A 2 year randomised controlled trial, the WAHA study, examined the effect of daily walnut consumption on cognitive function and brain ageing biomarkers in 708 older adults. Walnut consumption significantly reduced LDL cholesterol, reduced inflammatory markers, and in a subgroup with higher cardiovascular risk, significantly slowed the decline in global cognition scores. The walnut group also showed significantly lower eicosanoid inflammation markers and better memory performance at the two-year follow-up.
Alpha-Linolenic Acid and the Brain
Walnuts are the tree nut with the highest ALA content at approximately 2.5 grams per 30-gram serving. ALA is a plant-based omega-3 that can be partially converted to EPA and DHA in the body, though conversion efficiency is low. ALA itself reduces inflammatory eicosanoid production by competing with arachidonic acid. Regular walnut consumption has been shown to reduce the omega-6 to omega-3 ratio in cell membranes, improving the anti-inflammatory character of tissue throughout the body.
Polyphenols and Microbiome Effects
Walnuts contain ellagitannins that are converted by gut bacteria to urolithins, compounds with anti-inflammatory and anti-cancer properties that accumulate in tissues including brain tissue. A clinical trial found that walnut consumption significantly increased the relative abundance of Faecalibacterium prausnitzii and Roseburia intestinalis, both anti-inflammatory butyrate producers, while reducing pathogenic Clostridium species.