Why does Thanksgiving dinner *really* make you sleepy?

For years, you've heard the tremendous fatigue experienced after an American Thanksgiving dinner laid at the feet of the turkey -- or more precisely, at the tryptophan in that turkey. Trytophan, apparently, is the go-to amino acid for those who want to get sleepy.

But according to an article in the Los Angeles Times, the real story may be more complicated than that:

Turkey does contain a large amino acid called tryptophan. So eating turkey puts some tryptophan into your bloodstream. But there are lots of other large amino acids riding around in there too.

For the tryptophan in turkey to do its sleep-inducing work, it needs an accomplice. Maybe the bread stuffing, the mashed potatoes, those candied yams:

When you eat carbohydrates, the pancreas releases insulin, and one effect of that is to lower the levels of all the large amino acids in your blood -- except for tryptophan. The upshot? You have relatively high levels of tryptophan in your blood, and in your brain that's converted into the neurotransmitter serotonin, and that can make you sleepy.

It seems that the turkey's tryptophan dose is amplified by the sweet and starchy sides. Indeed, perhaps the sides alone would do the job (by clearing out the non-tryptophan amino acids) even if you missed out on the turkey.

(We shouldn't forget, of course, that eating more than you're used to in a sitting -- and giving your system more digestive work to do than it's used to -- might account for a good bit of the fatigue.)

In fact, the article suggests that maybe you'll be even more sleepy if you don't eat your turkey:

[E]ating protein has the opposite effect from eating carbohydrates -- it raises the blood levels of all large amino acids. If all you ate were turkey, you'd have relatively low levels of tryptophan -- and, if anything, you'd have some extra get-up-and-go, instead of all that extra lie-down-and-snooze.

Let's pull back a moment to get clear on the tryptophan theory of needing a nap between dinner and dessert. Is the drowsiness due to the level of tryptophan relative to the other amino acids kicking around in your bloodstream? Or is it due to the the level of tryptophan relative to how much is normally present in your bloodstream?

If the article got the scientific story right, it's the former -- so boosting non-tryptophan large amino acids would counteract the yawns, as would taking in less tryptophan. (I'm guessing maybe the tryptophan-uptake apparatus is sampling from the available large amino acids, which would mean whatever the absolute level of tryptophan coursing through your veins, a high relative level of tryptophan is going to trip the "boy are you sleepy!" circuits more often than not. The brain chemistry mavens are invited to chime in with the relevant facts.)

In any case, this whole discussion seems like a perfect opportunity to conduct some citizen science (and, come Friday, to collect some reports from the field). Ideally, we'd all want to sit down to the same Thanksgiving meal together (having all gotten a good night's sleep the day before, etc., etc.). Sadly, that's not going to happen. However, maybe you can rope those with whom you are dining on Thursday into participating.

Depending on the vibe at your Thanksgiving table, you can either ask the diners to keep track of what kinds of foods they eat, or you can assign your guests particular consumption objectives. Then, before dessert, have everyone do a quick assessment of his or her energy level.

With luck, we'll get data for the following variations:

  • High-tryptophan food (like turkey), high carbohydrate intake. (Prediction: sleepy)
  • High-tryptophan food, low carbohydrate intake. (Prediction: not sleepy)
  • Skip the high-tryptophan food, high carbohydrate intake. (Prediction: sleepy)
  • Skip the high-tryptophan food, low carbohydrate intake. (Prediction: not sleepy)
  • High-tryptophan food, high carbohydrate intake, extra protein. (Prediction: not sleepy)
  • High-tryptophan food, low carbohydrate intake, extra protein. (Prediction: energetic)
  • Skip the high-tryptophan food, high carbohydrate intake, extra protein. (Prediction: not sleepy)
  • Skip the high-tryptophan food, low carbohydrate intake, extra protein. (Prediction: frighteningly energetic)

Of course, if you track participant input a bit more precisely, maybe we'll stumble upon some other factor that turns out to be important, like vitamin A or sage.

See you back here on Friday morning with your results!

Hat-tip: C&ENtral Science.

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I think that the focus on serotonin is wrong. Tryptophan does not easily cross blood-brain barrier. Extra tryptophan will be converted from serotonin to melatonin by the intestine itself. Melatonin easily passes blood-brain barrier and will make you sleepy. There is no demonstration that this is all true, but all the bits and pieces needed for this explanation exist - they just need to be put together and tested as a whole.

Data point from Canadian Thanksgiving (weeks ago...) where half the participants were either vegan or vegeratian.
I didn't eat turkey, but lots of squash and other vegetables, and was really sleepy. People who did eat the turkey were no more or less sleepy than the ones that didn't.

There's also the sensible old argument that after any large meal, your autonomic nervous system is going to divert a higher than usual percentage of blood flow to the GI tract, thus making less available to the CNS, thus inducing a nap.

At any rate, a nap after a good meal *feels* good, so why analyze it? Just take a nap! ;-)

There's also the (red) Burgundy.

By Uncle Fishy (not verified) on 26 Nov 2008 #permalink

You're "sleepy" because you've been getting fucking plastered all day! Sometimes I'll ask PhysioWife in the morning, "What time did we feel asleep last night?" And she says, "I fell asleep. You passed out, you fucking drunk!"

Well, I can help. As a recently diagnosed diabetic, I will be cooking low carb this year. Since I'm also a vegetarian, I expect to have low-tryp foods on the table also (but I will have to check the amino acid profile of wheat and soy proteins to make sure).

By speedwell (not verified) on 26 Nov 2008 #permalink

I don't see why tryptophan would have a particularly difficult time crossing the BBB. It's not all that large, and it's sufficiently hydrophobic, that it should be a cinch.

Wait, are we trying to *not* get sleepy? But the nap is my favorite part of Thanksgiving. And good thing for Speedwell in the comments because I know that I couldn't convince anyone at my house to go with the last option.

I don't see why so much emphasis given here on "relative" levels of tryptophan. Unless the other amino acids interact to modify either the generation rate or effects of tryptamine, the level of the other AAs shouldn't be a big deal, just "tryptophan" by itself.

BTW Coturnix, you may be right but I find it hard to believe that researchers and mfrs. would have let the BBB issue slip by so long. Also, do you know anything about effects of melatonin congeners, such as the 6-methoxy analog etc?

PS: If you want to relax via something other than tryptophan, try "theanine" [sic]. Read up on it. "Suntheanine" producer brand is best.

Relative levels because there's an uptake competition between all them amino acids..

Best as in hoax of the year?
PS: If you need to relax on anything, smoke one o'them...

By rijkswaanvijand (not verified) on 03 Dec 2008 #permalink

Has anyone considered the higher level of CO in the house. Is there any other day of the year the oven is on for @5hrs, doors and windows closed (end of Oct). And a lower level of O2 caused by oven, more people?

By Calvert E. Chesleigh (not verified) on 07 Dec 2008 #permalink