• In a clinical trial with 31 healthy young adults living in Spain (average age 24 years), consumption of 40 grams (approximately one and a half ounces) of walnuts daily was associated with overall improvement in mood, accompanied by a reduction in anger and fatigue.
   
• These findings, together with those of a complementary 2025 study, suggest that walnut consumption may have beneficial effects on different aspects of well-being, such as mood and sleep.
   
• The researchers and registered dietitian-nutritionists Drs. Maria Izquierdo-Pulido, Fernanda Zerón, and Isabella Parilli highlight that incorporating a handful of walnuts a day is a simple gesture within a healthy diet, and that the new findings reinforce the interest in continuing to investigate their role in mood.

FOLSOM, Calif., Oct. 1, 2026 /PRNewswire/ — Clinical research led by Dr. Maria Izquierdo-Pulido, Professor of Nutrition and Food Science at the Torribera Campus of the University of Barcelona, shows that consuming a handful of walnuts a day for eight weeks may help improve mood in healthy young adults.¹ The study, published in Food & Function and supported by the California Walnut Commission, also provides new evidence on the possible biological mechanisms involved, related to the gut microbiota and serotonin metabolism. During the intervention, improvements were also observed in some aspects related to emotional eating, although these findings were exploratory in nature.

These findings add to complementary 2025 research by the same team, in which walnut consumption increased a biomarker of melatonin, a key hormone in sleep regulation, after the intervention period compared to the control period.² Taken together, both studies suggest that regular walnut consumption may have beneficial effects on different dimensions related to well-being, such as mood and sleep, and open new avenues to investigate the role of the gut-brain axis in these effects.

Walnuts and Mood: Key Study Findings

In this 18-week clinical trial, 31 healthy young adults, with a mean age of 24 years, consumed 40 grams (approximately an ounce and a half) of walnuts per day for eight weeks. Compared to the control period, the study found:¹

• A significant reduction in overall mood disturbance.
• Decreases in anger and fatigue levels.
• A reduction in some aspects of emotional eating and food-related guilt.

Improvements in mood were observed after eight weeks of intervention, supporting the potential role of regular walnut consumption as part of a healthy diet.

How Walnuts May Influence Mood: The Gut-Brain Connection

This research advances our understanding of how walnut consumption may influence mood through the connection between the gut microbiota and serotonin metabolism. During the intervention, participants showed significant increases in both urinary levels of urolithins, metabolites derived from walnut polyphenols, and 5-HIAA, the main metabolite of serotonin.¹

To explain these findings, the researchers propose the following mechanisms:

• Walnut ellagitannins and gut microbiota: Walnuts contain a high level of polyphenols, including ellagitannins.³ When consumed, these compounds are metabolized by the gut microbiota.
• Urolithin production: The microbiota transforms ellagitannins into urolithins, bioactive metabolites with antioxidant, anti-inflammatory, and neuroprotective properties that may play a role in gut-brain communication.^1,4
• Relationship with serotonin metabolism: In the study, the increase in urolithins was associated with an increase in urinary 5-HIAA. These results suggest a possible relationship between walnut polyphenol metabolism and serotonin-related pathways, although further studies are still needed to understand the mechanism.

“What is particularly interesting about this study is that we not only observed an improvement in mood but also changes in biomarkers that help us explore the biological mechanisms that may underlie this effect,” explains Dr. Maria Izquierdo-Pulido, lead investigator of the study at the University of Barcelona. “The observed relationship between urolithins and serotonin metabolism opens an interesting avenue for further research into the connection between walnut consumption, gut microbiota, and emotional well-being.”

While the study showed promising results, the population was small and included a mostly female sample. Further research is needed over longer periods of time to confirm these findings and determine whether potential benefits are also observed in other ages, populations, and in people with mood disorders.

Beyond Mood: The Nutritional Profile of Walnuts

Incorporating a standard one ounce of walnuts provides essential nutrients⁵ and is an accessible way to support a healthy diet: 

• Protein: 4g 
• Fiber: 2g
• Tryptophan: 38mg
• An excellent source of plant-based omega-3 ALA: 2.5g* 
• Abundant polyphenols (69.3 ± 16.5 µmol catechin equivalents/g)^6,+ 
• Magnesium: 42.6mg 

Walnuts are a nutrient-dense food that provides protein, fiber, omega-3 fatty acids, minerals, and bioactive compounds. Some of these components, such as tryptophan, ALA, and polyphenols, have been studied for their potential role in processes related to brain function and mood. These findings reinforce interest in including foods such as walnuts within broader nutritional strategies aimed at promoting well-being and brain health.

Easy Ways to Add Walnuts to Your Diet

• At breakfast: Add them to cereals, yogurt, or oatmeal, or incorporate them into homemade bread.
• As a snack: Enjoy a handful between meals.
• In main meals: Add them to salads, pasta, legumes, or Mediterranean-inspired dishes.

“Walnuts are very easy to incorporate into daily eating,” the researchers note. “Our results suggest that a simple habit such as including a handful of walnuts a day could also be of interest in relation to mood, always as part of a healthy eating pattern.”

For recipes, usage ideas and more, visit walnuts.org and follow @cawalnuts.

About the California Walnut Commission

The California Walnut Commission (CWC) represents more than 3,700 California walnut growers and approximately 70 handlers whose walnuts are sold around the world, with more than 99% of the walnuts grown in the United States being from California. California walnuts, grown primarily in multi-generational family orchards, are known for their quality and nutritional and wellness benefits.

The CWC, established in 1987, drives domestic and export market development activities and health research to support sales of California walnuts around the globe.

References:

1. Zeron-Rugerio MF, Parilli I, Gonzalez-Rodriguez A, et al. Walnut consumption improves mood and is associated with urolithin production and serotonin turnover: a randomized crossover trial. Food & Function. 2026; DOI: 10.1039/d6fo00807k
2. Zerón-Rugerio MF, Ibarra-Picón A, Diez-Hernández M, Comas-Basté O, Pérez-Cano FJ, Cambras T, Izquierdo-Pulido M. Daily walnut consumption increases 6-sulfatoxymelatonin urinary levels and can improve sleep quality: a randomized crossover trial. Food Funct. 2025 Sep 15;16(18):7023-7035. doi: 10.1039/d5fo00971e.
3. E. Ros, M. Izquierdo-Pulido and A. Sala-Vila, Curr. Opin. Clin. Nutr. Metab. Care, 2018, 21, 498–504.
4. M. Trapali and V. Lagouri, Open Med. Chem. J., 2025, 19, e18741045375825
5. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019. Fdc.nal.usda.gov.
6. Prior R. Oxygen radical absorbance capacity (ORAC): New horizons in relating dietary antioxidants/bioactives and health benefits. J of Functional Foods. 2015;18(B):797-810

+ The data for antioxidant capacity of foods generated by test-tube methods cannot be extrapolated to human effects. Clinical trials to test benefits of dietary antioxidants have produced mixed results.

*A one-ounce serving provides 18g of total fat, “good fats” including 2.5g of monounsaturated fat and 13g of polyunsaturated fat (of which 2.5 grams is plant-based omega-3 ALA), as well as 1.5g of saturated fat.

View original content to download multimedia:https://www.prnewswire.com/news-releases/daily-walnut-consumption-may-improve-mood-in-young-adults-302896362.html

SOURCE California Walnut Commission