I enjoyed the book overall. that being said. I am an exercise physiologist, and when they were talking about body composition they mentioned use a bmi calculator to estimate body fat percentage. This is a highly inaccurate assessment that almost always is incorrect. It uses your entire mass including bone mineral density as well as your organ tissue and muscle tissue from your weight to guess you body fat without separating them, so it counts muscle as fat. almost every body builder and CrossFit athlete is classified as obese using this model. you would be better off doing a simple skin fold assessment at the 3 main sites for your sex to estimate body fat.