The once-vaunted BMI — used for decades as a measure of healthy weight — is about to go the way of the 8-track tape player and VHS recorder.
New research out of the University of California-Santa Barbara suggests if your weight is above average for your height, based on your BMI, it doesn’t necessarily mean you’re overweight, obese, or unhealthy.
In what many experts regard as the death knell for the BMI (body mass index), UCSB psychologist Jeffrey Hunger and colleagues argue 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 this month, 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. 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, a Belgian mathematician and scientist born in 1796. Quetelet studied population groups globally, designing BMI to aid his research. But the tool was originally designed to measure and compare societies, not individuals.
A growing number of researchers, including Hunger, have suggested in recent years that basing on weight and height only isn’t a good way to measure obesity or a person’s overall health.
For one thing, the index doesn’t accurately measure body fat content to highlight critical health factors such as fat distribution and proportion of muscle to fat. Nor does the BMI take into account gender and racial differences in body composition.
Health experts also note that where fat occurs on a person’s body is every bit as important to health as how much they weigh. Abdominal fat is closely linked with a greater risk for diabetes and heart disease than other types of fat.
In addition, the BMI treats body weight the same, no matter what it’s comprised of — fat, muscle, bone, or other tissues. In fact, 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, M.D., 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 health markers that experts recommend that provide a broader picture of a person’s health than BMI:
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.
Waist measurements. Simply taking a tape measure to check your waist size can 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.
Vital signs and health numbers. Health experts say blood tests to check for cholesterol levels, blood glucose, and hypertension are more reliable ways to gauge your overall health than the BMI, along with measures of your heart rate and pulse. For some individuals other tests can also be helpful — such as measurements of hormone levels, heart function, and cardiovascular fitness.
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.
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