A typical Thanksgiving of turkey, football, and sleep

With Thanksgiving in the rear view mirror, some of us are just starting to wake up from our turkey feast-induced coma. Upon waking from my own Rip Van Winkle caliber nap, I began to wonder why exactly the chemical tryptophan, commonly found in turkey meat, was able to put half of America to bed early last night. In the late 1970's researchers hypothesized that normal dietary doses of tryptophan could be used to treat mild insomnia. To test this hypothesis, they gave their subjects a dose of 1 gram of tryptophan, which is on the high side of normal with respect to dietary intake of tyrptophan in a given meal, and they then measured the time it took for the subjects to fall asleep. This time frame is called the sleep latency period. It was seen that in these mildly insomniac patients, the tryptophan helped them fall asleep 15 minutes earlier on average. It was also shown to help to patients stay asleep longer (Hartmann et al., 1979). Yet the question still remaind how exactly tyrptophan accomplished all of this.

 As it turns out, tryptophan is an important ingredient in making some of the hormones that our central nervous system uses to regulate sleep cycles. When tryptophan passes the blood-brain barrier and enters the cerebrospinal fluid surrounding our brains, it gets converted into the chemical signal serotonin. From this stage, serotonin is transported to a different region of the brain where it is converted into the hormone melatonin (Dulce Favacho de Oliveira Torres et. al., 2009). Among many other functions, melatonin is responsible for lowering body temperature and controlling normal sleep cycles, also known as the circadian rhythm. While this cascade explains how thryptophan can lead to drowsiness, that is only half of the story.

Currently, there is an ongoing debate as to whether it is the tryptophan in the turkey or the sheer quantity of food that is consumed during Thanksgiving meals that contributes to the tired feeling. Many scientists, including the Mythbusters, believe that the large portions and all of the carbohydrates in the meals are responsible for making causing the eater to become drowsy. The large amounts of the hormone insulin that are released after a large meal signals muscle cells to begin taking some amino acids out of the blood to be stored for later while allowing other amino acids, tryptophan included, to stay in the blood stream. The increased concentration of tryptophan relative to the amino acids that are taken out of the blood by the muscles allows tryptophan to find free amino acid transporters in the blood-brain barrier more easily (Wurtman et. al, 2003). As a result, more tryptophan is delivered to the brain and more melatonin is made. From these two pathways, it can be concluded that you should pass on seconds of turkey and all of those carbohydrates if you want to be awake to see the end of the night game next Thanksgiving.

References:
Dulce Favacho de, J., & de Souza Pereira, R. (2010, October 6). Which is the best choice for gastroesophageal disorders: Melatonin or proton pump inhibitors? World Journal of Gastrointestinal Pharmacology and Therapeutics, 1(15), 102-106. 

Hartmann, E., & Spinweber, C. L. (1979, August). Sleep induced by L-tryptophan. Effect of dosages within the normal dietary intake. Journal of Nervous and Mental Disorders, 167(8), 497-499.

Wurtman, R. J., Wurthman, J. J., Regan, M. M., McDermott, J. M., Tsay, R. H., & Breu, J. J. (2003,  January). Effects of Normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios. The American Journal of Clinical Nutrition, 77(1), 128-132.