Thanksgiving dinner is traditionally followed by the ritual unbuttoning of pants and lounging in a nearly comatose state. One of your random aunts or uncles will point out your drowsy face and remark “oh look, you must have eaten too much turkey!” Wrong, Aunt Trudy! It isn’t exactly the turkey’s fault you want to pass out on the couch.
Yes, turkey does contain tryptophan, an essential amino acid, which can be converted into the neurotransmitter serotonin that is responsible for improving your mood and helping you sleep better. But turkey does not have any more tryptophan than any other poultry. In fact, tofurkey and caribou (Rudolph!) contain much more tryptophan than turkey. What causes the drowsy sensation is actually the accompaniment of carbohydrates in the Thanksgiving meal.
The consumption of carbohydrates triggers the release of insulin (a hormone meant to lower blood sugar levels) which causes the uptake of branched-chain amino acids (BCAA) into muscle, leaving tryptophan (an aromatic amino acid) behind. At the blood-brain barrier, there is a large neutral amino acid transporter which helps both BCAA and tryptophan cross. The now high ratio of tryptophan to BCAA in the bloodstream allows tryptophan to cross the barrier into the cerebrospinal fluid (CF). Once there, the tryptophan can be converted to serotonin. Serotonin can also be converted to melatonin in the pineal gland – a hormone involved in the sleep-wake cycle that chemically causes drowsiness and lowers body temperature. Without the carbohydrates, there ratio of trytophan to BCAA would not be high enough in the blood stream to cause a significant increase in the amounts of serotonin and melatonin in the body. Therefore, turkey is not the lone culprit.
So maybe you shouldn’t be a know-it-all and call Aunt Trudy out at the dinner table for being wrong; but you’ll know it’s the combination of carbs with the turkey, the extreme overconsumption of the turkey+carbs, and the wine that is causing your annual Thanksgiving nap.
Happy Thanksgiving, Premeds! Don’t study too hard.
For More Information:
4. Tryptophan: http://en.wikipedia.org/wiki/Tryptophan
5. Melatonin: http://en.wikipedia.org/wiki/Melatonin#Circadian_rhythm
6. Serotonin: http://en.wikipedia.org/wiki/Serotonin