BMI isn't a measure of body fat. How many fat people are there really? In this study of 4,745 participants, measured with DXA scans, only 9.6% had a normal body fat percentage. (10.5% for men and 8.8% for women.) (The data is from 2003-2006.) Normal BF% was defined as 5% to 20% for men and as 8% to 30% for women.  Using BMI, there is an estimated 1.7% of underweight adults in the US. (1% for men and 2.4% for women, in 2010) The real percentage of fat adults, in the US, may be over 90%. Would you like to know more?