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This Is What Actually Makes You Sleepy At Thanksgiving Dinner

You have no-one to blame but yourself. Also, all those carbs you ate.

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Turkey has got a bit of a reputation for sending people to sleep.

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The turkey-makes-you-sleepy myth gets repeated often around the festive season – especially at Thanksgiving in the US. Turkey's supposed sleep-inducing properties were even mentioned in an episode of Seinfeld. But they don't hold up to scientific scrutiny.

"But what about the tryptophan!" you might be thinking.

Turkey contains the amino acid tryptophan, a building block for the hormones serotonin and melatonin, which help regulate sleep. And tryptophan, in pill form, has been shown to ease insomnia.

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."

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So maybe it's just the huge amount of tryptophan you're consuming? Not so fast.

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Now, of COURSE you're going to be eating more than four ounces of turkey during any kind of holiday celebration. So you might think that that means the amount of tryptophan you're eating in all of that turkey is going to make you sleepy, even if a normal four ounce portion wouldn't.

But you'd be wrong.

"In order for L-tryptophan to really make you sleepy, you need to take it on an empty stomach and without ingesting any other types of amino acids or protein," Dr Howard Markel of the University of Michigan told PBS NewsHour.

That pile of turkey you're eating also contains a hefty amount of protein, and that protein is going to get in the way of the tryptophan inducing any of the sleepiness it might on its own.

So what is it that induces that post-lunch slump?

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It's probably the large amount of food in general, and carbohydrates specifically. Not to mention the booze.

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.

So go forth and stuff yourself with food – just don't blame the turkey when you're asleep on the sofa at 5pm.

Kelly Oakes is science editor for BuzzFeed and is based in London.

Contact Kelly Oakes at kelly.oakes@buzzfeed.com.

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