After Thanksgiving dinner my grandpa sits on the couch and tells me that the tryptophan is starting to kick in. As he takes a nap for the next hour or so I become curious as to what really makes us tired after a Thanksgiving meal.
What exactly does tryptophan do to the body? L-Tryptophan is an essential amino acid found in many foods such as chicken, eggs, cheese, meat, fish, and, of course, turkey. In the brain tryptophan is converted into serotonin which is then converted to melatonin in the pineal gland. Serotonin and melatonin have both been shown to regulate mood, relaxation, and the sleep wake cycles in the brain. A large portion of tryptophan is also absorbed in the blood and delivered to the muscles and other parts of the body for protein synthesis.
While it is true that tryptophan can affect levels of serotonin and melatonin in the brain, scientists believe that tryptophan is not the reason for post-Thanksgiving meal drowsiness. To begin, turkey doesn’t contain any more tryptophan that other types of poultry or fish. Three ounces of tuna contains 240mg of tryptophan while three ounces of turkey only contains 160mg of tryptophan and tuna isn’t thought to cause drowsiness like turkey is. So if it’s not an increased amount of tryptophan making my grandpa dead to the world, what is?
The major culprit for lethargic feelings after Thanksgiving dinner is high levels of carbohydrate intake and, more importantly, an overall increase in food consumption. With the breakdown of carbohydrates and the increased levels of glucose in the blood the pancreas secrets insulin. Along with the uptake of glucose into cells, insulin also triggers cells to take up more amino acids. This is thought to increase the relative concentration of tryptophan available to cross the blood brain barrier and be converted into serotonin. This increase in the relative concentration of tryptophan may cause a slight increase in serotonin, but not enough to cause the tiredness experience after Thanksgiving dinner. The main reason for sleepiness after such a large meal is increased actions of the parasympathetic nervous system. Scientists believe that eating so much for Thanksgiving requires a large amount of energy for digestion and absorption and this expenditure of so much energy is the main cause of tiredness. There is also some evidence showing that less blood is pumped to the brain because it is being shunted to the GI tract which causes some drowsiness.
I came to the conclusion that the main reason for getting so tired after Thanksgiving dinner is not from tryptophan, but from over eating and the large amount of energy required to digest and absorb such a large meal.
Hope everyone enjoyed their Thanksgiving Day dinner and had a great nap after it.
References:
[1] A. M. Helmenstine, Ph.D. Does Eating Turkey Make You Sleepy? Tryptophan &Carbohydrate Chemistry. http://chemistry.about.com/od/holidaysseasons/ a/tiredturkey.htm.[2] L. Zamosky and L. Chang, M.D. The Truth About Tryptophan Does tryptophan reallymake you sleepy -- and is turkey to blame? http://www.webmd.com/food-recipes/features/the-truth-about-tryptophan.
[3] M. Shipman. Thanksgiving Science: Tryptophacts and Tryptophantisies. http://web.ncsu.edu/abstract/science/turkey-day. © 2010
[4] B. Best. Chapter 10: Brain Neurotransmitters.http://www.benbest.com/science/anatmind/anatmd10.html#serotonin.
Unbutton pant syndrome (UPS) seems to be an epidemic around this holiday and this time of year in general. The consumption of large meals leads to a lazy atmosphere that is specifically connected to Thanksgiving and other gorging holidays. Tryptophan certainly used to be the culprit for this holiday fatigue but as AlexS618 hypothesized, this culprit has been proven incorrect. There are other biological factors that are in play, leading to this fatigue after meals. A study about sea Otters shows that Specific Dynamic Action (SDA), leads to an increased metabolism after eating claims or squid (Costa et al. 1984). What the experiment discovered was that the volume of O2 was 54% higher after consuming 0.84 Kg of squid or claims then it is during post absorptive levels. This means that the body metabolizes at a much higher rate after consuming big meals. The reason this is the case is because the body is trying to synthesize proteins and utilize the energy content from the food. The experiment with the sea Otters actually showed that the animal used 10.0%-13.2% of the ingested food energy to digest the food and make use of it (costa et al.1984). The reason we struggle staying awake after feasting during Thanksgiving compared to normal meals is that the meal is so much larger. As seen in a study from Herpetologica the South American Rattle Snake shows a positive correlation between volume of O2 and the size of its meal, meaning the bigger the meal the bigger the metabolic rate (Andrade et al. 1997). But another paradigm exists for individuals like me, where when I gorge myself I do not feel the same Specific Dynamic Action response because I am a vegetarian. A study from the Journal of Fish Biology saw that SDA in Pleuronectes platessa was higher when consuming high protein diets (Jobling et al 2006). So if you are going to eat a lot of Turkey meat at thanksgiving you are also probably going to be unbuttoning your pants while you watch the big game on Thanksgiving Day.
ReplyDeleteM. Jobling, and P Spencer Davies (2006). Effects of feeding on metabolic rate, and the Specific Dynamic Action in plaice, Pleuronectes platessa L. Journal of Fish Biology
Volume 16, Issue 6, pages 629–638
Daniel P. Costa and Gerald L. Kooyman (1984). Contribution of Specific Dynamic Action to Heat Balance and Thermoregulation in the Sea Otter Enhydra lutris. Physiological Zoology. Vol. 57, No. 2, pp. 199-203
Denis V. Andrade, Ariovaldo P. Cruz-Neto and Augusto S. Abe(1997). Meal Size and Specific Dynamic Action in the Rattlesnake Crotalus durissus (Serpentes: Viperidae). Herpetologica. Vol. 53, No. 4 (Dec., 1997), pp. 485-493