What is Tryptophan? - Structure, Sources & Side Effects

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

What is tryptophan? Is it really responsible for post-Thanksgiving meal drowsiness? Read more to learn about its structure, where it comes from, and how it affects your body.

What is Tryptophan?

You probably hear about tryptophan most around Thanksgiving time -- as the story goes, tryptophan in the turkey is usually to blame for making you feel so sleepy after dinner. But there's more to the story, so let's take a closer look into what tryptophan actually is and how it works.

Tryptophan is an amino acid that is critical to our body functioning properly. However, our body doesn't naturally make tryptophan on its own, so it is what we call an essential amino acid, meaning we have to acquire it through our food. Then our body can use it to build proteins that help cellular processes take place.

Tryptophan Structure & Function

The official makeup of tryptophan is (2S)-2-amino-3-(1H-indol-3-yl) propanoic acid (image below). So we know what it looks like, but what does it do? Well, as an amino acid, tryptophan is needed for protein synthesis; specifically, tryptophan helps with the production of serotonin, niacin, and auxin. When the body doesn't get enough tryptophan, it can't make serotonin, which leads to increased feelings of depression.

The molecular composition of tryptophan.
tryptophan structure

Sources of Tryptophan

In addition to turkey, which foods contain tryptophan? Well, there are quite a few foods that have even more tryptophan than turkey, so let's list a couple: eggs, spirulina, soybeans, certain types of cheeses, pork, chicken, beef, oats, salmon, and many, many more. Egg whites have the most tryptophan of any food, but spirulina comes in a close second.

So why does turkey get so much blame for post-Thanksgiving sleepiness? It actually has no more tryptophan than any of the other meats listed above, so that after-meal slump is more likely due to the vast amount of food consumed during large meals like Thanksgiving, as well as the increased amount of carbohydrate consumption. This increase in carbohydrates in the body indirectly leads to the production of sleep-promoting melatonin. Thus, while turkey does have tryptophan, those poor birds are taking a lot of flak for something that isn't all their fault!

Side Effects of Too Much (or Too Little) Tryptophan

If the body doesn't create enough tryptophan by itself, there are supplements that can be used. Tryptophan can be used to treat insomnia, sleep apnea, depression, anxiety, teeth grinding, attention deficit hyperactivity disorder, and Tourette's syndrome, among other things.

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