Tryptophan is an amino acid and a component of the proteins you eat and the proteins in your body. Because you use tryptophan to synthesize the neurotransmitter serotonin--involved in feelings of relaxation and well-being--you may experience a feeling of sedation or sleepiness after consuming tryptophan.
Tryptophan
Tryptophan is one of 20 common amino acids that are the building blocks of protein. When you consume protein, your digestive enzymes break it into its constituent amino acids and your small intestine absorbs them. Your cells then use the amino acids--tryptophan included--to generate energy and build cellular proteins. You can also use tryptophan for some unique purposes that you can't use the other amino acids for, however.
Serotonin Synthesis
One of the most important physiological applications unique to tryptophan is that you use it to produce serotonin, which is a neurotransmitter. Neurotransmitters are small molecules that help brain cells communicate with one another; serotonin plays many roles in the nervous system, but generally speaking, promotes relaxation and feelings of well-being, explains Dr. Neil Carlson in his book "Foundations of Physiological Psychology." Serotonin can also make you feel sleepy.
Tryptophan and Tiredness
Though the idea of the "Thanksgiving Day coma" being due to tryptophan in turkey has more or less been dismissed as a myth, there's nevertheless some evidence to suggest that consuming large quantities of tryptophan can make you feel tired. Research published in 1982 in the "Journal of Psychiatric Research" by Dr. E. Hartmann suggests that this effect is most pronounced in insomniac patients; those able to sleep normally don't seem to respond significantly to tryptophan.
Considerations
Though serotonin and tryptophan both appear to be able to make you sleepy, research suggests that strangely, it's not due to serotonin production that tryptophan exerts its effect. A 1970 article published in "The Lancet" by Dr. R. Wyatt and colleagues notes that the sleep patterns exhibited by patients given tryptophan don't mirror those expected if they had been administered serotonin. As such, tryptophan appears to induce sleep through a different, non-serotonin-related mechanism.
References
- "Foundations of Physiological Psychology"; Neil Carlson, Ph.D.; 2004
- "Journal of Psychiatric Research"; Effects of Image -tryptophan on sleepiness and on sleep; E. Hartmann; 1982
- "The Lancet"; Effects of L-Tryptophan On Human Sleep; R. Wyatt; 1970
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