Protein and essential amino acids to protect musculoskeletal health during spaceflight: Evidence of a paradox?

Kyle J. Hackney, Kirk L. English

Research output: Contribution to journalReview articlepeer-review

12 Scopus citations


Long-duration spaceflight results in muscle atrophy and a loss of bone mineral density. In skeletal muscle tissue, acute exercise and protein (e.g., essential amino acids) stimulate anabolic pathways (e.g., muscle protein synthesis) both independently and synergistically to maintain neutral or positive net muscle protein balance. Protein intake in space is recommended to be 12%-15% of total energy intake (≤1.4 g·kg-1·day-1) and spaceflight is associated with reduced energy intake (~20%), which enhances muscle catabolism. Increasing protein intake to 1.5-2.0 g·kg-1·day-1 may be beneficial for skeletal muscle tissue and could be accomplished with essential amino acid supplementation. However, increased consumption of sulfur-containing amino acids is associated with increased bone resorption, which creates a dilemma for musculoskeletal countermeasures, whereby optimizing skeletal muscle parameters via essential amino acid supplementation may worsen bone outcomes. To protect both muscle and bone health, future unloading studies should evaluate increased protein intake via non-sulfur containing essential amino acids or leucine in combination with exercise countermeasures and the concomitant influence of reduced energy intake.

Original languageEnglish (US)
Pages (from-to)295-317
Number of pages23
Issue number3
StatePublished - Jul 11 2014
Externally publishedYes


  • Amino acids
  • Bone
  • Disuse
  • Exercise countermeasures
  • Leucine
  • Skeletal muscle
  • Spaceflight
  • Unloading

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Biochemistry, Genetics and Molecular Biology(all)
  • Space and Planetary Science
  • Palaeontology


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