|Poultry is high in tryptophan and so is spirulina, cod, soy beans, parmesan and pork. They all have higher tryptophan contents than turkey. So, it doesn't always have to be poultry ;-)|
Until today, l-tryptophan, the amino acid the "happy neurotransmitter" serotonin is not among the usual suspects when it comes to building muscle. If the results of a recent study from the Georgia Regents Univ. translate into practic-ally relevant research, this may change soon (Dukes. 2015).
The aim of said study was to test the hypothesis that the essential amino acid tryptophan, and its metabolite kynurenine, might directly affect muscle metabolism in the setting of protein deficiency. To this ends, adult mice (12 mo) were fed a normal diet (18% protein), as well as diets with low protein (8%) supplemented with increasing concentrations (50, 100, and 200 uM) of kynurenine (Kyn) or tryptophan (Trp; 1.5 mM) for 8 weeks.
|Table 1: Dietary formulations for the different groups in the study | Kyn, kynurenine; Trp, tryptophan (Dukes. 2015).|
|Figure 1: Body composition (% body fat and % lean mass) of the rodents on the different diets (Dukes. 2015).|
|Without sufficient tryptophan the levels of serotonin (5-HT), growth hormone (GH) and the thyroid hormones TSH, T4 & T3 plummet (Musumeci. 2015).|
Against that background and in view of the fact that tryptophan is also important for the production of 5-HT (serotonin), growth hormone (GH) and the thyroid hormones, TSH, T3 and T4 (Musumeci. 2015), we can still conclude that we're not dealing with completely arbitrary / random results here.
|Figure 2: An anlysis of muscle samples revealed significant increases in the myostatin suppressing protein follistatin, IGF-1 and leptin, as well as slight decreases in myostatin (Dukes. 2015).|
- Dukes, Amy, et al. "The aromatic amino acid tryptophan stimulates skeletal muscle IGF1/p70s6k/mTor signaling in vivo and the expression of myogenic genes in vitro." Nutrition (2015).
- Lin, Frank D., Trevor K. Smith, and Henry S. Bayley. "A role for tryptophan in regulation of protein synthesis in porcine muscle." The Journal of nutrition 118.4 (1988): 445-449.
- Musumeci, Giuseppe, et al. "Importance of serotonin (5-HT) and its precursor l-tryptophan for homeostasis and function of skeletal muscle in rats. A morphological and endocrinological study." Acta histochemica 117.3 (2015): 267-274.
- Sanfilippo, S., R. M. Imbesi, and S. Sanfilippo Jr. "Effects of a tryptophan deficient diet on the morphology of skeletal muscle fibers of the rat. Preliminary observations at neuroendocrinological and submicroscopical levels." Italian journal of anatomy and embryology= Archivio italiano di anatomia ed embriologia 100 (1994): 131-141.