Although traditionally considered a nonessential amino acid, L-GIn is now considered 'conditionally essential' during periods of metabolic stress characterised by catab-olism and negative nitrogen balance. Critical illness, stress, and injury can lead to a significant decrease in plasma levels of L-GIn, which if severe can increase the risk of mortality (Boelens et al 2001, Wischmeyer 2003).
Prolonged protein malnutrition may cause growth inhibition, muscle wasting and organ damage (Kohlmeier 2003). In the absence of sufficient plasma glutamine the body will break down skeletal muscle stores, and gut integrity (gut mucosal barrier function) and immunity will be compromised. Because L-GIn is utilised during exercise a more recent phenomenon of deficiency has been explored and glutamine depletion has been linked with 'overtraining syndrome'.
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