Tired? You're not filled with tryptophan, but with food

Somewhere around the late 1990s, blaming tryptophan consumption for post-Thanksgiving lethargy became as much of a holiday tradition as the food itself. This amino acid — present in turkey meat — is supposed to accumulate in your brain, prompting your body to use it to make extra serotonin, a chemical that can make you feel sleepy.

But, as this RiskBites video and a very excellent article by Matt Shipman both explain, there's actually a simpler explanation for the sleepiness you feel after eating two helpings of turkey, trimmings, and pie. Simply put: You ate too damn much.

Many people gorge themselves at the Thanksgiving table. During the resultant digestive process, the body diverts as much as 50 percent of its blood to the small intestine, to maximize absorption of calories and nutrients. That means there is less blood available for physical activity. Furthermore, most traditional Thanksgiving meals are high in fat and protein content, which actually slows down the digestive process. So your body is going to be diverting blood to the small intestine for a longer period of time.

Unfortunately, pointing this out to the family members sprawled on your living room furniture will not make you sound nearly as clever as the tryptophan myth does. And the bit about the blood flow to the intestine might get you (slowly, sluggishly) lynched. Maybe, instead, you can just recommend a nice walk.

Read the rest of Matt Shipman's piece on tryptophan, including an interaction between mashed potatoes and turkey that could, conceivably, cause tryptophan-induced sleepiness.


  1. I’m sure this is true, but I’m also pretty sure the tryptophan myth predates the 1990s by at least a decade.  I can remember reading it in a glossy magazine (People?) in a house I didn’t live in after 1982.

  2. the holiday tradition of Blaming post Thanksgiving Lethargy on Tryptophan has been replaced with the holiday tradition of articles explaining that Triptophans in the Turkey isn’t what makes you drowsy.

  3. Mythbusters also covered it:
    Control, Trytophan tablets, Big Turkey Dinner, Big Dinner with turkey replaced with protien powder, small turkey dinner heavy on the turkey.  Control and Small dinner with lots of turkey == Not Drowsy.  All others == Drowsy.

  4. Another theory is the postprandial alkaline tide:  with food in your stomach, you must increase your H+ production to maintain a low gastric pH.  Every time your parietal cells produce H+ for the stomach, they must also produce an anion that goes somewhere else.

    The anions produced are bicarbonate (HCO3-), and they go to the blood.  This postprandial alkalosis is believed to have inhibitory CNS effects.  (That’s one theory, anyway.)

    IMO, it doesn’t seem accurate to make the link between increased intestinal blood flow and feeling tired.  Intestinal blood flow is increased after a meal, but blood is being shunted from skeletal muscles and peripheral circulation.  The brain is what determines if you are tired or alert, and the brain always gets preferential treatment when it comes to blood flow and nutrients–it will be the last organ to have blood diverted from it.  Furthermore, wakefulness and sleepiness are functions of neurotransmitters like GABA, histamine, and acetylcholine, which are delivered by neurons, not blood (and perhaps bicarb plays a role also).

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