Turkey has got a bit of a reputation for sending people to sleep.
The trouble is, the levels of tryptophan in turkey are comparable to those in other meats.
Do you get sleepy after you eat fried chicken? Or a beef burger? Both contain the same amount of tryptophan as turkey does – about 350 milligrams per 100 gram serving.
"The amount of tryptophan in a single 4-ounce serving of turkey (350 milligrams) is also lower than the amount typically used to induce sleep," write Dr Aaron Carroll and Dr Rachel Vreeman in Don't Swallow Your Gum: And Other Medical Myths Debunked (Penguin, 2009). "The recommendations for tryptophan supplements to help you sleep are 500 to 1,000 milligrams."
So maybe it's just the huge amount of tryptophan you're consuming? Not so fast.
So what is it that induces that post-lunch slump?
This is where things get a little tricky. Because tryptophan does play a part in why carbs make you sleepy.
The short version is: Eating carbohydrates makes more tryptophan available to your brain. The long version, courtesy of Scientific American, goes like this:
Gobbling a slice of sweet pumpkin pie, for instance, causes beta cells in the pancreas to secrete insulin, a hormone that allows the uptake of glucose and most amino acids into the tissues. But insulin has little effect on tryptophan, a large percentage of which travels the bloodstream bound to the protein albumin and therefore is unavailable to the tissues, the notable exception being the brain. By sopping up other amino acids from the blood, however, insulin reduces the tryptophan's competition; the transport system is no longer tied up and more tryptophan can cross the blood–brain barrier.
Carbs lead to insulin, then the insulin helps get rid of glucose and all the other amino acids, leaving tons of tryptophan roaming the bloodstream alone, and eventually crossing into your brain.