A handful of walnuts a day may boost emotional well-being, study finds

Eating a handful of walnuts each day may benefit mental health, according to new research.

A study by researchers at the University of Barcelona, published in the international journal Food & Function, found that healthy young adults who consumed a daily handful of walnuts showed improvements in overall emotional well-being. The research was a randomized controlled clinical trial supported by the California Walnut Commission.

The study followed 31 healthy young adults living in Spain over 18 weeks. Participants ate 40 grams of walnuts daily for eight weeks. Overall negative emotional states were significantly lower during the walnut-consumption period compared with the control period. Levels of anger and fatigue also declined.

Changes in several metabolic markers were also observed. During the walnut-consumption period, urine samples showed significant increases in both urolithin — a metabolite of walnut polyphenols — and 5-HIAA, a key metabolite of serotonin.

Professor Izquierdo-Pulido, who led the study, said the findings were notable not only for the emotional improvements observed but also for the accompanying changes in biomarkers. "The association observed between urolithin and serotonin metabolism points to a new direction for studying the relationship between walnut consumption, gut microbiota and emotional well-being," she added.

A standard one-ounce (about 28-gram) serving of walnuts contains 4 grams of protein, 2 grams of dietary fiber, 38 milligrams of tryptophan and 42.6 milligrams of magnesium. Walnuts are also a source of alpha-linolenic acid, a plant-based omega-3 fatty acid.