AJP - Endocrinology and Metabolism, Vol 272, Issue 5 E781-E787, Copyright © 1997 by American Physiological Society
Density of fat-free body mass: relationship with race, age, and level of body fatness
M. Visser, D. Gallagher, P. Deurenberg, J. Wang, R. N. Pierson Jr and S. B. Heymsfield
Department of Human Nutrition, Wageningen Agricultural University, The Netherlands.
The two-compartment body composition method assumes that fat-free body mass
(FFM) has a density of 1.100 kg/l. This study tested the hypothesis that
FFM density is independent of race, age, and body fatness. Subjects were
703 black and white subjects, ages 20-94 yr, with body mass index (BMI)
17-35 kg/m2. Body composition was assessed using a four-compartment model
based on tritium dilution volume, body density by underwater weighing, bone
mineral by dual-energy X-ray absorptiometry, and body weight. No
relationship was observed between FFM density and race or BMI. A tendency
was observed for a lower FFM density only in older white women. The
difference in percent body fat (delta fat) between the four-compartment
model and underwater weighing was < 2% for all groups. Race, age, and
BMI explained only 2.3 (women) and 1.4% (men) of the variance in delta fat,
whereas the total body water fraction of FFM explained 77%. In contrast to
current thinking, these results show that the assumption of constant FFM
density is valid in black, elderly, and obese subjects.
