Walnuts Improve Insulin Response and Gut Health in Obesity
A USDA-backed study links whole walnuts to better insulin sensitivity, reduced gut permeability, and favorable microbiome changes in adults with obesity
Topline
In a tightly controlled dietary study, whole walnuts but not walnut oil or corn oil improved insulin response and reduced gut permeability in adults with obesity, likely by enriching beneficial gut bacteria and modifying bile acid and metabolite profiles.
Study Details
Researchers from the University of Illinois Urbana-Champaign presented findings at the NUTRITION 2025 conference showing that walnut consumption can significantly impact metabolic and gut health in individuals with obesity. This builds upon earlier studies demonstrating walnut-induced microbiome enrichment in healthy individuals.
Methodology
This randomized, crossover feeding trial involved 30 adults with obesity (but no diabetes or GI disease). Each participant underwent three 3-week diet periods with controlled meals, incorporating either:
Whole walnut halves (WH)
Walnut oil (WO)
Corn oil (CO)
Each period was separated by a 3-week washout.
Assessments included:
Fecal microbiota (via sequencing)
Metabolites and bile acids (via chromatography)
Inflammatory and glycemic biomarkers
Gut permeability (via urinary recovery of sucralose/erythritol after ingestion)
Key Findings
Gut Bacteria: WH led to the highest levels of Roseburia, Lachnospiraceae UCG-001/004 linked to short-chain fatty acid production.
Insulin Sensitivity: 2-hour insulin AUC was lowest in the walnut halves group (469 µIU/mL/min), suggesting better insulin response.
Gut Barrier: WH resulted in the lowest sucralose recovery (10.5%), indicating reduced intestinal permeability.
Bile Acids: Lower glycolithocholic acid levels were seen with WH.
Metabolites: WH was associated with lower branched-chain fatty acids (isobutyrate, isovalerate) and higher levels of indoles compounds tied to mucosal protection.
Implications for Practice
For patients with obesity, incorporating whole walnuts not just walnut oil into the diet may:
Improve insulin response even without glucose changes
Reduce gut leakiness, a factor implicated in metabolic endotoxemia
Enhance beneficial microbial and metabolic profiles
For clinicians, these findings support recommending whole-food sources of fiber and polyphenols like walnuts rather than isolated oils.