The Gut Microbiome Modulates the Association Between Healthful Plant-Based Diet and Age-Related Cognitive Function Among Community-Dwelling Older Adults

Objectives: We aimed to determine the impact of walnut consumption on the gut microbiome, serum and fecal bile acid profiles, systemic inflammation, and oral glucose tolerance to a mixed-meal challenge.Methods: Adults (n30) with obesity (BMI > 37 + 6 kg/m2; 43.7 + 11.3 y) without diabetes or gastrointestinal diseases were enrolled in a randomized, controlled, crossover, complete feeding trial with three 3-wk conditions, each identical except for walnut halves (WH), walnut oil (WO), or corn oil (CO) in the diet.A 3-wk washout separated each condition.Fecal samples were collected on days 18-20.On day 20, participants underwent a 6h mixed-meal tolerance test (75g glucose + treatment) with a fasting blood draw followed by blood sampling every 30min.Fecal microbiome and microbiota were assessed using metagenomic and amplicon sequencing, respectively.Fecal microbial metabolites were quantified using GC/MS.Blood glucose, insulin, and inflammatory biomarkers (IL-6, TNF, CRP, and LBP) were quantified.Fecal and circulating bile acids were measured via LC-MS/MS.Gut permeability was assessed by quantifying 24h urinary excretion of orally ingested sucralose and erythritol on day 21.Statistical analysis used linear mixed-effects models and repeated measures ANOVA.Results: Roseburia spp.were greatest following WH (3.9 AE 0.6%) vs WO (1.6 AE 0.3%) and CO (1.9 AE 0.01%); Lachnospiraceae UCG-001 and UCG-004 were also greatest with WH vs WO