New research shows that the Body Mass Index — BMI for short — isn’t the surefire way to determine whether a person is healthy or not that we’ve been thinking it is.

As this story from theweek,com shows, being fat yet fit is just as possible as being what’s considered the right weight and not in great health.

First, a little reminder of just what the BMI is. Divide a person’s weight by the square of their height to get an individual’s number. (Go ahead; figure out yours here.) “Healthy” is a BMI between 18.5 and 24.9; 25 to 29.9 is said to be “overweight” and anything 30 or over is classified as “obese,” according to the Index.

For a while now, the complaint has been that that number alone doesn’t really tell enough about one’s well-being. And that’s just what the new study, reported in story says. When you plug that figure in along with other data — blood pressure, glucose, insulin resistance, triglycerides, among others — almost half of the overweight, 29 percent of the obese and 16 percent of what is the very obese were healthy, according to the study, publicized in the International Journal of Obesity.

Possibly even more importantly, more than 30 percent of normal weight persons were found to be unhealthy. So that means they’re walking around thin and thinking all is well with them, leaving them quite vulnerable, I’d say.

This all matters for another very good reason. The Equal Employment Opportunity Commission has been suggesting rules that would let employers penalize their workers up to 30 percent of health insurance fees if they didn’t meet certain standards, such as getting to a specific BMI. No! That arbitrary number should not be used to fine people when it is so faulty.

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