Tryptophan Availability and Serotonin Synthesis

Under carefully chosen experimental conditions, the consumption of specific diets or the administration of appropriate precursor amino acids can influence the synthesis of serotonin and catecholamines in the brain Thus, if rats are starved overnight and then given a carbohydrate-rich, protein-free meal, brain serotonin ( 5-hydroxytryptamine, 5HT) increases; if the meal is rich in protein, brain gHT may fall (Fernstrom Leathwood, 1986). The mechanism by which diet (or tryptophan; TRP) is thought to influence 5HT synthesis involves the following sequence: the composition of food consumed changes plasma levels of the large neutral amino acids (LNAA), which affect in turn the rate of TRP transport into the brain, brain TRP levels and hence the rate of 5HT synthesis. It has been suggested that, by this mechanism, dietary interventions might influence a range of behaviours and brain functions linked to serotoninergic neurotransmission. The objective of the present review is to examine each step in the long sequence of (proposed) causality in an attempt to define the circumstances under which each step may have functional significance.