The Body Mass Index (BMI) was never intended to be an indicator of health.

You’re probably already familiar with the Body Mass Index. Maybe you’ve also heard how it’s not a good indicator of how healthy you are or what your ideal weight should be. Put simply, that’s because it’s true. The BMI wasn’t meant to be healthiness meter.

The main problem with the BMI is that it doesn’t measure the percentage of body fat. Moreover, it was never meant to. The BMI first came around in the mid 1800’s when Belgian polymath Adolphe Quetelet was developing “social physics.” He wasn’t developing anything geared to show a healthy weight for height. BMI actually defines a person’s body mass divided by the square of his or her height. It’s used more for medicinal purposes (determining dosage) than showing ideal weight. 

As seen in its numerous variations, the BMI also isn’t universal. Back in 1998 when the US National Institutes of Health and the CDC aligned US definitions of health with those of the World Health Organization, the BMI’s “normal” was changed, making some people suddenly overweight. The problem is obviously that the BMI is highly subjective, and while 25 million people in the US were factually overweight before 1998, the BMI didn’t say so until after. 

(Source)