The effects of nut intake on gut microbiome composition and gut function in adults: a systematic review and meta-analysis
Gut microbiome
Year Published: 2025
Journal
Adv Nutr
Authors
Matthew Snelson, Jessica R Biesiekierski, Susanna Chen, Nessmah Sultan, Barbara R Cardoso
Methods
The reduced risk of chronic diseases such as cardiovascular disease and type 2 diabetes associated with nut consumption may occur via modulation of the gut microbiota, although this has not been comprehensively assessed. This systematic review of clinical trials aims to assess the effects of nuts on gut microbiota composition and metabolites in adults. Further, it examines the effects of nuts on gut function and symptoms in adults. The systematic review was conducted following PRISMA guidelines and registered in PROSPERO (CRD42023451282). Outcomes included microbiota diversity, specific bacterial abundances, gastrointestinal symptoms, intestinal permeability, faecal pH, faecal moisture, and short-chain fatty acid (SCFAs) concentrations. We performed meta-analyses to assess the overall effect of nuts on faecal moisture, pH, intestinal permeability and SCFA concentrations. Amongst the 28 intervention trials included in this review, almonds were the most commonly studied (12 trials), while other nuts, such as walnuts, peanuts, pistachios and Brazil nuts, were also examined.
Key Findings
Key Findings: Nineteen articles reported the effects of almond, walnut, peanut or mixed nuts on the microbiota composition. Additionally, 6 trials used interventions involving a mixture of different nuts. A total of 19 trials assessed the community structure of the gut microbiota through the assessment of α-and β-diversity metrics, with most finding no significant differences following nut intervention. Regarding taxonomic changes, the majority of studies reported no significant changes across nut interventions. However, several studies noted increases in Clostridium and Roseburia, with mixed results for Bifidobacterium abundance following almond or walnut intervention. Five studies assessed faecal SCFA concentrations, with positive effects of nut interventions on propionate. There were no effects of nut interventions on faecal pH and intestinal permeability, with an unfavourable effect on faecal moisture. In summary, the available evidence indicates that nuts have modest effects on gut health, but the substantial heterogeneity between studies may hinder further conclusions.