Are you dealing with 'turkey coma'? Why you may feel tired after eating on Thanksgiving

If you're one of the Americans who consumes some of the nearly 46 million turkeys eaten in the U.S. each year on Thanksgiving, you're probably familiar with "turkey coma."

Whether you had just one plate or two, many may experience an overwhelming feeling of drowsiness after the Turkey Day feast that may not seem comparable to any other meal of the year. However, the tired feeling isn't actually just some phenomenon. There's a reason why people are left wanting to get into bed after the grand feast.

You may have always blamed the traditional main dish as the culprit behind the feeling of tiredness, but turkey isn't the sole suspect behind that lethargic feeling, registered dietitian and nutritionist Nancy Farrell Allen says.

"Turkey doesn’t deserve the entire credit for those feelings of drowsiness on Thanksgiving Day," Allen told USA TODAY.

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What is tryptophan?

While Allen says turkey doesn't deserve all the credit for causing drowsiness, there actually is something in the meat that causes a tired reaction.

Turkey contains an amino acid known as tryptophan, which helps the brain release chemicals like serotonin and melatonin. Dr. Donald Hensrud, nutritionist and editor of The Mayo Clinic Diet,told USA TODAY tryptophan is an "essential" amino acid because the human body doesn't produce it.

"There's certain amino acids that we need need to get through our diet, tryptophan is one of them," he said.

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Does tryptophan make people feel sleepy?

The reason why tryptophan makes people feel so sleepy is because of the serotonin and melatonin it produces.

Melatonin is a hormone that regulates someone's sleep cycle, as people can buy over-the-counter dietary supplements of it to help them fall asleep. Serotonin, commonly known as the hormone associated with happiness, has a variety of functions such as stabilizing sleep, mood, appetite and pain, according to the United States Library of Medicine. The mixture of the two hormones is what Hensrud said is the reasoning for feeling drowsy after eating.

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How much is in turkey? Could it really make you tired?

As with all other foods, it all depends on how much turkey one eats on Thanksgiving. Should one person eat 6 ounces of turkey, double the recommended amount suggested by the University of Illinois Extension service, there would be 488 milligrams of tryptophan, Allen said.

However, turkey isn't the only food with tryptophan in it, and other common foods actually have higher levels of the amino acid than turkey.

Other Thanksgiving foods with tryptophan in it include ham, which if eating double the U.S. Department of Agriculture's recommended serving, amounts to 507 milligrams of the amino acid. Chicken, red meat and pork also have tryptophan.

Ever had or been told to have a glass of milk before bed? It's because an 8-ounce-serving of milk has 105 milligrams of tryptophan, which Allen said she recommends to patients to help "elicit a peaceful rest at night." Other dairy products like yogurt and eggs also contain the amino acid.

According to Nutrition Data, turkey ranks 54th of all foods in the amount of tryptophan, behind foods such as eggs, halibut, crab and lobster.

So why do people feel so tired after Thanksgiving dinner?

Allen and Hensrud say there are numerous factors as to why people feel drowsy after a Thanksgiving dinner. While tryptophan can cause sleepiness, Hensrud added that it doesn't act alone.

Whether it is by casserole or it's mashed, potatoes are loaded with carbohydrates, which stimulates insulin production. Hensrud explained that this lowers blood glucose, which promotes the uptake of amino acids, except for tryptophan. Since it's not promoted, there's more tryptophan available to influence someone's tiredness.

Starting the day by not eating breakfast or lunch also doesn't help, as the rapid jump in a large amount of food can be a lot. After all, the average American eats 3,000 calories during the meal.

"Tryptophan works best on an empty stomach," Allen said. "And if you haven’t eaten all day, all this food hits an empty stomach in a short time span."

So regardless of what's on the dinner table, the amount of food people eat really does affect how they feel.

"If people ate a big meal on Thanksgiving, even if it didn't have turkey, they still would feel the same kind of relaxation/drowsiness after eating," Hensrud said.

This article originally appeared on USA TODAY: Does eating turkey make you drowsy? Experts dish on Thanksgiving myth