Walnut consumption improves mood and is associated with increased urinary excretion of 5-hydroxyindoleacetic acid and urolithins in a randomized crossover trial.
María Fernanda Zerón-Rugerio, Isabella Parilli-Moser, Arnau Gonzalez-Rodriguez et al.
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In 30 seconds
This 18-week open-label randomized crossover trial assessed whether daily walnut consumption affected mood and urinary metabolites in 31 healthy young adults. Participants consumed 40 g of walnuts daily for 8 weeks and completed an equal-length nut-free control period, separated by a 2-week washout. Compared with control, walnut consumption reduced total mood disturbance by -4.85 points (p = 0.030) and increased urinary 5-HIAA and urolithin levels, without changing urinary cortisol. Changes in 5-HIAA were associated with changes in fatigue and total mood disturbance; the study did not establish a mechanism.
Key findings
- Total mood disturbance was lower during the walnut intervention than control (-4.85 points, p = 0.030).
- Urinary 5-HIAA and urolithin levels increased during walnut consumption; urinary cortisol did not change.
- Increases in urinary 5-HIAA correlated with reductions in fatigue (r = -0.392, p = 0.031) and total mood disturbance (r = -0.362, p = 0.049).
- Urinary urolithin changes correlated with concurrent 5-HIAA changes (r = 0.537 and r = 0.634, respectively).
Why it matters
The findings suggest that a whole-food dietary intervention may influence self-reported mood in healthy young adults, alongside changes in urinary metabolites. The associations between metabolite changes and mood outcomes are of mechanistic interest, but do not show that these metabolites caused the mood changes. The results add preliminary human evidence to research on diet and mental health.
What to keep in mind
The trial was open-label and included only 31 healthy young adults, 90.3% of whom were female. The authors state that the proposed mechanistic pathways require further investigation.