Exercise and muscle performance are influenced by nutritional status and might be improved by nutrient supplementation
Short-term studies of up to 7 days have found that L-citrulline malate supplementation improves skeletal muscle metabolism and that the combination of L-citrulline and reduced glutathione (GSH) boosts plasma levels of L-citrulline, L-arginine and nitric oxide metabolites — compounds that support muscle mass.
L-citrulline is a non-essential amino acid, which is co-produced with nitric oxide and converted in the kidneys to L-arginine.
L-citrulline supplementation may boost L-arginine and nitric oxide more efficiently that L-arginine supplementation because its intestinal and hepatic metabolism is limited.
The ability of L-citrulline to support nitric oxide may be enhanced by GSH, which upregulates the nitric oxide pathway.
Researchers at Baylor University in Texas hypothesised that L-citrulline and GSH might act synergistically to improve body composition and muscle performance.
To evaluate this hypothesis, they conducted an 8-week, randomised, controlled trial. A total of 75 resistance-trained men were divided into three supplement groups: L-citrulline + GSH (200 mg/day of GSH + 2 g/day of L-citrulline); L-citrulline only (2g/day of L-citrulline-malate); or placebo.
L-citrulline and GSH (Sertria) were obtained from Kyowa Hakko Bio Co., Ltd. All participants also engaged in a supervised resistance training programme.
After 8 weeks, there were no significant differences between groups in change of muscle strength. There were also no significant differences in changes in total body mass, fat mass or total body water.
Lean mass was significantly greater in the L-citrulline + GSH group than placebo after 4 weeks.
Although lean mass was still greater in the L-citrulline + GSH group at 8 weeks, the difference from placebo was no longer significant. A significant correlation between lean mass and strength was only observed in the L-citrulline + GSH group. There were no significant changes in biochemical markers tested for safety.
More studies are needed to better understand the mechanisms of how L-citrulline and GSH relate to muscle mass and performance.
For now, the authors of this study conclude that 9-weeks of supplementation with L-citrulline + GSH increases lean muscle mass in resistance-trained males.