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Life 2014, 4(3), 295-317; doi:10.3390/life4030295
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Protein and Essential Amino Acids to Protect Musculoskeletal Health during Spaceflight: Evidence of a Paradox?

1,*  and 2
1 Department of Health, Nutrition, and Exercise Sciences, North Dakota State University, Fargo, ND 58102, USA 2 Exercise Physiology and Countermeasures Laboratory, JES Tech, Houston, TX 77058, USA
* Author to whom correspondence should be addressed.
Received: 13 March 2014 / Revised: 19 June 2014 / Accepted: 23 June 2014 / Published: 11 July 2014
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
View Full-Text   |   Download PDF [736 KB, 15 July 2014; original version 11 July 2014]

Abstract

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∙kg1∙day1) and spaceflight is associated with reduced energy intake (~20%), which enhances muscle catabolism. Increasing protein intake to 1.5–2.0 g∙kg1∙day1 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.
Keywords: spaceflight; exercise countermeasures; skeletal muscle; bone; amino acids; leucine; disuse; unloading spaceflight; exercise countermeasures; skeletal muscle; bone; amino acids; leucine; disuse; unloading
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Hackney, K.J.; English, K.L. Protein and Essential Amino Acids to Protect Musculoskeletal Health during Spaceflight: Evidence of a Paradox? Life 2014, 4, 295-317.

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