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

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.

Nuts and their Effect on Gut Microbiota, Gut Function and Symptoms in Adults: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

“…Eight RCTs measured outcomes related to faecal microbiota including relative abundance at the phyla and genus levels, and metrics for alpha and beta diversity [ 16 , 17 , 18 , 19 , 20 , 21 , 27 ]. Three RCTs reported stool frequency [ 18 , 20 , 22 ] and two RCTs reported gut symptoms [ 18 , 22 ].…”

“…There were differences in analysis and reporting methods between the eight RCTs included in the meta-analyses. Methods of DNA extraction varied, with three studies using the MoBio power soil DNA isolation kit [ 17 , 19 , 21 ], one study using the QIAmp East DNA Stool Kit [ 18 ], one study using the Qiagen Powersoil DNA isolation kit [ 27 ], and three studies following previously published protocols with modifications [ 16 , 20 ]. Primers used to target the 16S gene also varied with three studies targeting the V4 region [ 17 , 19 , 27 ], three studies targeting V1–V3 regions [ 18 , 20 ], one study targeting the V3/4 regions [ 16 ], and one targeting the V4/5 regions [ 21 ].…”

“…Methods of DNA extraction varied, with three studies using the MoBio power soil DNA isolation kit [ 17 , 19 , 21 ], one study using the QIAmp East DNA Stool Kit [ 18 ], one study using the Qiagen Powersoil DNA isolation kit [ 27 ], and three studies following previously published protocols with modifications [ 16 , 20 ]. Primers used to target the 16S gene also varied with three studies targeting the V4 region [ 17 , 19 , 27 ], three studies targeting V1–V3 regions [ 18 , 20 ], one study targeting the V3/4 regions [ 16 ], and one targeting the V4/5 regions [ 21 ]. The reads following sequencing were reported as ‘reads per sample’ in one study (88,880 [ 17 ]), ‘reads per sample following quality filtering’ in two studies (28,680 and 33,194 respectively; [ 18 , 19 ]), and ‘total reads following quality filtering’ in four studies (range 3259–3008,191 [ 20 , 21 , 27 ]).…”

How strong is the evidence that gut microbiota composition can be influenced by lifestyle interventions in a cardio-protective way?

“…The role of nuts on gut microbiota has been studied elsewhere; in a cross-over study involving 18 healthy women, daily consumption of 42 g of walnuts was shown to modify the gut microbiota composition and to lower LDL cholesterol levels [55]. In another cross-over study involving 45 men and women at risk for CVD, walnuts (57-99 g/d), compared to a diet with the same amount of fatty acids but from different sources, other than walnuts, differentially influenced gut microbiota [56,57]. Thus, it may be that the benefits of nut consumption are partially mediated through the gut microbiota.…”

Gut microbiota metabolites as integral mediators in cardiovascular diseases (Review)

“…Epidemiological investigations have demonstrated that Western diets are high in sugar and fat and lack sufficient dietary fiber, all of which are associated with an increased risk of obesity and cVds (108). In addition, recent research from Tindall et al indicated that consuming FAs, bioactive compounds and the fiber in walnuts improved cardiovascular risk factors by regulating the abundance of intestinal flora (109). Moreover, it was reported that diindolylmethane and indole-3-methanol from cruciferous plants can reduce plasma TMAO levels by inhibiting flavin-containing monooxygenase, thereby preventing the development of cVds.…”