The hydration fraction of fat-free mass can be calculated from the total body water and total body fat-free mass.



(1) total body water from deuterium dilution, in liters

(2) body volume from densitometry testing, in liters

(3) body weight in kilograms

(4) body ash from DEXA testing, in kilograms


hydration fraction of fat-free mass =

= (total body water) / (total body fat-free mass)


total body fat-free mass =

= (0.715 * (total body water)) + (3.07 * (body weight)) - (2.765 * (body volume)) - (1.469 * (body ash))


The mean hydration fraction for women is 0.745 and for men is 0.733.


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