Physical activity and fat-free mass during growth and in later life

Am J Clin Nutr. 2021 Nov 8;114(5):1583-1589. doi: 10.1093/ajcn/nqab260.

Abstract

Background: Physical activity may be a way to increase and maintain fat-free mass (FFM) in later life, similar to the prevention of fractures by increasing peak bone mass.

Objectives: A study is presented of the association between FFM and physical activity in relation to age.

Methods: In a cross-sectional study, FFM was analyzed in relation to physical activity in a large participant group as compiled in the International Atomic Energy Agency Doubly Labeled Water database. The database included 2000 participants, age 3-96 y, with measurements of total energy expenditure (TEE) and resting energy expenditure (REE) to allow calculation of physical activity level (PAL = TEE/REE), and calculation of FFM from isotope dilution.

Results: PAL was a main determinant of body composition at all ages. Models with age, fat mass (FM), and PAL explained 76% and 85% of the variation in FFM in females and males < 18 y old, and 32% and 47% of the variation in FFM in females and males ≥ 18 y old, respectively. In participants < 18 y old, mean FM-adjusted FFM was 1.7 kg (95% CI: 0.1, 3.2 kg) and 3.4 kg (95% CI: 1.0, 5.6 kg) higher in a very active participant with PAL = 2.0 than in a sedentary participant with PAL = 1.5, for females and males, respectively. At age 18 y, height and FM-adjusted FFM was 3.6 kg (95% CI: 2.8, 4.4 kg) and 4.4 kg (95% CI: 3.2, 5.7 kg) higher, and at age 80 y 0.7 kg (95% CI: -0.2, 1.7 kg) and 1.0 kg (95% CI: -0.1, 2.1 kg) higher, in a participant with PAL = 2.0 than in a participant with PAL = 1.5, for females and males, respectively.

Conclusions: If these associations are causal, they suggest physical activity is a major determinant of body composition as reflected in peak FFM, and that a physically active lifestyle can only partly protect against loss of FFM in aging adults.

Keywords: age; body composition; doubly labeled water; energy expenditure; physical activity level.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adipose Tissue / metabolism*
  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Body Composition*
  • Child
  • Child, Preschool
  • Cross-Sectional Studies
  • Energy Metabolism
  • Exercise*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Young Adult