Impact of Fat-Free Mass Quality and Detailed Body Composition on Changes of Resting Energy Expenditure with Age

Abstract

Purpose

Resting energy expenditure (REE) and fat-free mass (FFM) change from childhood to adulthood. Since FFM is the major predictor of REE, age-related changes in body composition have been proposed to explain changes in REE.

Recent Findings

Beside its mass, FFM composition also changes with age. FFM is composed of (i) chemical components (protein, total water, and minerals) and (ii) anatomical components, i.e., organ and tissue masses, both of which change with age. In addition, during aging, specific metabolic rates of organs and tissues also decline. In elderly subjects, about 88.0% of the variance in REE is explained by age-related changes in masses, their composition, and specific metabolic rates. However, about 12% of the variance in REE remains unexplained. The residuals in the REE-FFM relationship are associated with metabolic disturbances, and negative residuals are related to "healthy" aging.

Summary

Age-related changes in body composition explain most of the variance in metabolic changes. The variances in REE are associated with health.

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