BMI and Health
Body fat is relevant, not body mass
As far as health is concerned, excess body fat is negative. In contrast, an above-average muscle mass is more likely to be positive.
The BMI does not distinguish between body fat and fat-free mass. Yet statistics show that the body mass index of about 73 percent of the people is quite a significant indicator of the body fat percentage.
Thus, in three out of four cases, the BMI seems to have a significant relevance to health and in one out of four cases it does not seem to have any.
Body fat percentage vs. BMI
Despite its high relevance to health, the body fat percentage has its shortcomings. Scales for measuring body fat are simple to use but imprecise; the more accurate methods are very complicated and require skilled personnel.
The BMI, in contrast, can be calculated from two simple measurements which are reliable in most cases.
This seems to be the main reason why the BMI is still the most widely used value for estimating the body fat.