1 Comment »Posted on Thursday 25 December 2008 at 4:24 pm by Jacob Aron
In Biology

I hope you’ve had an enjoyable day so far. By now (if you’re anything like me) you’ve stuffed yourself full of turkey and all the trimmings, and have crawled to the sofa to doze until Doctor Who comes on. Just what is it about a full Christmas dinner that can make you so sleepy?

Gobble gobble. Yum.
Gobble gobble. Yum.

Well, yesterday I decided to find out. Sorry to break the fourth wall of blogging, but as I said I’m currently lying on the sofa. Through the magic of technology, I’m posting from the past. Still, if you’re doing the same and have a laptop perched atop your full belly, perhaps you’ll enjoy a bit of science.

After doing some extensive research (i.e. hitting up Google) I found this article from Scientific American last year. It seems that turkey contains tryptophan, a naturally occurring amino acid that can be used by the body to produce serotonin. This neurotransmitter has been shown to play a role in sleep.

That’s not the whole story, however. Serotonin levels aren’t necessarily boosted by eating turkey, because the bird contains many other amino acids besides tryptophan, which happens to be the least present in each forkful. All these amino acids try to crowd into the brain at once, transported by special proteins across the blood-brain barrier. Poor little tryptophan can’t even get a look in.

It’s suggested that dessert is the real sleepy culprit, as the sugar in such treats causes insulin to be produced in order to allow the absorption of amino acids. Tryptophan is unaffected by insulin however, allowing it to slip more easier into the brain and start the production of serotonin.

Thing is, (and before I get angry comments, I know that personal anecdotes are not very scientific!) in my house we’re normally so stuffed that we forgo dessert until much later in the day. I’m still very sleepy, however. What gives?

It could simply be the sheer volume of food ingested. It has been suggested that a stretching of the small intestine and a stomach full of fat and protein both can cause sleepiness. Also, with more blood rushing to you digestive system to fuel the work there, less is available for the muscles and brain to keep you active.

Finally, there’s one more culprit: alcohol. I won’t say no to a few drinks with Christmas dinner, and after a bit of tipple it’s very easy to lean back into a comfy chair and fall asleep. So, have another drink, relax, and enjoy the rest of your day!


  1. One Comment

  2. My hypothesis is that your last paragraph explains the entire phenomenon. But, consistent with good scientific practice,I’m prepared to spend the rest of the day trying to falsify it.

    Merry Xmas

    By Tim Jones on Thursday 25 December, 2008 at 8:51 pm

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