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Turkey Night in Canada; Tryptophan makes me sleepy

October 11, 2009









We Canucks have our Thanksgiving a bit earlier than our friends south of the border. Tonight, there was the standard turkey, potatoes, gravy, etc. and our bellies are full of warmth and wine.

Why are we so sleepy after we eat this bountiful meal? *yawn* There are lots of causes of fatigue, but some very specific to turkey day. Some say it is that a large amount of blood diverted to the gut for digestion, relatively reducing the oxygen that reaches our brain, that causes this fatigue. Better explored is this theory:

Turkey contains high amounts of tryptophan (* I’ll address this ‘fact’ later). Tryptophan is an amino acid, and a precursor for serotonin, a neurotransmitter thought to be involved in mood, sleep, appetite, and learning. An increase in tryptophan means an increase in serotonin (1); this and the subsequent production of melatonin – a hormone that helps regulate our body’s clock – is the going explanation for why eating turkey makes us want to head to bed.

A placebo-control study explored objective and subjective measures of fatigue following ingestion of tryptophan; the study, published in Nature, found that both perception and objective measures of fatigue were significantly altered in the test group. The study only had 6 participants, drawing into question its validity and generalizability. However, other data, like rat studies, support the increased tryptophan –> elevated serotonin & melatonin –> central fatigue theory.

In MIT’s Technology Review, they looked at data showing that tryptophan helps sustain trust and cooperation. They also touched on the idea that the turkey isn’t actually the cause of our post-prandial (after meal) fatigue. And this seems to be true. Turkey doesn’t contain much higher levels of tryptophan than do other kinds of meat, and per gram of protein, milk is actually one of the foods that is most rich in this substance (wiki helped me). The large amount of alcohol and carbohydrates that we imbibe along with our turkey dinners is probably the more likely culprit for our fatigue.

Alcohol is a central-nervous system depressant and can be a contributor to dangerous degrees of fatigue. Even if we are sober, we still pack our bellies with lots of starchy goodness over the holidays. Ingestion of carbohydrates triggers the release of insulin, a hormone involved in metabolism. The surge of insulin stimulates our muscles to uptake certain kinds of amino acids with the exclusion of tryptophan, creating a relatively elevated amount of tryptophan in the blood. More tryptophan is then taken up by an amino-acid transporter into the central nervous system, converted into serotonin, melatonin, and voila, zzzzzzzzzzzz! If you are a biochemistry keener, read the Introductory section of this paper.

On that note, I’m off to bed. Enjoy your holiday and please be safe on the roads. Gobble gobble!

From Tryptophan to Serotonin to Melatonin

One Comment leave one →
  1. August 27, 2013 12:07 pm

    Good to know. Thanks for vedy deep post!

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