American black walnuts are different than English walnuts. Black walnuts have a stronger flavor, and grow wild in fields and pastures across the Midwest, and English walnuts come from orchards. Eating walnuts has been associated with better cognitive function, and lower rates of diabetes, depression, and other conditions. Walnuts are high in omega-3s and polyphenols, and black walnuts specifically are high in serotonin. Eating them can increase the principal breakdown product of serotonin, 5-hydroxyindoleacetic acid (5-HIAA), which is generally used to identify serotonin overproduction. Serotonin can be in your food or your body can make it from the amino acid tryptophan. Serotonin is in your brain, but most is in your gut.

The serotonin concentration of black walnuts = 304 mcg/g, and English walnuts = 87 mcg/g. (30 grams of walnuts = 1-ounce serving = ~14 walnut halves/200 calories). Some literature has noted that foods containing serotonin aren’t thought to increase brain levels, but there are very few foods that have serotonin levels as high as black walnuts.

Though it’s a popular myth that eating high-protein foods like turkey will raise brain tryptophan and serotonin levels, it’s not true. There’s too much competition for tryptophan with all the other amino acids in turkey or other meats. Interestingly Acute Tryptophan Depletion (ATD) is a dietary method used in brain research to evaluate the impact of low serotonin levels. It uses a mixture of amino acids without tryptophan, and is associated with a lowered mood, the magnitude of which seems to depend on the baseline state of the subject. This is why I don’t like collagen because it has all the large neutral amino acids, except tryptophan.

Concentrated purified tryptophan or 5-HTP (5-Hydroxytryptophan, a form of serotonin) can increase brain serotonin, and there is some evidence they can be effective in mild-to-moderate depression. (Canada and EU consider tryptophan a drug). 5-HTP is used as a supplement. I have found that people are individual in their response to 5-HTP, some can be impacted by doses as low at 10 mg, while researchers have given 1,000’s of mg in studies. 5-HTP is high in the seeds of Griffonia simplicifolia an African plant that grows black pods. Additionally, butternut or white walnuts are the highest in serotonin with 398 mcg/g, but they are not generally sold in grocery stores.

Tryptophan -> 5-HTP -> serotonin;


  • J Psychiatry Neurosci. 2007 Nov; 32(6): 394–399.
  • Am J Clin Nutr 1985 Oct;42(4):639-43.
  • J Int Soc Sports Nutr 2016 Nov 24;13:43.
  • Food Nutr Res. 2016 Dec 16;60:29272.