Tryptophan-enriched diet or 5-hydroxytryptophan supplementation given in a randomized controlled trial impacts social cognition on a neural and behavioral level

V Zamoscik,R Bravo,P Kirsch,S N L Schmidt,A B Rodríguez,T Plieger,M Reuter,L Ugartemendia

doi:10.1038/s41598-021-01164-y

Abstract

Understanding of emotions and intentions are key processes in social cognition at which serotonin is an important neuromodulator. Its precursor is the essential amino acid tryptophan (TRP). Reduced TRP availability leads to weaker impulse control ability and higher aggression, while TRP supplementation promotes confidence. In a double-blind placebo-controlled fMRI study with 77 healthy adults, we investigated the influence of a 4 week TRP enriched diet and an acute 5-hydroxytryptophan (5-HTP) intake on two social-cognitive tasks, a moral evaluation and an emotion recognition task. With 5-HTP, immoral behavior without negative consequences was rated as more reprehensible. Additionally, during story reading, activation in insula and supramarginal gyrus was increased after TRP intake. No significant effects of TRP on emotion recognition were identified for the whole sample. Importantly, emotion recognition ability decreased with age which was for positive emotions compensated by TRP. Since the supramarginal gyrus is associated with empathy, pain and related information integration results could be interpreted as reflecting stricter evaluation of negative behavior due to better integration of information. Improved recognition of positive emotions with TRP in older participants supports the use of a TRP-rich diet to compensate for age related decline in social-cognitive processes.

Highlights

Understanding of emotions and intentions are key processes in social cognition at which serotonin is an important neuromodulator
As serotonin itself cannot cross the blood brain barrier, it is necessary that a sufficient amount of TRP or 5-hydroxytryptophan (5-HTP) is available in the brain. 5-HTP is the direct precursor of serotonin and is almost completely metabolized to serotonin showing a plasma half-life of about 4–6 h6,7. 5-HTP can be found in food, e.g. the bean Griffonia simplicifolia[8], or can be synthesized from TRP by the enzyme tryptophan hydroxylase, which is the initial and rate-limiting step in the synthesis of serotonin
Emotion recognition (RMET) was not related to 5-HTP intake (F1,70 = 0.18, p = 0.670, f = 0.05), but there was a significant effect of the covariate age (F1,70 = 22.12, p < 0.001, f = 0.56; negative association of age with performance; see supplemental Table 2 for results including all covariates and supplemental Table 3 for time effects)

Summary

Introduction

Understanding of emotions and intentions are key processes in social cognition at which serotonin is an important neuromodulator. In a double-blind placebo-controlled fMRI study with 77 healthy adults, we investigated the influence of a 4 week TRP enriched diet and an acute 5-hydroxytryptophan (5-HTP) intake on two social-cognitive tasks, a moral evaluation and an emotion recognition task. Improved recognition of positive emotions with TRP in older participants supports the use of a TRP-rich diet to compensate for age related decline in social-cognitive processes. A major neuromodulator in regulating affective and social-cognitive processes is serotonin[4] the precursor of which is the essential amino acid tryptophan (TRP). TRP depletion leads to lower impulse control ability and higher aggression levels[16] whereas TRP supplementation seems to reduce aggression and to promote prosocial behavior including interpersonal trust and charitable donating[17,18,19]. An important facet of prosocial behavior which is negatively related to aggression and quarrelsomeness is empathy[21]

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Results

Conclusion