Eating Walnuts Every Day Linked to Better Mood and Serotonin Metabolism Changes: Study - Video

Eating walnuts daily may help improve mood in young adults, while also altering markers linked to serotonin metabolism, according to a new study.

Published in Food & Function, the study examined whether consuming 40 grams of walnuts for eight weeks affected mood, stress and urinary serotonin markers in adults aged 20 to 35.

The trial included 31 participants who completed both periods. About 90% were women. Participants consumed 40 grams of walnuts with dinner for eight weeks or avoided nuts and nut products. After a two-week washout, they switched to the other condition. Both periods followed a Mediterranean-style diet.

Researchers assessed mood using the Profile of Mood States questionnaire, stress, well-being and food cravings. First-morning urine samples were analysed for 5-hydroxyindoleacetic acid (5-HIAA), a metabolite of serotonin, cortisol and gut-derived urolithin A and B.

Walnut consumption was associated with a 4.85-point reduction in total mood disturbance compared with the control condition. Anger and fatigue also initially decreased, but these differences were not statistically significant after correction for multiple comparisons. There were no significant changes in perceived stress, well-being or positive mood measures.

Urinary 5-HIAA increased during walnut consumption, and higher levels were associated with lower total mood disturbance. Urolithin A and B also increased and were associated with concurrent increases in urinary 5-HIAA.

However, the findings do not show that walnuts directly increase serotonin activity in the brain. Urinary 5-HIAA reflects whole-body serotonin metabolism and can be influenced by diet, intestinal metabolism and kidney function.

The study was small, open-label and predominantly involved women, which limits how widely the findings can be applied. Larger and longer studies involving more diverse populations are needed to determine whether walnuts can consistently support mood and to clarify the biological mechanisms involved.

REFERENCE: Zerón-Rugerio, et al.; (2026). Walnut consumption improves mood and is associated with increased urinary excretion of 5-hydroxyindoleacetic acid and urolithins in a randomized crossover trial. Food & Function. DOI: 10.1039/d6fo00807k