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Turkey's Tryptophan Makes Serotonin

People often associate tryptophan with turkey meat. It is thought by some to be the substance in turkey that makes diners sleepy after consuming a large meal. It is true that turkey does contain this essential amino acid. Nevertheless, it is also found in a wide variety of meat and fish, as well as soy beans.1

Image of chemical makeup of tryptophan

Tryptophan is called an essential amino acid because it not a substance that the body can produce on its own, but must be gotten from the diet2. It is the largest of the amino acids3. It helps manufacture proteins for the body. Tryptophan makes vitamin B3 when the body does not get sufficient amounts in the diet. But its main benefit is that it is used to make serotonin. Serotonin among other things has the effect of producing a feeling of calm and relaxation4. It functions as a neurotransmitter between nerve cells5.

In spite of this effect, nutritionists now believe that the tryptophan in turkey is not what causes the common sleepy feeling after thanksgiving dinner. Rather the sleepiness is the result of so much food being ingested that blood flow is diverted from the brain to the stomach to handle the digestion process.

Tryptophan can be taken as a supplement. Because serotonin will not pass through the blood/brain barrier, there is no positive effect of injecting it into the bloodstream. However, tryptophan does pass through this barrier. Thus many believe that supplementation of tryptophan could help those with a serotonin deficiency. Serotonin has also been found to affect the brain's perception of hunger. Low levels of serotonin make the body crave food. So taking tryptophan may also help reduce hunger cravings for those on a diet.6

Serotonin is the precursor for melatonin, which is vital for sleep. So tryptophan, in the past, has been taken as a sleep aid. 5-hydroxytryptophan, also called 5-HTP, is an intermediate level between tryptophan and serotonin. Therefore it is often used in its place as a supplement.

At one time there was a problem with a supplement made in Japan that included L-5-hydroxytryptophan. Because it was not properly processed, the supplement may have caused eosinophilia myalgia syndrome among some consumers7. Even so, tryptophan itself was not tied to the disease. The flaw was in the fermentation process used by the manufacturer. Tryptophan is generally considered safe to consume. The U.S. Food and Drug Administration at its website states:

Although FDA continues to enunciate its concern about the safety of dietary supplements containing L-tryptophan and related compounds such as L-5-hydroxytryptophan, this does not mean that FDA prohibits the marketing of dietary supplements that contain L-tryptophan. Under the Food, Drug and Cosmetic Act (the Act), as amended by the Dietary Supplement Health and Education Act of 1994 (DSHEA), the manufacturer is responsible for ensuring that its products are safe8.

  1. WHFoods on Tryptophan
  2. National Library of Medicine
  3. University of Arizona on Tryptophan
  4. Psychological Effects of Tryptophan
  5. Lack of Serotonin Linked to Impulsiveness
  6. Ref to: http://www.acdlabs.com/publish/tryptophan/supplement.html - Tryptophan as a dietary supplement
  7. Ref to: http://www.cfsan.fda.gov/~dms/ds-tryp1.html
  8. Ibid.


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