Acute administration of nutritionally sourced tryptophan increases fear recognition.

What Was Tested

The paper reports a study of Tryptophan and Serotonin, published as a randomized controlled trial.

The serotonin precursor tryptophan (TRP) has been widely used as a nutritional supplement and antidepressant.

Recently, however, the use of TRP has been severely restricted due to its association with the eosinophilic myalgic syndrome, an autoimmune disorder probably caused by ingestion of a contaminant produced in certain TRP manufacturing processes.

Who Took Part

The abstract describes 24 subjects taking part.

The age groups tagged for this paper are adults and middle-aged adults, women only.

How the Study Was Run

The design is described as randomized, double-blind, placebo-controlled and parallel-group.

Random assignment meant chance, not the researchers, decided who got Tryptophan and who got the comparison, which limits bias.

Neither the subjects nor the staff measuring them knew who was on Tryptophan, so expectations could not easily colour the readings.

Some subjects received a placebo instead of Tryptophan, giving a reference point.

The Tryptophan group and the comparison group ran side by side rather than switching.

The researchers carried out venous sampling for amino acid and hormone estimation and performed a test of emotional processing using a facial expression recognition task.

What Was Measured

PubMed files the paper under topics including Biological Availability, Diet, Facial Expression, Fear, Human Growth Hormone, Hydrocortisone and Prolactin.

What This Means in Plain Language

The paper is a randomized, double-blind and placebo-controlled study of Tryptophan and Serotonin in 24 subjects.

With fewer than 40 people, it is a small study, so it is better read as an early signal for further research than as a settled answer.

Its findings take up roughly 4 sentences of the abstract and are left out here on purpose; the source paper is the place to read them.

The publication is from 2003 (Psychopharmacology), a journal based in Germany.

More context: all human trials.