Chances are it has been a while since you last checked your body mass index, or BMI.
It’s an important number, yet it’s also one health experts aren’t so sure is an accurate indicator of health — despite the big push for a healthy BMI.
People with the lowest BMI had a 44 to 45 percent higher risk of dying early than those with more average BMIs.
A healthy weight is a BMI of 18.5 to 24.9; overweight is considered 25 to 29.9; and obese is 30 or higher, according to the National Institutes of Health.
A recent study that examined BMI and death rates of 55,000 Canadians found that the thinnest people and those with the most fat had higher death rates. So being thinner doesn’t necessarily make you healthier — but neither does having too much fat.
Unlike other studies, though, the researchers didn’t rely solely on BMI. They looked at total body fat directly and followed up over a seven-year period on a pool of white participants; females had a mean age of 63.5 and men had a mean age of 65.5. Basically, those with the lowest BMI had a 44 to 45 percent higher risk of dying earlier than those with more average BMIs. Those with the highest fat composition, regardless of BMI, had higher death rates, too.
A small subset of the individuals in the study had both excess fat and low BMI because of inadequate muscle — something the study author told CNN was a “double whammy in terms of adverse effects on health.”
For people with high BMIs, it’s likely due to increased levels of fat, not muscle, Sharon Palmer, a California-based dietitian and author of “Plant-Powered for Life” wrote in Today’s Dietitian. “The evidence that BMI is a good predictor of disease risk isn’t as conclusive as some experts may hope,” she wrote.
“BMI does provide some indication of mortality risk but it’s not the whole story,” a study author said.
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In her article, Ruth Frechman, a spokesperson for the Academy of Nutrition and Dietetics, said BMI is only a ratio for weight and height but is not an indicator of body fat. Though it can be useful, Dr. Francisco Lopez-Jimenez, a professor of medicine at the Mayo College of Medicine, said waist-to-hip ratio is also a useful detector of obesity-related risk.
That said, BMI still seems to be pushed by medical organizations as the go-to indicator of healthy weight and overall health.
Dr. Scott Kahan, director of the National Center for Weight and Wellness in Washington, D.C., said he’s fascinated by the confusion and emotion surrounding BMI.
“BMI is neither ‘good’ nor ‘bad,'” he said. “A ‘normal’ BMI does not connote ‘healthy,’ nor does an ‘abnormal’ BMI connote ‘”unhealthy.'”
BMI should neither be used as an absolute indication of anything, nor should it be abandoned as useless, Kahan said.
He said some people with a BMI over 30, which puts them in the “obese” category, have normal levels of body fat but high muscle. A lot of people with normal BMIs have elevated body fat because they have less muscle or bone.
Rosemary Logue, a dietitian from Dover, New Jersey, said BMI is a calculation based solely on height and weight.
“It does not take into consideration body composition,” she noted. “Since muscle is heavier and more dense than fat, if someone is very muscular, fit, and healthy, that person may have a higher BMI and be classified as ‘overweight.’ The reverse is also true; there are some very unhealthy people with ‘normal’ BMIs. A smoker with a BMI of 21 is probably less healthy than an athlete with a BMI of 30.”
Watch Your Wellness
The Canadian study may help more people understand that a higher BMI doesn’t necessarily mean a higher death rate.
“Most importantly — the repeated, often vehement, arguments about BMI being good or bad should be stopped. It’s both and it’s neither,” Kahan said.
[lz_bulleted_list title=”Calculate your BMI” source=”http://www.webmd.com”]Divide your weight in pounds by your height in inches squared|Multiply by 703|Weight ÷ (Height)2 x 703=BMI[/lz_bulleted_list]
BMI has been hyped as the only number we need to pay attention to, Dr. Mike Sevilla, a family physician from Salem, Ohio, told LifeZette.
“As more scientific studies are released, we’re finding our advice is correct: There is no one number to focus all of your efforts on,” Sevilla said. He added that family history, blood sugar, and blood pressure — especially with tobacco use — are other factors that can gauge overall health.
Dr. William D. Leslie, professor of medicine and radiology at the University of Manitoba and author of the study, said it’s important to look at a person’s body composition, as weight can be attributed to fat or healthy tissue.
“BMI remains a valuable and well-studied index of body weight and health,” he said. “It does provide some indication of mortality risk, but it’s clearly not the whole story.”