Overview :

If total body water is known from using antipyrine or other marker, then the formula of Pace and Rathbun can be used to estimate the lean body mass. Water was found to constitute 72.4% of the fat-free (lean) body mass.

lean body mass =

= (total body water ) / (percentage of lean body mass as total body water) =

= (total body water ) / (0.73) =

= (total body water) * 1.37

This is a rearrangement of the equation:

total body water as percent of lean body weight =

= (total body water) / (lean body mass) * 100%

Hume R, Weyers E. Relationship between total body water and surface area in normal and obese subjects. J Clin Path. 1971; 24: 234-238.

Mollison PL. Blood Transfusion in Clinical Medicine, 7th edition. Blackwell Scientific Publications. 1983. page 79 [in the book, the formula is "TBW * 0.73" which is incorrect]

Pace N, Rathbun EN. Studies on body composition. III. The body water and chemically combined nitrogen content in relation to fat content. J Biol Chem. 1945; 158: 685-691.