Density and composition of the lean body compartment and its relationship to fatness

Abstract

Specific gravity of the eviscerated carcass was determined by water displacement on 26 male and 21 female adult guinea pigs. Fat (petroleum ether extraction) and water (freeze-drying) were determined on the entire body, and total adipose tissue was estimated. Specific gravity of the fat-free body (FFB) and the adipose-free body (AFB) was calculated for this and other studies on steers and rats where possible. Specific gravity of the FFB ranged around 1.09 ± 004–008 (mean ± sd) and was independent of weight of the FFB but possibly correlated with fatness. Specific gravity of the AFB was approximately 1.10 with the same order of variability. Purely biological variability must be smaller and indicates physiological regulation. The H₂O_FFB was 75% (guinea pig) and 71% (steer) with standard deviations of around 1%. Positive correlations between fatness and weight of both FFB and AFB in this population study corroborate similar findings in in vivo studies on man. Increments in fat, lipocytes, and nonadipose material were in the ratio 60:12:28. Indirect evidence indicates participation of bone in short-term weight changes. A mechanism is suggested for regulation of muscle:bone ratio and specific gravity in the AFB.