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Walnuts and Vegetable Oils Containing Oleic Acid Differentially Affect the Gut Microbiota and Associations with Cardiovascular Risk Factors: Follow-up of a Randomized, Controlled, Feeding Trial in Adults at Risk for Cardiovascular Disease.
Tindall, AM, McLimans, CJ, Petersen, KS, Kris-Etherton, PM, Lamendella, R
The Journal of nutrition. 2020;150(4):806-817
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Recent evidence suggests that microbes present in the gut may have a role in the risk of heart disease development. Walnuts have in previous studies shown to be of benefit for cardiovascular health and gut microbes are thought to be the mediator of this. This secondary analysis of a randomised control trial aimed to assess diets which differentiated in walnut composition on the species diversity of gut microbes and heart disease risk in 46 individuals with obesity over an 18-week period. The results showed that a diet of walnuts and the fats they contain enriched the microbes present in the gut compared to a Western-style diet. Interestingly, a whole walnut diet showed enrichment of a species that is better able to break down and use the components of walnuts compared to a diet where only the walnut fats were present. When on a diet rich in walnuts, an increase in a species of gut bacteria related to improved heart disease risk factors was observed. It was concluded that the positive effects of walnuts on gut bacteria and heart disease risk are due to the fibre and bioactive compounds, not simply the fats they contain. This study could be used by health care professionals to recommend the inclusion of whole walnuts into the diet of individuals with obesity to enrich gut bacteria that are involved in reducing heart disease risk.
Abstract
BACKGROUND It is unclear whether the favorable effects of walnuts on the gut microbiota are attributable to the fatty acids, including α-linolenic acid (ALA), and/or the bioactive compounds and fiber. OBJECTIVE This study examined between-diet gut bacterial differences in individuals at increased cardiovascular risk following diets that replace SFAs with walnuts or vegetable oils. METHODS Forty-two adults at cardiovascular risk were included in a randomized, crossover, controlled-feeding trial that provided a 2-wk standard Western diet (SWD) run-in and three 6-wk isocaloric study diets: a diet containing whole walnuts (WD; 57-99 g/d walnuts; 2.7% ALA), a fatty acid-matched diet devoid of walnuts (walnut fatty acid-matched diet; WFMD; 2.6% ALA), and a diet replacing ALA with oleic acid without walnuts (oleic acid replaces ALA diet; ORAD; 0.4% ALA). Fecal samples were collected following the run-in and study diets to assess gut microbiota with 16S rRNA sequencing and Qiime2 for amplicon sequence variant picking. RESULTS Subjects had elevated BMI (30 ± 1 kg/m2), blood pressure (121 ± 2/77 ± 1 mmHg), and LDL cholesterol (120 ± 5 mg/dL). Following the WD, Roseburia [relative abundance (RA) = 4.2%, linear discriminant analysis (LDA) = 4], Eubacterium eligensgroup (RA = 1.4%, LDA = 4), LachnospiraceaeUCG001 (RA = 1.2%, LDA = 3.2), Lachnospiraceae UCG004 (RA = 1.0%, LDA = 3), and Leuconostocaceae (RA = 0.03%, LDA = 2.8) were most abundant relative to taxa in the SWD (P ≤ 0.05 for all). The WD was also enriched in Gordonibacter relative to the WFMD. Roseburia (3.6%, LDA = 4) and Eubacterium eligensgroup (RA = 1.5%, LDA = 3.4) were abundant following the WFMD, and Clostridialesvadin BB60group (RA = 0.3%, LDA = 2) and gutmetagenome (RA = 0.2%, LDA = 2) were most abundant following the ORAD relative to the SWD (P ≤ 0.05 for all). Lachnospiraceae were inversely correlated with blood pressure and lipid/lipoprotein measurements following the WD. CONCLUSIONS The results indicate similar enrichment of Roseburia following the WD and WFMD, which could be explained by the fatty acid composition. Gordonibacter enrichment and the inverse association between Lachnospiraceae and cardiovascular risk factors following the WD suggest that the gut microbiota may contribute to the health benefits of walnut consumption in adults at cardiovascular risk. This trial was registered at clinicaltrials.gov as NCT02210767.
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A Walnut-Enriched Diet Affects Gut Microbiome in Healthy Caucasian Subjects: A Randomized, Controlled Trial.
Bamberger, C, Rossmeier, A, Lechner, K, Wu, L, Waldmann, E, Fischer, S, Stark, RG, Altenhofer, J, Henze, K, Parhofer, KG
Nutrients. 2018;10(2)
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There is a clear link between health, disease and the diversity of the human gut microbiome. Diet is one of the main factors that influences microbial composition in the gut. The aim of this study was to investigate the effect of walnut consumption on the gut microbiome composition and microbial diversity. 194 healthy adults, of average age 63 years, were included in this study. Participants were allocated to two diet phases of eight weeks each. 96 subjects first followed a walnut-enriched diet (43g walnuts/day) and then switched to a nut-free diet, while 98 subjects followed the diets in reverse order. While consuming the walnut-enriched diet, participants were advised to either reduce fat or carbohydrates or both to account for the additional calories. Faecal samples were collected at the end of the walnut-diet and the control-diet period for microbiome analyses. Walnut consumption significantly affected microbiome composition and diversity. The abundance of Ruminococcaceae and Bifidobacteria increased significantly while Clostridium species decreased significantly after walnut consumption. The effect of walnut consumption on the microbiome only marginally depended on whether subjects replaced fat, carbohydrates or both while on walnuts. The authors concluded that daily intake of 43 g walnuts over eight weeks significantly affects the gut microbiome by enhancing probiotic- and butyric acid-producing species in healthy individuals.
Abstract
Regular walnut consumption is associated with better health. We have previously shown that eight weeks of walnut consumption (43 g/day) significantly improves lipids in healthy subjects. In the same study, gut microbiome was evaluated. We included 194 healthy subjects (134 females, 63 ± 7 years, BMI 25.1 ± 4.0 kg/m²) in a randomized, controlled, prospective, cross-over study. Following a nut-free run-in period, subjects were randomized to two diet phases (eight weeks each); 96 subjects first followed a walnut-enriched diet (43 g/day) and then switched to a nut-free diet, while 98 subjects followed the diets in reverse order. While consuming the walnut-enriched diet, subjects were advised to either reduce fat or carbohydrates or both to account for the additional calories. Fecal samples were collected from 135 subjects at the end of the walnut-diet and the control-diet period for microbiome analyses. The 16S rRNA gene sequencing data was clustered with a 97% similarity into Operational Taxonomic Units (OTUs). UniFrac distances were used to determine diversity between groups. Differential abundance was evaluated using the Kruskal-Wallis rank sum test. All analyses were performed using Rhea. Generalized UniFrac distance shows that walnut consumption significantly affects microbiome composition and diversity. Multidimensional scaling (metric and non-metric) indicates dissimilarities of approximately 5% between walnut and control (p = 0.02). The abundance of Ruminococcaceae and Bifidobacteria increased significantly (p < 0.02) while Clostridium sp. cluster XIVa species (Blautia; Anaerostipes) decreased significantly (p < 0.05) during walnut consumption. The effect of walnut consumption on the microbiome only marginally depended on whether subjects replaced fat, carbohydrates or both while on walnuts. Daily intake of 43 g walnuts over eight weeks significantly affects the gut microbiome by enhancing probiotic- and butyric acid-producing species in healthy individuals. Further evaluation is required to establish whether these changes are preserved during longer walnut consumption and how these are linked to the observed changes in lipid metabolism.