Age-related differences in fat-free mass, skeletal muscle, body cell mass and fat mass between 18 and 94 years

Objective: To determine (1) lean and fat body compartments, reflected by fa t-free mass (FFM), appendicular skeletal muscle mass (ASMM), body cell mass (BCM), total body potassium (TBK), fat mass and percentage fat mass, and t heir differences between age groups in healthy, physically active subjects from 18 to 94 y of age; and (2) if the rate of decrease in any one of the p arameters by age might be accelerated compared to others. Methods: A total of 433 healthy ambulatory Caucasians (253 men and 180 wome n) aged 18-94y were measured by dual-energy X-ray absorptiometry (DXA) and whole body scintillation counter (TBK counter) using a large sodium iodide crystal (203 ram diameter). Results: The ASMM change (-16.4 and -12.3% in men and women, respectively) in > 75 y-old compared to 18 to 34-y-old subjects was greater than the FFM change (-11.8 and -9.7% in men and women, respectively) and this suggests t hat skeletal muscle mass decrease in older subjects was proportionally grea ter than non-skeletal muscle mass. BCM (-25.1 and -23.2% in men and women, respectively) and TBK differences were greater than the differences in FFM or ASMM suggesting altered composition of FFM in older subjects. Women had lower peak FFM, ASMM, BCM and TBK than men. Conclusions: The decline in FFM, ASMM, BCM and TBK is accelerated in men an d women after 60 y of age and FFM, ASMM, BCM and TBK are significantly lowe r than in younger subjects. Fat mass continued to increase until around 75 y. Sponsorship: Foundation Nutrition 2000Plus, Geneva, Switzerland.