To get your body fat percentage low enough while remaining in a healthy range, the ratio of protein to carbs to fat you consume matters. (homefitnessguru.net)
To sustain his growth and large bones, you want a higher fat percentage as well, around 20 %. (dogcare.dailypuppy.com)
This is because women generally need a body fat percentage of at least 20 percent in order to remain fertile and have regular menstrual cycles. (mindbodygreen.com)