Fig. 1
From: The role of serotonin and diet in the prevalence of irritable bowel syndrome: a systematic review
Tryptophan Metabolism: Tryptophan is a substrate for the large neutral amino-acid transporter system and competes for transport with several other amino acids essential for brain function. Once in the CNS, L-tryptophan is hydroxylated to 5-hydroxytryptophan by the enzyme tryptophan hydroxylase type 2, the rate-limiting step in the brain serotonin synthesis. This is followed by subsequent decarboxylation involving the enzyme L-aromatic acid decarboxylase to serotonin (5-hydroxytryptamine, 5-HT)