The Truth About Your BMI
The best way to check if your weight is healthy is to calculate your body-mass index (BMI), right? Not necessarily, according to a perspective recently published in the journal Science: It argues that BMI isn't an accurate measure of metabolic health.
In the perspective, two researchers from the Perelman School of Medicine at the University of Pennsylvania write that BMI doesn't tell the whole story. "The fact is that BMI basically reflects your weight and height," says co-author Rexford Ahima, M.D., Ph.D., a professor of medicine and the director of the Obesity Unit in the Institute for Diabetes, Obesity, and Metabolism at the University of Pennsylvania. A few of the many things it does not reflect: your family history, muscle mass, and where your excess fat is located.
While this isn't exactly breaking news--researchers have known that BMI gives only a very limited indication of overall health for a while now--it's a good reminder not to get too caught up in any one number, including this one. Here's why:
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How Your BMI Can be Off
Since muscle weighs more than fat, a really strong person's BMI could be higher than the BMI of a really weak person who has the same general height and build--but that doesn't make the strong person any less healthy.
Distribution of fat is also a major factor in terms of your metabolic health. Overweight people can have healthy blood pressure, lipid, blood sugar, and cholesterol levels, although that's most likely to be the case if they have less belly fat and more subcutaneous fat (fat under the skin), says Ahima. So while an overweight person's BMI might seem unhealthy, they may not actually have a high risk for many diseases if their fat is primarily subcutaneous.
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What You Should Use Instead
For all of those reasons, your BMI should only be one of many tools in your box of health assessments, says Ahima. Another tool, for example, is your waist circumference. Ahima says that it's a better measure of abdominal fat and that women should be wary of any number above 35 inches. Ask your doctor to take this measurement for you to get the most accurate read.
You should also be aware of the blood measurements that predict disease (your blood lipid, blood sugar, and cholesterol levels, for example), as well as your family history of diabetes, heart disease, and cholesterol problems, says Ahima. "Regardless of your BMI, if you have a father, a mother, or a sibling who has diabetes, that puts you at risk for diabetes--especially type-2 diabetes."
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By Alison Goldman, Women's Health
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