Tryptophan: An amino acid for improving sleep, not for physical performance

Tryptophan (abbreviated Trp) is one of the 20 amino acids commonly found in proteins and belongs to the group of indispensable (essential) amino acids, which means that the human body cannot produce it on its own and must obtain it through diet. In the body, tryptophan plays an important role not only as a building block for muscles but primarily as a key precursor to substances affecting our brain and the perception of fatigue. In the world of sports nutrition, it is attributed with effects such as increasing growth hormone release, promoting sleep, reducing pain perception, and enhancing performance. But what of this is true?

Metabolism and role in the body

• Energy metabolism: Tryptophan is an amino acid whose carbon chain can be converted to Acetyl-CoA and acetoacetate, thereby entering the Krebs cycle (TCA cycle) and serving as an energy source.
• Precursor to neurotransmitters: The most important function of tryptophan from a sports science perspective is its role as a precursor for the synthesis of serotonin (5-hydroxytryptamine), a neurotransmitter that regulates sleep, mood, pain perception, and aggression.

Effects on physical performance vs. scientific reality

The main hypothesis attributing a positive effect on physical performance to this amino acid is based on its function as a serotonin precursor, which can delay pain perception and thus improve physical performance.

The results of a study by Segura and Ventura, 1988, suggested that tryptophan could reduce perceived exertion (RPE) and improve endurance by 49%, but these results were later criticized as unrealistic, precisely because of the high values of improvement, which are not realistic. Later, methodologically robust and well-controlled studies on trained runners and cyclists (e.g., Stensrud et al., 1992 or van Hall et al., 1995) did not demonstrate any significant effect of tryptophan on athletic performance.

Although both tryptophan and BCAAs are associated with the hypothesis of reducing central fatigue, high-quality studies, such as Newsholme, Blomstrand, and Ekblom 1992, attribute the opposite effect to it, namely, an increase in fatigue and drowsiness.

L-tryptophan as a sleep aid

As we have already indicated in previous sections of the article, L-tryptophan can be a suitable and effective dietary supplement for promoting sleep (Langan-Evans et al. 2023). The current recommended dosage for sleep support is 1 g of L-tryptophan, which is equivalent to 300 g of turkey meat (Jeukendrup and Gleeson 2025).

Conclusion for athletes

Tryptophan is an essential dietary component with a profound influence on our brain's chemistry. Current scientific evidence does not support its supplementation as a means to directly enhance athletic performance. Its primary benefit thus remains in the area of sleep and mood regulation outside of physical activity itself.

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Sources

1. Segura, R., and J.L. Ventura. 1988. Effect of L-tryptophan supplementation on exercise performance. Int J Sports Med 9:301-305.
2. Stensrud, T., F. Ingjer, H. Holm, and S.B. Strømme. 1992. L-tryptophan supplementation does not improve running performance. Int J Sports Med 13(6):481-485.
3. Jeukendrup, A., & Gleeson, M. (2025). Sport nutrition (4th ed.). Human Kinetics.
4. van Hall, G., J.S.H. Raaymakers, W.H.M. Saris, and A.J.M. Wagenmakers. 1995. Ingestion of branched-chain amino acids and tryptophan during sustained exercise in man: Failure to affect performance. J Physiol 486(3):789-794.
5. Newsholme, E.A., E. Blomstrand, and B. Ekblom. 1992. Physical and mental fatigue: Metabolic mechanisms and importance of plasma amino acids. Brit Med Bull 48(3):477-495.
6. Langan-Evans, C., M.A. Hearris, C. Gallagher, S. Long, C. Thomas, A.D. Moss, W. Cheung, G. Howatson, and J.P. Morton. 2023. Nutritional modulation of sleep latency, duration, and efficiency: A randomized, repeated-measures, double-blind deception study. Med Sci Sports Exerc 55(2):289-300.