Composition of lean tissue in healthy volunteers for nutritional studies in health and disease

Measurements of body composition were carried out on 56 healthy female volunteers 20–80 years of age.Anthropometric measurements were made to estimate lean body mass (ANLBM). Total body potassium (K) was measured from the naturally occuring 40K; body nitrogen (N) and calcium (Ca) were measured by neutron activation techniques. Body K, N and Ca reflect intracellular water, protein and bone mineral mass respectively.The 23 older women (mean (±SD) age=62.3±8.5) showed no significant differences from the 33 young adults (mean age 35.2±3.8) with respect to height, total body mass, ANLBM and intracellular water (K) but the older group had significantly less protein (by 17%) and less bone mineral (16%) than younger adults.When normalized for body size, based on height, ANLBM was significantly correlated to intracellular water (r=0.52) and to bone mineral (r=0.39) but correlated to either ANLBM (r=0.05) or to intracellular water (r=0.10). Protein was correlated to bone mineral (r=0.39).Simple anthropometric measurements may provide reasonable estimates of the fat and lean fractions of total body mass. However the composition of lean tissue varies with aging. To determine the essential components of lean tissue, direct measurements of protein and bone mass are required.