Eating 40 grams of walnuts daily for 8 weeks significantly improved mood in young adults, reducing total mood disturbance scores by 4.85 points according to a 2026 randomized controlled trial. The improvement was accompanied by increased levels of 5-HIAA, a serotonin metabolite linked to happiness, suggesting walnuts may boost the brain’s natural mood-regulating chemicals.
A new study found that eating a small handful of walnuts every day for 8 weeks improved mood in young adults. Researchers discovered that walnuts increased levels of a brain chemical linked to happiness and reduced overall mood disturbance. The study also found that walnuts created special compounds in the body that may help explain why they’re good for mental health. According to Gram Research analysis, this suggests that adding walnuts to your diet could be a simple, natural way to support better emotional well-being.
Key Statistics
A 2026 randomized controlled trial of 31 young adults found that eating 40 grams of walnuts daily for 8 weeks reduced total mood disturbance scores by 4.85 points compared to a nut-free control period.
Walnut consumption increased urinary 5-HIAA levels, a serotonin metabolite, and increases in this chemical were significantly associated with reductions in fatigue and mood disturbance in the 31-participant study.
Urinary urolithin levels, compounds produced when gut bacteria break down walnut compounds, strongly correlated with increases in serotonin metabolites (correlation coefficients of 0.537 and 0.634) in the 2026 trial.
The Quick Take
- What they studied: Whether eating walnuts daily would improve mood and emotional well-being in healthy young adults
- Who participated: 31 healthy young adults with an average age of 24 years, mostly women, who had no serious health conditions
- Key finding: People who ate 40 grams (about a small handful) of walnuts every day for 8 weeks had significantly better moods, with mood disturbance scores dropping by 4.85 points compared to when they weren’t eating walnuts
- What it means for you: Adding a daily handful of walnuts to your diet may help improve your mood and reduce emotional disturbance, though more research is needed to confirm this works for everyone
The Research Details
This was a randomized crossover trial, which means each participant tried both conditions: eating walnuts and not eating walnuts. The study lasted 18 weeks total. For 8 weeks, participants ate 40 grams of walnuts daily (about a small handful). Then they had a 2-week break where they didn’t eat any nuts. Finally, they spent 8 weeks without walnuts as a comparison period. This design is powerful because each person serves as their own comparison, making it easier to see if walnuts actually caused the mood changes.
Researchers measured mood using validated questionnaires, which are scientifically tested surveys that ask people about their emotional state. They also collected urine samples to measure specific chemicals that might explain how walnuts affect mood. These included 5-HIAA, a breakdown product of serotonin (the brain’s happiness chemical), and urolithins, which are compounds created when your body processes walnuts.
This research design is important because it controls for individual differences. Since each person was tested in both conditions, we can be more confident that walnuts caused the mood improvement rather than other factors. The study also looked for biological markers, which are measurable signs in the body that might explain why walnuts help mood. This gives us clues about the actual mechanism, not just whether walnuts work.
The study was relatively small with only 31 participants, which limits how much we can generalize the findings to everyone. The sample was mostly female and consisted of young, healthy adults, so results may differ for older people or those with health conditions. The study was open-label, meaning participants knew they were eating walnuts, which could influence their mood reports. However, the study used validated mood questionnaires and measured biological markers, which strengthens the findings. The researchers used appropriate statistical methods to analyze the data.
What the Results Show
The main finding was clear: eating walnuts significantly improved mood. Participants’ total mood disturbance scores decreased by 4.85 points when eating walnuts compared to the control period. This means they felt noticeably better emotionally.
The study also found that walnuts increased a chemical in urine called 5-HIAA, which is a breakdown product of serotonin. Serotonin is the brain chemical responsible for happiness and well-being. Importantly, walnuts did not change cortisol levels, which is a stress hormone. This suggests walnuts work through the happiness pathway, not by reducing stress hormones.
The increases in 5-HIAA were directly linked to the mood improvements. People whose 5-HIAA levels increased the most also experienced the biggest reductions in fatigue and mood disturbance. This connection suggests that walnuts may improve mood by boosting serotonin activity in the brain.
Walnuts also increased urolithins, which are compounds created when your gut bacteria break down walnut compounds. These urolithins were strongly correlated with the increases in 5-HIAA, suggesting that your gut bacteria may play a role in how walnuts improve mood. This finding hints at a connection between gut health and mental health, though more research is needed to understand this relationship fully.
Previous research has shown that walnuts contain compounds that support brain health, including omega-3 fatty acids and polyphenols. However, this is one of the first studies to directly measure how walnuts affect mood in humans and to explore the biological mechanisms. The findings align with growing evidence that diet influences mental health and that gut bacteria may play a role in mood regulation. This study adds important human evidence to support what scientists have suspected about walnuts and mental well-being.
The study had several limitations worth noting. First, it included only 31 participants, mostly young women, so the results may not apply to men, older adults, or people with mental health conditions. Second, participants knew they were eating walnuts, which could influence their mood reports through placebo effect. Third, the study lasted only 8 weeks, so we don’t know if the benefits continue long-term or if they fade over time. Finally, while the study found associations between walnuts and mood-related chemicals, it doesn’t prove that walnuts cause these changes in everyone.
The Bottom Line
Based on this research, eating about 40 grams (a small handful) of walnuts daily may help improve mood and reduce emotional disturbance in young, healthy adults. This finding has moderate confidence because the study was well-designed but relatively small. Walnuts are a nutritious food with many other health benefits, so adding them to your diet is unlikely to cause harm. However, this single study is not enough to recommend walnuts as a treatment for mood disorders or depression.
Young, healthy adults looking for natural ways to support their mood may benefit from this research. People interested in nutrition and mental health should find this relevant. However, people with nut allergies should avoid walnuts. Those with diagnosed mood disorders or depression should not rely on walnuts alone and should consult their healthcare provider. More research is needed before recommending walnuts specifically for people with mental health conditions.
The study showed mood improvements after 8 weeks of daily walnut consumption. You might expect to notice changes within a similar timeframe, though individual results may vary. The benefits appeared to be present during the walnut-eating period and may reverse when walnuts are stopped, suggesting ongoing consumption is needed.
Frequently Asked Questions
Do walnuts really improve mood and mental health?
A 2026 study of 31 young adults found that eating 40 grams of walnuts daily for 8 weeks significantly improved mood, reducing mood disturbance by 4.85 points. The improvement was linked to increased serotonin metabolites in urine, suggesting a biological mechanism. However, more research is needed to confirm this works for everyone.
How many walnuts should I eat daily for mood benefits?
The study used 40 grams of walnuts daily, which is roughly a small handful or about 14 walnut halves. This amount significantly improved mood in participants after 8 weeks. Eating this quantity as part of a balanced diet appears safe for most healthy adults.
How long does it take for walnuts to improve mood?
In the study, mood improvements appeared after 8 weeks of daily walnut consumption. Individual results may vary, and you may notice changes sooner or later depending on your body. Consistent daily consumption appears necessary to maintain the benefits.
Can walnuts replace medication for depression or anxiety?
No. While this study shows walnuts may support mood in healthy young adults, they should not replace professional treatment for depression, anxiety, or other mental health conditions. If you have a diagnosed mood disorder, consult your healthcare provider before making dietary changes.
Why do walnuts improve mood according to this research?
Walnuts appear to work through the serotonin system, the brain’s happiness pathway. The study found that walnuts increased 5-HIAA, a serotonin metabolite, and this increase correlated with mood improvements. Gut bacteria breaking down walnut compounds may also play a role, though the exact mechanism needs further study.
Want to Apply This Research?
- Track daily walnut consumption (yes/no) and rate your mood each evening on a scale of 1 to 10. After 4 to 8 weeks, review your mood ratings on days you ate walnuts versus days you didn’t to see if a pattern emerges.
- Set a daily reminder to eat a small handful of walnuts (about 40 grams) at the same time each day, such as with breakfast or as an afternoon snack. Log this in your app to build consistency and track whether your mood improves over time.
- Use the app to log your mood daily using a simple scale. Create a chart that shows your mood over weeks, with walnuts marked on the calendar. After 8 weeks, compare your average mood during walnut weeks versus non-walnut weeks to see if there’s a personal benefit.
This research shows an association between walnut consumption and improved mood in a small study of healthy young adults. These findings should not be interpreted as medical advice or as a treatment for depression, anxiety, or other mental health conditions. If you have a diagnosed mood disorder or are taking medications for mental health, consult your healthcare provider before making significant dietary changes. Walnuts may cause allergic reactions in some people. Individual results may vary, and more research is needed to confirm these findings in diverse populations and over longer time periods.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.