Does eating turkey really make you sleepy?

After a big Thanksgiving feast complete with a roasted turkey dinner and all the classic side dishes, you've probably heard a relative or two start talking about how all of the tryptophan in the turkey is making everyone sleepy. But it turns out that we can't lay all the blame on the tryptophan, and the real truth of why we get sleepy after eating turkey on Thanksgiving is a bit more complicated. 

Let's talk tryptophan. Tryptophan is an amino acid that's found in a lot of different foods, like turkey, meat, chocolate, dairy, eggs, and more (cheddar cheese is actually more tryptophan-rich than turkey). It's one of the building blocks for the hormone serotonin, which regulates sleep (via Scientific American). 

Eating tryptophan-laden turkey on its own isn't enough to make you tired, though, because your body processes it with other, more abundant amino acids that have an easier path to your brain. It's only when you add carbohydrates to the meal that things start to get interesting. The starchy sides and sweet desserts we eat with turkey on Thanksgiving boost insulin production. That insulin absorbs some of the amino acids in turkey, but not tryptophan, meaning that tryptophan has a better chance of reaching your brain and helping to produce serotonin, which can then be synthesized into melatonin to make you sleepy (via Live Science). 

There are plenty of other reasons why you might feel sleepy after eating turkey at Thanksgiving. Eating a big meal containing lots of protein and fat can make you sleepy; the fact that when you digest a big meal the blood rushes to your abdomen which can cause fatigue in your brain and muscles leading to sleepiness; the fact that the human body is designed to operate in a "rest and digest" manner that causes your heart rate and blood pressure to slow down after eating while saliva and gastric activity increase; and the fact that a lot of people drink alcohol with their meal, which is a central nervous system depressant (via Mental Floss) — none of which all be attributed solely to turkey and its tryptophan.

Now just make sure you memorize all this so you can tell your relatives the truth about Thanksgiving turkey during your next family feast.