Can Daily Walnut Consumption Actually Improve Your Mood?

Walnuts are widely recognized as a healthy food choice due to their rich profile of fatty acids, fiber, and antioxidants. While previous studies have highlighted their potential benefits for heart and brain health, new research published in the scientific journal Food & Function points to yet another advantage: a potential improvement in mood.

The study found that young adults who consumed 40 grams of walnuts daily for eight weeks showed a moderate improvement in their overall mood disturbance score. Researchers also identified changes in substances related to serotonin metabolism and gut microbiome activity. However, this was a small-scale study, and the findings do not definitively prove that eating walnuts directly enhances mental health.

What Makes Walnuts Impact Mood?

Walnuts contain several key nutrients that may be linked to brain function and mental well-being, including omega-3 fatty acids, tryptophan, dietary fiber, and polyphenols—plant compounds with antioxidant properties.

Tryptophan is an amino acid that the body uses to produce serotonin, a neurotransmitter involved in regulating mood, among other functions. Additionally, gut bacteria break down specific compounds found in walnuts to produce substances called urolithins, which may be associated with various biological processes in the body.

The researchers set out to investigate whether daily walnut consumption could influence mood and whether a connection exists between emotional shifts, gut bacteria activity, and serotonin metabolism. The study involved 31 healthy young adults aged 20 to 35, with an average age of 24. Approximately 90% of the participants were women.

A Moderate Improvement in Mood

For eight weeks, participants consumed 40 grams of walnuts daily alongside dinner. During another eight-week period, they completely avoided eating nuts and products containing them. A two-week washout period separated the two phases, ensuring every participant experienced both conditions.

Researchers evaluated participants' mood, stress levels, psychological well-being, and food cravings. Concurrently, urine samples were tested for cortisol levels, gut-bacteria-derived metabolites, and 5-HIAA, the primary breakdown product of serotonin.

After eight weeks of walnut consumption, the total score on the mood disturbance index was 4.85 points lower compared to the period when participants avoided nuts. In this index, a lower score indicates a better mood.

Initially, researchers also noted a decrease in feelings of anger and fatigue, but these changes lost statistical significance after adjustments. Other metrics, including stress, psychological well-being, vitality, and positive mood, showed no significant differences.

The Biological Explanation

One of the most intriguing findings relates to serotonin, a substance involved in regulating mood, sleep, and appetite. During the walnut-eating period, a significant increase was recorded in urinary 5-HIAA levels, a byproduct of serotonin breakdown. Researchers also found a correlation between higher levels of this substance and lower scores on the mood disturbance index.

Simultaneously, levels of two additional compounds—urolithin A and urolithin B, produced by gut bacteria breaking down plant components—increased. This rise was likewise linked to higher 5-HIAA levels.

While these findings suggest a connection between walnut consumption, gut microbial activity, and serotonin metabolism, it remains unclear whether this pathway directly drives the observed mood changes. Researchers did not measure brain serotonin levels, and urinary 5-HIAA is influenced by multiple bodily processes, including diet, gut motility, and kidney function.

How Many Walnuts Should You Eat?

In the study, participants consumed 40 grams of walnuts daily, equating to roughly 260 calories. Walnuts are dense in unsaturated fats and essential nutrients, making them a great addition to a balanced diet.

Nonetheless, this does not mean one must consume precisely 40 grams a day to reap their health benefits or that this exact amount is specifically required for mood enhancement. It is also important to consider the study's limitations: it featured only 31 participants, predominantly young and healthy women, and the participants were aware when they were eating walnuts, which could potentially introduce reporting bias.

Ultimately, walnuts remain a highly nutritious dietary addition, and this research offers an interesting clue that they may gently influence mood. However, it is far too early to claim they can treat depression, anxiety, or other mental disorders. Larger, longer-term studies are needed to determine if these effects are truly significant.