal” range — about 20.7 million people — are actually unhealthy based on their other health data.
- More than 2 million people who are considered “very obese” by virtue of having a BMI of 35 or higher are actually healthy. That’s about 15 percent of Americans who are classified as very obese.
Tomiyama, who directs UCLA’s Dieting, Stress and Health laboratory (DiSH), found in previous research that there was no clear connection between weight loss and health improvements related to hypertension, diabetes, and cholesterol and blood glucose levels.
She said she was surprised at the magnitude of the numbers in the latest study:
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. Employers, policy makers and insurance companies should focus on actual health markers.
Jeffrey Hunger, a co-author of the paper and a doctoral candidate at UC Santa Barbara, said the research shows that BMI is a deeply flawed measure of health:
This should be the final nail in the coffin for BMI.
Hunger recommends that people focus on eating a healthy diet and exercising regularly, rather than obsessing about their weight, and strongly opposes stigmatizing people who are overweight.
The proposed EEOC rule would allow employers to charge higher insurance rates to people whose BMI is 25 or higher. A BMI between 18.5 and 24.99 is considered normal, but the study emphasizes that normal BMI should not be the primary goal for maintaining good health.
Tomiyama is planning a new study of people with high BMIs who are very healthy.
If you would like to know if you are at a healthy weight, take your measurements periodically, notice how your clothes fit, and assess how you look and feel. If you can, check your body fat percentage periodically.
There are various ways to measure your body fat percentage. Two very accurate methods are DEXA scans or hydrostatic weighing, but they are only conducted at certain fitness and research facilities. Or, you can purchase a bioelectrical impedance scale skin fold caliper to measure your body fat at home. Two methods that don’t require any special equipment are taking progress pictures on a monthly basis to track differences, or using an online calculator like this one to estimate body fat.