Question of the Week

What is tryptophan? Does eating turkey really make you sleepy?

Sun, 14th Dec 2008

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Rick Shepp asked:

What is tryptophan? Does eating turkey really make you sleepy?



We put this to John Fry, consultant in food science, nutrition and dietetics.

Roast TurkeyThere's been a question about sleepiness caused by tryptophan in turkey and this is a popular myth in the United States that a feeling of sleepiness arises after the Thanksgiving meal and it's caused by the Thanksgiving turkey having a high content of a substance called tryptophan. Tryptophan is an amino acid, one of the building blocks of protein which means that pretty much all proteins contain some Tryptophan but turkey's not unusual in its tryptophan content. It has about the same amount as chicken or beef. Tryptophan is involved in the desire to sleep after a heavy meal but only indirectly. The root cause of the drowsiness but only indirectly. The root cause is the large carbohydrate intake that usually accompanies a celebratory festive meal. All those roast potatoes, the stuffing, not to mention sugar-rich puddings. They all result in a burst of insulin in the blood stream as the body tries to cope with this influx of sugars. One of the side-effects of this secretion of insulin is that tryptophan gets into the brain more easily and once there part of the tryptophan is transformed into a substance that's called melatonin. Melatonin is a hormone involved in sleep regulation and it can encourage sleep. But really it's the carbohydrate in a heavy meal that triggers drowsiness and tryptophan is just a bit player in the biochemical consequences of over-indulgence in carbohydrates.


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Tryptophan is an amino acid, a building block of protein, although what it has to do with turkey I haven't a clue!

Chris chris, Tue, 9th Dec 2008

Association being mistaken for a causal relationship ...

RD, Wed, 10th Dec 2008

I think RD pretty much has it.  In addition, L-Tryptophan used to be marketed in the US as a dietary supplement to promote (among other things) sleep.  After an outbreak of eosinophilia-myalgia syndrome related to the supplement, the FDA banned its sale in 1989, but overturned the ban in 2001.  I'm not sure what its supplement status is elsewhere in the world. jpetruccelli, Wed, 10th Dec 2008

And so goes any lingering awkward silences over the Christmas Dinner table! scigirence, Thu, 11th Dec 2008

"Cheddar cheese, gram for gram, has more. While cheddar isn't the most exciting cheese in the cheese cellar, no one connects it with sleep."

everything I've read about cheese and sleep talks about how cheese makes you dream more vividly. I don't know how true it is.. but the connection is starting to form in my head... JnA, Thu, 11th Dec 2008

Researchers have shown that people put on tryptophan-deficient diets get depressed. This is because tryptophan is an essential amino acid, meaning that it cannot be made in the body, and is also the precursor of 5HT (5-hydroxytryptamine or serotonin), the brain's feel-good chemical.

So self-inflicted depression is feasible, by eschewing trytophan in food.

Chris chris, Fri, 12th Dec 2008

So is that why when I'm feeling a bit down mac and cheese always makes me feel better? If not please don't tell me 'cos I like the idea of having to eat loads of the stuff for the good of my mental health, and forget the diet! srobert, Wed, 17th Dec 2008

Maybe part of the satisfaction that accompanies consumption of said junk food might be relief at the fact that you've survived the experience without developing BSE, salmonella or cholesterol poisoning...

C chris, Wed, 17th Dec 2008

Possibly due to positive associations with McDonald's, e.g. childhood birthday parties at McD's.

alternatively some allege that there are addictive ingredients in McDonald's burgers,
if so addicts would feel better immediately after their fix.

] RD, Wed, 17th Dec 2008

Well, 'wild turkey' might get you sleepy.
But that you don't eat, more like ahh.
Let me put it this way:)
'gulp gulp gulp'
Aahhhhhhh:) yor_on, Fri, 26th Dec 2008

In my experience, eating beans induces drowsiness, as does eating yogurt, Eating both together affects me powerfully, I can hardly keep my eyes open. Atomic-S, Mon, 26th Jan 2009

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