Reasons for Leaving out L-tryptophan

Reason # 1

Reason Number 1 for leaving out L-tryptophan involves its role in muscle anabolism. While it is true that tryptophan stimulates protein synthesis when it's part of an essential amino acid (EAA) or mixed amino acid (AA) mixture, it's effects are mainly on liver protein synthesis. Recent studies had shown that L-tryptophan along with tyrosine) has negligible effects on skeletal muscle protein synthesis and in fact, because of its effects on hepatic protein synthesis, is counterproductive if your goal is to maximize muscle protein synthesis. Increasing liver protein synthesis is robbing Peter (muscle) to pay Paul (liver).

Reason # 2

Reason Number 2 for leaving out L-tryptophan. One rationale for using it in a post exercise AA mixture is that it increases serotonin levels and as such provides a relaxing effect after training. Well. this is not the case. Large neutral amino acids such as the BCAAs compete with tryptophan for transport across the blood-brain barrier and hence CNS levels of tryptophan do not increase significantly, leaving more of the tryptophan in the system - which is exactly what we don't want if the aim is to maximize skeletal muscle protein synthesis.