Carbohydrate versus protein The effects of varying the nutrient composition of meals have been studied extensively, rather more for mood than performance. This is largely because of evidence that plasma and brain levels of precursor amino-acids for the synthesis of monoamine neurotransmitters (chemicals responsible for signalling between nerve cells), strongly implicated in mood disorders, can depend on the ratio between carbohydrate and protein in the diet. Synthesis of the neurotransmitter serotonin (or 5-hydroxytryptamine (5-HT)) depends on the dietary availability of the precursor essential amino-acid, tryptophan, owing to a lack of saturation of the rate-limiting enzyme, tryptophan hydroxylase, which converts tryptophan to 5-hydroxytryptophan (see Figure 1). An important complication is that fpF^ LNAA WW
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