Plot of the fat fraction as a function of 1/density for males ages 18 to 89 (top panel) and females ages 18 to 90 (bottom). The black line is the optimal least square linear fit to the data. The other lines are the predictions using the Siri I (eq. (13), blue), Siri II (eq. (14), red) and Brozek (eq. (15), green) relations.