The Medical Minute: What Makes You Sleepy on Thanksgiving?

Call it the turkey’s revenge.

November 22, 2022Penn State Health News

Every year, millions of Americans enjoy their annual Thanksgiving feast, then sit back to watch a Detroit Lions NFL game or enjoy lively political discussion with their families, but they can’t keep their eyes peeled.

It’s like they’ve been… drugged.

The popular conjecture is that turkey meat contains a high concentration of a naturally occurring chemical called tryptophan that causes you to sleep much of the time you should be spending on gratitude. But Kent Vrana, Elliot S. Vesell professor and chair of pharmacology at Penn State College of Medicine, who has studied the chemical throughout his career, says eating a cheeseburger makes you sleepy just as quickly as a plate of dark or white bird meat.

What is Tryptophan?

With tryptophan, you’re more likely to end up with big biceps than an urge to nap. Tryptophan is one of 20 amino acids, the chemicals the human body uses to make the proteins essential for building muscle. “Ninety-nine point nine percent of the tryptophan we ingest is used to make the structures in our bodies,” Vrana said.

Humans use a small amount of the tryptophan to make chemicals called neurotransmitters that help the cells in their brains communicate with each other. Tryptophan is a precursor to the production of serotonin, the brain’s feel-good hormone whose activity is modulated by many antidepressants. And then an even smaller portion of that serotonin is converted into melatonin, which is a natural sleep aid.

And Turkey is full of them. Right?

“All meat contains tryptophan,” Vrana said. “It’s a myth that turkey contains more.”

In fact, there’s no more tryptophan in your Thanksgiving turkey than in a wild boar roast — even with stuffing and cranberry sauce.

The scientific misunderstanding that led to the idea appears to stem from tryptophan’s serotonin-melatonin-producing properties. But the amounts of these chemicals produced are so small that they won’t knock you out. Yet, like the dinner from which it is derived, the tryptophan turkey story has had legs over the decades. It is a plot point in sitcoms and used during dinner conversations. Even the pharmaceutical industry has occasionally bought in. Decades ago, drug companies began marketing super-high concentrated doses of tryptophan as an over-the-counter pill to help people sleep. It is also a component of some powders that weight lifters use to build muscle.

So Why Do I Get So Dizzy After Thanksgiving Dinner?

“Euphemistically, it’s called postprandial depression,” Vrana said. ‘I’m a carnivore. So if I eat a steak or a really big burger – especially if I have a few beers with it – I get sleepy. But it has nothing to do with tryptophan.”

There could be an evolutionary component at play. Hundreds of thousands of years ago, when the question “What are you thankful for?” prompting answers like “this loincloth” and “I haven’t been eaten by a saber-toothed tiger this year,” our ancestors hunted for their November meals. After eating, their bodies instinctively knew it was time to rest and recover for the next hunt. And maybe play a lion game (which was played by real lions in those days).

“There will be a shift in your blood flow to the gut, because you have a lot of work to do digesting all that stuff,” Vrana said. ‘Theoretically you don’t have any stress. And so it shifts the neuronal signaling of the stress response.”

Your heart rate drops. You feel calm as your body focuses on digestion and getting much-needed rest.

And if you’re lucky enough to sit back in a warm room, surrounded by people you love and reflect on happy times, what could be more soothing?

Or maybe the Detroit Lions are just that bad.

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The Medical Minute is a weekly health news produced by Penn State Health. Articles incorporate the expertise of educators, physicians, and staff and are designed to provide timely, relevant health information of interest to a wide audience.

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The Medical Minute: What Makes You Sleepy on Thanksgiving?

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