Tier 2 — strong

The effect of enteral glycine on plasma glycine and muscle structure, size, and function in the critically ill: A randomized controlled trial

Ali Abdelhamid Y, Bongetti AJ, Caldow MK, Karahalios A, Wittholz K, Fetterplace K, Beach LJ, Haines KJ, Tascone B, De Souza DP, Elahee Doomun SN, Presneill J, Rooyackers O, Koopman R, Lynch GS, Deane AM
Clinical nutrition (Edinburgh, Scotland) 2025 54:233-242

Bibliography

PubMed
PMID 41109034
DOI
10.1016/j.clnu.2025.10.001
Funding
Indexed support: Australian and New Zealand Intensive Care Foundation; National Health and Medical Research Council; The Royal Melbourne Hospital. See the publication for grant and funder details.
Competing interests
The accessible abstract does not establish the authors' competing interests; absence of a statement is not evidence of no conflicts.

Study snapshot

DesignRandomized controlled human intervention
ModelAdult humans
Sample29 mechanically ventilated adults: 10 placebo, 9 low-dose and 10 high-dose
InterventionEnteral glycine 0.2 or 0.4 g/kg/day versus placebo, alongside usual care
DurationUp to 7 days
EndpointsPlasma and muscle glycine; Quadriceps thickness; Myofiber diameter; Physical function and length of stay

What the study showed, in plain terms

A pilot ICU trial demonstrated that enteral glycine raises blood and muscle glycine. Effects on muscle preservation remain uncertain because the muscle-thickness comparison was not statistically significant.

Key findings

  • High-dose glycine increased both plasma exposure and muscle concentration.
  • The quadriceps-thickness difference versus placebo was 0.11 cm, with a confidence interval crossing zero.
  • Myofiber diameter did not improve; length-of-stay findings were exploratory.

What this study can and cannot tell us

Small trial not powered for definitive functional or clinical outcomes.

Critically ill patients receiving enteral doses cannot represent healthy adults taking bedtime glycine.

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Editorial review

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Dr. Khaled Mahmoud, MBBChCritical Care Medicine, Longevity Science & Editorial Direction