Mixed tree nuts, cognition and gut microbiota: a 4-week, placebo-controlled, randomized crossover trial in healthy non-elderly adults

Haskell-Ramsay, Crystal, Dodd, Fiona L., Smith, Darren, Cuthbertson, Lewis, Nelson, Andrew, Lodge, John K. and Jackson, Philippa A. (2023) Mixed tree nuts, cognition and gut microbiota: a 4-week, placebo-controlled, randomized crossover trial in healthy non-elderly adults. Journal of Nutrition, 152 (12). pp. 2778-2788. ISSN 0022-3166


Beneficial effects of nut supplementation on cognitive function have previously been demonstrated in young and older adults. Alterations to gut microbiota have also been shown following tree nut consumption. However, no data exists on the effects of nuts on cognition and intestinal microbial communities assessed within the same study.

The study aimed to examine the effects of daily consumption of tree nuts for four weeks on cognitive function (primary outcome), mood, metabolomics, and gut microbial species (secondary outcomes) in healthy, non-elderly adults.

This randomized, placebo-controlled, double-blind, counterbalanced crossover study assessed the effects of four weeks' supplementation with 30 g/d mixed tree nuts versus placebo on cognition and mood in 79 healthy 18-49 year old adults. Metabolic responses, gut bacterial community structure and the potential for these to impact cognition were explored using a multi-omic approach. Bacterial community analysis was conducted in QIIME2.

Mixed model analysis indicated that nut consumption led to significant improvements to accuracy (placebo M = 92.2% vs. NUTS M = 94.5%; p = 0.019) and speed of response (placebo M = 788 ms vs. NUTS M = 757 ms; p = 0.004) on a picture recognition task. No significant changes to bacterial community alpha or beta diversity were observed when comparing nut consumption to the placebo arm. However, an unclassified Lachnospiraceae amplicon sequence variant (ASV) was significantly enriched in participants when supplemented with nuts (p = 0.015). No correlations were observed between the changes to picture recognition and the changes to the unclassified Lachnospiraceae ASV. There were no significant changes to the urinary metabolome.

These findings indicate a positive effect of nut on cognition following only 4-weeks' consumption in a healthy non-elderly sample, as well as upregulation of a microbial taxa associated with gut health. The effects appear to be independent of one another, but further exploration is required in those experiencing cognitive decline and/or gut dysbiosis. The study was registered at clinicaltrials.gov (identifier: NCT03500601).

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