Eating a handful of walnuts every day may do more than just provide the body with healthy fats and nutrients. A new study published in the journal Food & Function suggests that regular walnut consumption may help improve mood and change serotonin-related metabolism. Researchers found that young adults who ate walnuts daily for eight weeks experienced a reduction in overall mood disturbance. Also, certain substances linked to serotonin metabolism increased in their urine.

Walnuts are already known for their nutritional benefits, including their omega-3 fatty acids, fibre and plant compounds. The new study adds to the growing interest in the relationship between diet, gut health and the brain. However, the findings do not mean that walnuts can treat depression or that they directly increase serotonin activity in the brain. Instead, the study highlights a possible link between eating walnuts, changes in the body's metabolism and improvements in mood.

What Did The Study Find?

The study looked at the effects of eating walnuts daily on mood and certain biological markers in young adults. Researchers conducted an 18-week randomised crossover trial involving 31 healthy adults who completed both parts of the study. Participants ate 40 grams of walnuts daily for eight weeks during one phase. During the other phase, they avoided walnuts and other nuts. A two-week break separated the two phases. The researchers assessed the participants' mood and collected urine samples to measure substances associated with serotonin metabolism, cortisol and compounds produced when gut bacteria process certain plant chemicals. The results showed that:

  • Overall mood disturbance decreased: Participants had lower total mood disturbance scores during the walnut-eating phase than during the period without nuts.
  • Serotonin-related metabolism changed: Urinary levels of 5-hydroxyindoleacetic acid, or 5-HIAA, increased significantly during walnut consumption.
  • Gut-derived compounds increased: Levels of urolithin A and urolithin B, which are produced when gut bacteria process certain compounds found in walnuts, also increased.
  • Not every measure improved: Researchers did not find significant differences in cortisol levels, perceived stress or overall well-being between the two conditions.

How Can Walnuts Affect Mood?

Walnuts have several nutrients and plant compounds that may help explain the potential link with emotional well-being.

  • Omega-3 fatty acids: Walnuts contain alpha-linolenic acid (ALA), a plant-based omega-3 fatty acid. Omega-3 fats support normal cell function and are important for the brain. However, more research is needed to establish how walnut-derived ALA affects mood.
  • Tryptophan: This essential amino acid is used by the body to make serotonin. Serotonin is a chemical messenger involved in regulating mood, sleep and appetite.
  • Fibre: Walnuts provide dietary fibre, which supports digestion and helps gut microbes produce useful substances.
  • Polyphenols: These plant compounds have antioxidant properties. Some, including ellagitannins, are broken down by gut bacteria into urolithins, which researchers are studying for their possible role in health.

Together, these components may influence several biological processes linked to the gut and brain.

What Is The Link Between Walnuts And Serotonin?

Serotonin is a neurotransmitter, which is a chemical messenger that helps nerve cells communicate. It plays a role in mood regulation, sleep, appetite and other bodily functions. The body produces serotonin using tryptophan obtained from food.

In the latest study, researchers measured 5-HIAA, a major breakdown product of serotonin, in urine. Higher urinary 5-HIAA levels were associated with lower overall mood disturbance. The researchers also found that increases in urolithin A and B were associated with increases in urinary 5-HIAA. The findings suggest that compounds produced when gut bacteria process walnuts may be linked to serotonin-related metabolism.

However, an important distinction is still present; urinary 5-HIAA reflects serotonin metabolism throughout the body. It does not directly measure serotonin levels or activity in the brain. Therefore, the study cannot establish that eating walnuts boosts brain serotonin.

How Many Walnuts Should You Eat Daily?

For the study, the researchers used 40 grams of walnuts a day, approximately a generous handful. You can add walnuts to your regular diet in several simple ways:

  • Add chopped walnuts to porridge, oats or breakfast cereal.
  • Mix them into plain yoghurt with fresh fruit.
  • Sprinkle them over salads for extra crunch.
  • Blend a few into smoothies.
  • Eat them as a snack instead of highly processed foods.

Walnuts are calorie-dense, so check your overall dietary needs and portion sizes.

Disclaimer: This content including advice provides generic information only. It is in no way a substitute for a qualified medical opinion. Always consult a specialist or your own doctor for more information. NDTV does not claim responsibility for this information.