Two periods compared in the same participants
The trial included 31 healthy adults with an average age of 24 years, 90.3% of whom were women. In a randomized crossover design, each participant completed an eight-week period consuming 40 g of walnuts per day and a period of the same length without nuts. A two-week interval between periods brought the total duration to 18 weeks.
The researchers assessed mood, perceived stress, well-being and food cravings using validated questionnaires. They also measured urinary cortisol, 5-HIAA, a serotonin metabolite, and urolithins produced by the breakdown of compounds in walnuts.
A statistical difference, uncertain practical significance
During the walnut period, the total mood disturbance score was 4.85 points lower than during the control period. This difference was statistically significant, with a p-value of 0.030.
However, the abstract provides neither a confidence interval nor a threshold for assessing the clinical significance of this difference. It also does not report detailed results for all questionnaires. The main finding is therefore not enough to conclude that stress or well-being improved overall.
Urine does not directly reveal what is happening in the brain
Walnut consumption was accompanied by an increase in urinary 5-HIAA and urolithins, with no change in urinary cortisol. Changes in 5-HIAA were associated with changes in fatigue and the overall mood score.
These associations do not prove that the metabolites explain the observed improvement. The authors suggest dietary, microbial or peripheral metabolic responses. An increase in urinary 5-HIAA does not demonstrate an increase in serotonin in the brain.
A signal to confirm, not a prescription
The crossover design allows each person to serve as their own control. But the trial was open-label: participants knew whether they were eating walnuts. This knowledge can influence responses to mood questionnaires.
The small, predominantly female sample also limits generalizability. This trial in healthy people does not establish that walnuts treat a mood disorder and does not, on its own, justify a dietary protocol.
Limitations to keep in mind
PubMed abstract only; full text not consulted. Small, open-label trial in a young, predominantly female population. The clinical significance of the difference is not established in the abstract. Funding, conflicts of interest and tolerability data were not verified.
What we can take away
Walnuts appear to improve a mood score in this small trial. The size of the benefit and its mechanism remain to be confirmed.
Sources and provenance
- Walnut consumption improves mood and is associated with increased urinary excretion of 5-hydroxyindoleacetic acid and urolithins in a randomized crossover trial.
Source date: 2026-10-19.
Journal Article, Randomized Controlled Trial · Résumé PubMed uniquement, texte intégral non consulté