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

Klaas R Westerterp*, Yosuke Yamada, Hiroyuki Sagayama, Philip N Ainslie, Lene F Andersen, Liam J Anderson, Lenore Arab, Issaad Baddou, Kweku Bedu-Addo, Ellen E Blaak, Stephane Blanc, Alberto G Bonomi, Carlijn V C Bouten, Pascal Bovet, Maciej S Buchowski, Nancy F Butte, Stefan G J A Camps, Graeme L Close, Jamie A Cooper, Sai K DasRichard Cooper, Lara R Dugas, Ulf Ekelund, Sonja Entringer, Terrence Forrester, Barry W Fudge, Annelies H Goris, Michael Gurven, Catherine Hambly, Asmaa El Hamdouchi, Marije B Hoos, Sumei Hu, Noorjehan Joonas, Annemiek M Joosen, Peter Katzmarzyk, Kitty P Kempen, Misaka Kimura, William E Kraus, Robert F Kushner, Estelle V Lambert, William R Leonard, Nader Lessan, Corby K Martin, Anine C Medin, Erwin P Meijer, James C Morehen, James P Morton, International Atomic Energy Agency Doubly Labeled Water database group, Guy Plasqui, Giulio Valenti, Ludo M. Van Etten, Edgar A Van Mil, John R. Speakman*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

5 Citations (Web of Science)


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.

Original languageEnglish
Pages (from-to)1583-1589
Number of pages7
JournalAmerican Journal of Clinical Nutrition
Issue number5
Publication statusPublished - 8 Nov 2021


  • physical activity level
  • age
  • energy expenditure
  • body composition
  • doubly labeled water
  • AGE

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