How BMI is not a perfect tool?

Answer 1

It doesn't factor in muscle mass, which is more dense than fat is. Notice how some bodybuilders or professional football players can weigh a lot. If you took some of their BMI's, they would probably almost all fit into the overweight or obese range. However, they aren't overweight at all, and not unhealthy, but BMI would say they were. That's why, in some cases, a body fat test is more accurate, and BMI should just be used as a general guideline. Take it with a grain of salt!

Answer 2

It doesn't take muscle mass into account. Muscle is much more dense and compact than fat is. That's why most bodybuilders have really high body weights. They're considered "overweight" by BMI standards, but their weight is mainly made up of muscle mass and very little fat. Yet BMI says they are overweight, when they're actually the total opposite. The more accurate thing to do is to get a body fat test done.