Now to be clear, turkey does contain tryptophan. Tryptophan is an amino acid which the human body doesn’t naturally produce, but is essential to proper body function, and thus must be acquired from food.
The reason tryptophan is tied to drowsiness is that it is used by your body to create serotonin. Serotonin, among other things, acts as a calming agent in the brain and plays a key role in sleep. So with turkey containing tryptophan, one would logically say it would make you sleepy after you eat it… except, this isn’t actually the case.
Tryptophan and Drowsiness
So, why not? Primarily because of how we eat turkey and more importantly how the body deals with tryptophan. If you tend to eat a little turkey on an empty stomach, then there’s a small chance that the tryptophan in the turkey will make you a little drowsy right after you eat it. Add it to a sandwich or have it with some mashed potatoes or any other food eaten at the same time on a non-empty stomach and it won’t be the turkey that is making you drowsy.
It turns out, tryptophan needs to not only be taken on an empty stomach to have any instant effect, but also with little to no other amino acids or protein present in order to make you drowsy after you eat something that contains it. Given that there is a lot of protein in turkey and other amino acids, even if you are a bit malnourished, you are not likely to get drowsy from the tryptophan after you eat turkey, though it will increase your body’s store of the tryptophan.
What’s going on here is that when there are a lot of amino acids around, this causes “competition” among the amino acids as far as crossing the blood-brain barrier. Tryptophan is a particularly bulky amino acid so it ends up being at the back of the line, so to speak, and will generally stay there until those other amino acids are gone or, at the least, until enough of them are gone so the ratio of tryptophan to those other amino acids is drastically increased.
So why do you get drowsy after, for example, eating turkey on Thanksgiving? Well, there are a lot of reasons, but primarily because with your holiday meal you likely just crammed a couple of days worth of food into your body in the span of an hour or so, possibly with some alcohol, which is a central nervous system depressant that has a mild sedative effect. Also, with a full stomach, your body directs blood away from your central nervous system and other organ systems to help with your digestive system. More than anything, this is probably causing most of the drowsiness after a large turkey dinner, such as on Thanksgiving or Christmas etc.
The “drowsy” effect is even more noticeable when your food contains quite a bit of various fats, which take a lot of energy to digest, and carbohydrates. Carbohydrates in particular cause a release of insulin. This results in various amino acids being swept out of your blood, being absorbed into your muscle cells, and thus the tryptophan to other amino acid ratio increases quite a bit, giving the tryptophan a better shot of crossing the blood-brain barrier and raising your serotonin levels.
Now there is typically always a nice store of tryptophan in your body at any given time due to the fact that it is found in higher levels than turkey in chicken, beef, pork, cheese, chicken eggs (which contain nearly four times as much tryptophan per ounce over turkey), sunflower seeds, and many types of fish; it also is found, in lesser amounts as in turkey, in milk, beans, sesame seeds, lamb, wheat flour, chocolate, white rice, oatmeal, potatoes, and bananas, etc. So your body is typically stocked full of tryptophan most of the time and eating some turkey is not going to significantly change your body’s store, though it will add some.
Given that you usually have this large store of tryptophan already in your system, it is unlikely that the small amounts received from a turkey dinner would be the reason you get drowsy. Otherwise, wouldn’t you be drowsy all of the time?
So, if you want to point to a specific food that can make you drowsy, it would be things high in carbohydrates such as pasta, mashed potatoes, breads, etc. (main components of the traditional turkey dinner); these not only cause your body to direct more blood towards your abdomen and away from other organ systems, which will make you drowsy, but also will result in some of the tryptophan hanging out in your body long enough to actually get a chance to make it passed the blood-brain barrier to eventually produce some serotonin.
[Reposted (with editing) from Misconception Junction]