So much for your BMI score

Now it’s everywhere, using an equation — essentially a ratio of mass to height — to categorize patients as overweight, underweight, or at a “healthy weight.” It’s appealingly simple, with a scale that designates adults who score between 18.5 and 24.9 as within a healthy range.

But critics — and they are widespread these days — say it was never meant as a health diagnostic tool. “BMI does not come from science or medicine,” said Dr. Fatima Stanford, an obesity medicine specialist and the equity director of the endocrine division at Massachusetts General Hospital.

She and other experts said BMI can be useful in tracking population-wide weight trends, but it falls short by failing to account for differences among ethnic groups, and it can target some people, including athletes, as overweight or obese because it does not distinguish between muscle mass and fat.