Bye-Bye BMI: 3 Obesity Tests Better Than Body Mass Index

If you’re still using the BMI — body mass index — to determine if you’re dangerously overweight, you might as well be listening to music on an 8-track tape player or watching movies on an old VHS recorder.

That’s because the latest research shows that once-vaunted BMI is as outmoded as those old audio-video technologies and that other methods are far better at obesity-related risks for heart attack or other health problems.

A new study, published last month in the Journal of the American Heart Association, found that one newer type of obesity measurement — called a waist-to-hip ratio test — is a far better way to calculate excessive body fat than the BMI.

To reach their conclusions, British researchers tracked 265,988 women and 213,622 men and found individuals — particularly women — with a bigger waist-to-hip ratio face greater risks of experiencing a heart attack than those who don’t.

Lead researcher Sanne Peters, of the George Institute for Global Health and the University of Oxford in the U.K., explained that waist-to-hip ratio tests are a better measure of how and where fat tissue is distributed in the body than BMI.

“Waist‐to‐hip ratio was more strongly associated with the risk of [heart attack] than body mass index in both sexes, especially in women,” reported Peters and his colleagues.

The British study is only the latest research to question the value of BMI tests. University of California-Santa Barbara scientists also recently found that an elevated BMI isn’t the best way to determine if you’re overweight, obese, or unhealthy.

UCSB psychologist Jeffrey Hunger and colleagues said their work shows that you can be fit and still be considered overweight by BMI guidelines.

In fact, the UCSB research, published in the International Journal of Obesity, indicates nearly 35 million Americans labeled overweight or obese based on their BMI are, in fact, "perfectly healthy" — as are 19.8 million others considered obese.

"In the overweight BMI category, 47 percent are perfectly healthy," said Hunger, a doctoral student in UCSB's Department of Psychological & Brain Sciences, arguing that BMI is a deeply flawed measure of health and should be abandoned.

"So to be using BMI as a health proxy — particularly for everyone within that category — is simply incorrect,” he said. “Our study should be the final nail in the coffin for BMI."

The BMI — calculated by dividing a person's weight in kilograms by the square of the person's height in meters — was developed by Adolphe Quetelet, an 18th century Belgian mathematician. But the tool was originally designed to measure and compare societies, not individuals.

A growing number of researchers, including Hunger, have suggested measuring weight and height only isn’t a good way to gauge obesity or a person’s overall health.

For one thing, the index doesn’t accurately measure body fat content or distribution on the body, or the proportion of muscle to fat — all critical factors in determining obesity-related health risks. Nor does the BMI take into account gender and racial differences in body composition.

The BMI treats body weight the same, no matter what it’s comprised of — fat, muscle, bone, or other tissues. As a result, many people who are very muscular can be falsely labeled overweight or obese by the BMI, while those who fall within BMI’s weight parameters may have high levels of body fat content.

Declaring a person obese based only on BMI, “is old-fashioned and not terribly useful,” said Dr. Scott Kahan, director of the National Center for Weight and Wellness in Washington, D.C. He sees patients who are deemed overweight by the BMI, but are healthy and well.

“They’re heavy,” he noted. “BMI puts them in the obesity range. And yet on every level
their health is actually good. Cholesterol and blood pressure are excellent. Blood sugar is excellent. They don’t seem to have any health effects associated with excess weight.”

So what alternatives can be used in place of BMI to more accurately measure health and obesity? Here’s are a few tests experts recommend that provide a broader picture of a person’s health than BMI:

Waist-to-hip ratio. This test calculates how much excess weight you are carrying, which can indicate your susceptibility to high blood pressure, heart disease, and diabetes. To calculate your waist-to-hip ratio, use a tape measure to measure the size of your waist line and the widest part of your hips. Then divide the circumference of your waist by your hip measurement. Men with a waist–to-hip ratio above 0.90 and women over 0.85 are considered obese, according to the World Health Organization.

Waist measurements. Simply taking a tape measure to check your waist size can also provide a clue to whether you need to lose weight. Generally, a waist size over 35 inches in women and 40 inches in men indicates that weight loss is warranted, with the exception of only the most muscular individuals.

Body-fat content tests. Instruments such as DEXA (dual-energy X-ray absorptiometry) scanners — becoming more widely available at health clubs and clinics — provide a highly accurate measurement of body fat and lean mass distribution. They can also reveal important information about bone health.

In addition to these tests, health experts say measurements of other vital signs and health numbers are more reliable ways to gauge your overall health than the BMI. Among them:

• Blood tests to check for cholesterol levels, blood glucose, and hypertension.
• Measures of your heart rate and pulse.
• Screenings for hormone levels, heart function, and cardiovascular fitness.

UCSB Hunger argued that the idea of using a single measurement, such as the BMI, as a gauge overall health is outmoded and should be abandoned.

"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," he said.