Tryptophan: The Trust Supplement?

Trust of a colleague, trust of a business partner, trust of data, trust of your instincts - as the glue that binds our society, trust plays a fundamentally important role in our everyday lives, shaping our perceptions of the world and impacting our relations with others, but have you ever considered that your willingness to trust could be influenced by what you eat?

Every kind of peaceful cooperation among men is primarily based on mutual trust...

Albert Einstein

Providing further evidence of how biological mechanisms might shape our psychology, researchers from the Universities of Leiden and M�nster recently discovered that people?s trust in others increases after intake of the the amino acid tryptophan - found in foods such as fish, soya, eggs and spinach.

Using forty unacquainted healthy adults (mean age = 19.4), twenty participants (2 male, 18 female) were given an 0.8g oral dose (powder) of tryptophan, while another 20 (2 male, 18 female) were given a neutral placebo, dissolved in 200 ml of orange juice.To determine the effect of tryptophan, the researchers gave one group of test persons orange juice with added tryptophan, while a second group was given a placebo with their orange juice.


Subsequently, the test persons played a trust game, a task that is often used to measure how much one test person trusts the other. A trustor was given 5 euros and was free to decide how much of that money he would give to a trustee in each round of the game. The trustor would then receive extra money, but only if the trustee gave him enough money in return. The money transferred to the trustee by the trustor served as an indicator of mutual trust.

Now before you rush off and encourage your team members to gorge on fish, soya, eggs and spinach, bear in mind that previous studies have suggested that it's very difficult to alter blood tryptophan levels through dietary methods alone.

As the authors admit, among other ways that the experiment could have have been swayed, is the possibility that tryptophan might simply make people more trusting by increasing the inclination to take social risks. Trust, after all is always partly a risky endeavour. The gender imbalance in participants might also have been an issue - particularly important given that previous studies suggest that women may be more sensitive than men to changes in serotonin levels (biochemically derived from tryptophan). The authors address this by claiming that the imbalance cannot account for the effect of tryptophan on trust, as the four male participants were evenly distributed across conditions.

A billboard with the sign: "If you can't trust a man's handshake, what good is his signature."

Despite these methodological concerns, the authors are adamant that this study adds to the evidence that "we are what we eat".

The food one eats has a bearing on one?s state of mind. Food can thus act as a cognitive enhancer that modulates the way one thinks and perceives the physical and social world.

Lorenza Colzato

Whether this increased willingness to trust carries over into non-monetary contexts is unclear, but the next time you have difficulties getting colleagues to trust and collaborate with one another, as a last resort you might perhaps want to suggest some tryptophan supplements.

The paper 'Tryptophan Promotes Interpersonal Trust', jointly authored by Lorenza S. Colzato , Laura Steenbergen, Erik W. de Kwaadsteniet, Roberta Sellaro, Roman Liepelt and Bernhard Hommel is published in the Journal of Psychological Science.

Photo: simplerich, Video: Leiden University
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This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.