Leucine partially protects muscle mass and function during bed rest in middle-aged adults

Kirk L. English, Joni A. Mettler, Jennifer B. Ellison, Madonna M. Mamerow, Emily Arentson-Lantz, James M. Pattarini, Robert Ploutz-Snyder, Melinda Sheffield-Moore, Douglas Paddon-Jones

Research output: Contribution to journalArticlepeer-review

76 Scopus citations


Background: Physical inactivity triggers a rapid loss of muscle mass and function in older adults. Middle-aged adults show few phenotypic signs of aging yet may be more susceptible to inactivity than younger adults. Objective: The aim was to determine whether leucine, a stimulator of translation initiation and skeletal muscle protein synthesis (MPS), can protect skeletal muscle health during bed rest. Design: We used a randomized, double-blind, placebo-controlled trial to assess changes in skeletal MPS, cellular signaling, body composition, and skeletal muscle function in middle-aged adults (n = 19; age ± SEM: 52 ± 1 y) in response to leucine supplementation (LEU group: 0.06 g kg-1 meal-1) or an alanine control (CON group) during 14 d of bed rest. Results: Bed rest decreased postabsorptive MPS by 30% ± 9% (CON group) and by 10% ± 10% (LEU group) (main effect for time, P < 0.05), but no differences between groups with respect to pre-post changes (group time interactions) were detected for MPS or cell signaling. Leucine protected knee extensor peak torque (CON compared with LEU group: -15% ± 2% and -7% ± 3%; group time interaction, P < 0.05) and endurance (CON compared with LEU: -14% ± 3% and -2% ± 4%; group time interaction, P < 0.05), prevented an increase in body fat percentage (group 3 time interaction, P < 0.05), and reduced whole-body lean mass loss after 7 d (CON compared with LEU: -1.5 ± 0.3 and -0.8 ± 0.3 kg; group time interaction, P < 0.05) but not 14 d (CON compared with LEU: -1.5 ± 0.3 and -1.0 ± 0.3 kg) of bed rest. Leucine also maintained muscle quality (peak torque/kg leg lean mass) after 14 d of bed-rest inactivity (CON compared with LEU: 29% ± 2% and +1% ± 3%; group time interaction, P < 0.05). Conclusions: Bed rest has a profoundly negative effect on muscle metabolism, mass, and function in middle-aged adults. Leucine supplementation may partially protect muscle health during relatively brief periods of physical inactivity.

Original languageEnglish (US)
Pages (from-to)465-473
Number of pages9
JournalAmerican Journal of Clinical Nutrition
Issue number2
StatePublished - Feb 1 2016


  • Atrophy
  • Dietary supplementation
  • Nutrition
  • Physical inactivity
  • Skeletal muscle protein synthesis

ASJC Scopus subject areas

  • Medicine (miscellaneous)
  • Nutrition and Dietetics


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