1. In this randomized controlled trial, a walnut-enriched diet was associated with a greater diversity of actively expressed genes in the gut microbiome than the other study diets.
2. A walnut-enriched diet also led to greater expression of metabolism-related genes and increased expression of the gene glycine amidinotransferase (GATM) in the gut microbiota.
Evidence Rating Level: 1 (Excellent)
Cardiovascular disease (CVD) affects a large population worldwide. Dietary patterns and consequent changes to the gut microbiome have been suggested to play a role in the development of CVD. Higher nut intake has been shown to be associated with decreased CVD risks, but the effect of specific nut intake on the gut microbiome is poorly understood. The present study aimed to evaluate the effect of walnut intake on the gut microbiome and determine potential implications for CVD reduction.
This randomized, cross-over study included 35 adult participants (aged 30-65) who were recruited between October 2014 and September 2017. Participants were included if they
had overweight or obesity and had elevated blood pressure and/or elevated low-density lipoprotein (LDL) cholesterol. Participants who smoked, had a systolic blood pressure ≥160, or a history of myocardial infarction, stroke, diabetes, liver, kidney, thyroid, gastrointestinal, and inflammatory diseases were excluded. Participants were provided a 2-week standard western diet and were then randomized to a random sequence of walnut-enriched diet (WD), a fatty-acid matched diet devoid of walnuts (WFMD), and a diet where oleic acid replaces alpha-linolenic acid (ORAD) for two weeks each. The primary outcome measured was the microbiome species and gene expression in the fecal samples after each test diet period.
The results demonstrated that the diversity of actively expressed genes was greater following WD than the WFMD and ORAD diets. Specifically, greater expression of metabolism-related genes and the gene glycine amidinotransferase (GATM) by gut microbiota Gordonibacter was observed following WD versus the WFMD and ORAD diets. Lastly, several species from the Actinobacteria and Firmicutes phyla were differentially more abundant following the WD, WFMD, and ORAD compared to the standard western diet. This study was limited by the exploratory nature of the observation, which limited the ability to make interpretations about causality. Nonetheless, these results suggested possible mechanisms underpinning the potential benefit of walnut consumption in CVD risk reduction and should be further explored.
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