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The Truth Behind Tryptophan and Thanksgiving

The truth behind tryptophan and Thanksgiving sleepiness. It’s not what you might think that causes tiredness after eating a large Thanksgiving meal.

Turkey, Tryptophan, and Thanksgiving Sleepiness


See this little guy? This is the amino acid tryptophan. Tryptophan helps promotes serotonin and melotonin synthesis in the body. Tryptophan is found in turkey and is blamed for Thanksgiving Day sleepiness.

It’s no secret that a big meal on Thanksgiving leads to feeling tired and lethargic. The myth is blamed on the turkey. Particularly an amino acid in turkey called tryptophan. Tryptophan is an essential protein – meaning we need it in our bodies for the synthesis of hormones and vitamins.  Turkey is one of the first things that comes to mind when foods that contain tryptophan are brought up, mostly because of the way it makes us feel tired after a big Thanksgiving meal. However, it’s not necessarily the tryptophan that’s responsible.

Does Tryptophan Cause Sleepiness?

One of the hormones that tryptophan helps to form is serotonin. Serotonin is responsible for stable moods and healthy sleep patterns. Serotonin is also a precursor to another hormone called melotonin. Melatonin is responsible for healthy sleep cycles (1,2). The big Turkey Day meal is often blamed on the tryptophan that triggers  food induced coma but the truth is, it’s likely the large abundance of carbohydrates that you’re eating that are to blame more than the tryptophan.

Think of an average Thanksgiving meal. Aside from generous portions of proteins there is also an abundance of carbohydrates – breads, pies, potatoes, dressing, fruit salad, etc. Studies show that large carbohydrate meals alter the way tryptophan is absorbed in our bodies.

Here’s what happens to tryptophan in our bodies after a large carbohydrate meal:

  • The consumption of large amounts of carbohydrates causes the pancreas to release large amounts of insulin to process the amounts of sugar in our blood (4).
  • Insulin causes proteins to be absorbed into our muscles, however, certain proteins get absorbed more readily than tryptophan.  So the levels of tryptophan rise in our blood because they’re not being absorbed into our muscles. (8,9).
  • Tryptophan passes into the brain where it’s converted into serotonin (8,9).
  • We feel tired.

The feeling of Thanksgiving Day sleepiness is all thanks in part to a large release of insulin from an over-consumption of carbohydrates.  Unfortunately, turkey gets the bad rap.  Below is a list of common foods and the percentage of tryptophan in relation to available protein.

Food Percentage of tryptophan in available protein (%):
Turkey 1.11
Chicken 1.14
Beef 1.12
Oats 1.39
Eggs 1.33
Sesame Seed 2.17
Milk 2.34

As you can see, turkey isn’t necessarily the food with the highest concentrations of tryptophan.  Milk has substantially more.  Beef and chicken have  similar amounts.  Yet it’s always Turkey on Thanksgiving that tends to get the blame.  The reason that tryptophan has such a large effect is because of the amount of carbohydrates eaten with it.

What you should also know about tryptophan:

  • The type of carbohydrates eaten changes the way tryptophan is absorbed.  The more refined the sugars – the higher the concentration of blood levels of tryptophan (5,7).

Tryptophan doesn’t always cause sleepiness:

Changing the type of meal you eat can effect the way you feel after it.  One study looked at high carbohydrate breakfasts vs. high protein breakfasts and found that the high carbohydrate breakfast caused higher tryptophan concentrations in the blood leading to serotonin synthesis in the body and increased sleepiness(6).

Other Reasons For Thanksgiving Sleepiness Besides Turkey

Okay so maybe it’s not necessarily the Turkey, but maybe it’s some of these things too:

  • The wine.
  • Blame it on the family – yeah we know that’s tiring, and it’s probably been a long day.
  • Blood flow is diverted to the digestive tract to help with digestion, taking blood away from other areas.

So what can you do?  Eat up more protein and less of the carbs if you don’t want to feel sleepy.  Or if you need some post-meal simulation, schedule a Black Friday outing. Enjoy!


1. N.a. “Tryptophan.” Medline Plus. U.S. National Library of Medicine. 9 May 2014. Web. 28 October 2015.
2. Belitz, H.-D., Grosch, W., Schieberle, P. Food Chemistry. Berlin: Springer-Verlag. 2009. 30. Print.
3. N.a. “Tryptophan.” United States Department of Agriculture. National Nutrient for Standard Reference Release. Web. 28 October 2015.
4. Fernstrom, J., Wurtman, R. “Brain Serotonin Content: Increase Following Ingestion Of Carbohydrate Diet.” Science. 3 December 1971. Web. 28 October 2015.
5.  Lyons, P., Truswell, P. “Serotonin Precursor Influenced by Type Of Carbohydrate Meal In Healthy Adults.” The American Journal of Clinical Nutrition. 1988. Web. 28 October 2015.
6.  Breu, J., McDermott, J., Regan, M., Wurtman, J., Wurtman, R. “Effects Of Normal Meals Rich In Carbohydrates Or Proteins On Plasma Tryptophan and Tyrosine Ratios.” The American Journal of Clinical Nutrition. January 2003. Web. 28 October 2015.
7. Afaghi, A., Chow, C., O’Connor, H. “High Glycemic Index Carbohydrate Meals Shorten Sleep Onset.” The American Journal of Clinical Nutrition.” February 2007. Web. 28 October 2015.
8. Oldendorf, W., Pardridge, W. “Kinetic Analysis of Blood Brain Barrier Transport of Amino Acids.” National Center for Biotechnology Information. 5 August 1975. Web. 28 October 2015.
9. Glaeser, B., Maher, T. Wurtman, R. “Diurnal Variations In Plasma Concentrations Of Basic and Neutral Amino Acids In Red Cell Concentrations Of Aspartate and Glutamate: Effects Of Dietary Protein Intake.” American Journal of Clinical Nutrition. May 1984. Web. 28 October 2015.


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