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Feeding Microbes: Nutrition, Microbiome, Metabolism, and Health (Oral Session 6)

(OR06-04-25) Microbial and Metabolic Impact of Walnut Consumption in Adults With Obesity

Sunday, June 1, 2025
10:36 AM – 10:48 AM ET
Location: S230 CD
Emerging Leaders in Nutrition Science Poster Competition
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 (n=30) 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, TNFα, 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 ± 0.6%) vs WO (1.6 ± 0.3%) and CO (1.9 ± 0.01%); Lachnospiraceae UCG-001 and UCG-004 were also greatest with WH vs WO and CO. WH fecal isobutyrate concentrations (5.41 ± 0.59 µmol/g) were lower than WO (7.17 ± 0.62 µmol/g) and CO (7.77 ± 0.72 µmol/g). Fecal isovalerate concentrations were lowest with WH (7.84±0.93 µmol/g) vs WO (10.3±0.99 µmol/g) and CO (11.6 ± 1.11 µmol/g). Indoles were highest in WH (36.8 ± 7.86 µmol/g) vs WO (6.78 ± 7.20 µmol/g) and CO (8.67 ± 9.54 µmol/g). There were no differences in glucose concentrations among groups. Insulin 2h AUC was lower with WH (469 ± 51.9 µIU/mL/min) and WO (494 ± 62.6 µIU/mL/min) vs CO (604 ± 57.5 µIU/mL/min) while glycolithocholic acid 4h AUC was lower with WH vs WO and CO. Sucralose recovery was lowest following WH (10.5 ± 1.2%) vs WO (14.3 ± 1.5%) and CO (14.6 ± 1.4%).

Conclusions: Walnut modified the fecal microbiota and metabolome, improved insulin response, and reduced gut permeability. Further bile acid and microbiome analyses are ongoing.

Funding Sources: USDA NIFA grant no. 2020-67017-30836/project accession no. 1021932