Four-compartment model of body composition of normal elderly women

A group of 186 apparently normal women was divided into three age groups (average ages 65.3 +/- 4.4, 74.7 +/- 5.5, and 80.9 +/- 4.2 years, respectively) and their body composition was studied using dual-energy X-ray absorptiometry. The fat, fat-free, and mineral components were quantitated, and the fat-free compartment was calculated to define a four-compartment model of body composition (fat, fat-free, mineral, and water). Fat decreases with age, as shown by the comparison of the group whose average age was 75 years with the 65-year-old group (p < 0.01) and 80-year-old group (p < 0.005). Soft-tissue mass was greater in the 80-year-old group (p < 0.025) than in the 75-year-old group. Water was lower in the two older groups (p < 0.02 and p < 0.005, respectively), and the mineral component showed no differences. The decreased fat, increased soft tissues, and absence of changes in the mineral component may be related to an improvement in habits and lifestyle in recent years.