Gut microbiota interventions may improve glycemic control and reduce complications in type 2 diabetes

Methodology

This systematic review followed PRISMA 2020 guidelines with a priori protocol registration. A comprehensive literature search was conducted across PubMed, Embase, Web of Science, and Cochrane Central from inception to September 2024 using MeSH terms and keywords combining "type 2 diabetes," "insulin resistance," "gut microbiota," "microbiome," "complications," "diet," "probiotics," "prebiotics," and "cardiometabolic risk." Eligibility criteria included randomized controlled trials or controlled dietary interventions in adults with T2DM, obesity, metabolic syndrome, or insulin resistance examining microbiome-directed therapies (probiotics, prebiotics, synbiotics, dietary modifications, personalized nutrition, or pharmacological interventions) with outcomes including glycemic parameters, cardiometabolic markers, diabetes complications, and gut microbiota composition.

Two independent reviewers screened titles, abstracts, and full texts, with discrepancies resolved by discussion or third reviewer. Data extraction captured study characteristics, participant demographics, intervention details, duration, and outcomes. Risk of bias was assessed using Cochrane Risk of Bias 2.0 tool evaluating randomization, deviations from interventions, missing data, outcome measurement, and result selection. From 411 initial records, 10 studies met inclusion criteria after removing duplicates and excluding animal studies, pediatric populations, non-randomized designs, and studies lacking both microbiota and metabolic outcomes. Given heterogeneity in interventions and outcomes, narrative synthesis was performed rather than meta-analysis.

Interventions

The review synthesized diverse microbiome-targeted interventions. Probiotic supplementation trials included live or pasteurized Akkermansia muciniphila (10^10 CFU daily for 3 months), Bifidobacterium breve combined with berberine (versus each alone or placebo), and heat-inactivated Bifidobacterium animalis subsp. lactis CECT8145 (10^10 CFU) combined with omega-3 (370 mg/day) and inulin (1.7 g/day) delivered in functional seafood sticks for 12 weeks.

Dietary interventions included Mediterranean diet (35% fat, 22% MUFA) versus low-fat high-complex carbohydrate diet (28% fat) for one year, sardine-enriched diet (100g sardines 5 days/week) versus standard diabetic diet for six months, and whole-grain rye with or without lignan supplementation versus whole-grain wheat for 8 weeks. White common bean extract providing α-amylase inhibition was administered at 1.5g before meals with normal carbohydrate intake for four months.

Pharmacological modulation compared empagliflozin (10 mg/day) versus metformin (1700 mg/day) for three months in treatment-naïve T2DM patients. Personalized nutrition interventions used machine learning algorithms integrating microbiome profiling with clinical features to generate individualized postprandial-targeting diets, or whole genome shotgun sequencing (BugSpeaks® platform) to guide tailored dietary recommendations, both for 3-6 months.

Key Findings

Gut microbiota-targeted interventions consistently improved glycemic control across multiple modalities. Pasteurized Akkermansia muciniphila produced a 28.6% improvement in insulin sensitivity and 34% reduction in insulinemia with modest reductions in body weight and cholesterol. Combined berberine plus Bifidobacterium breve significantly reduced postprandial cholesterol and LDL-C beyond either intervention alone through synergistic effects on gut microbiota and fatty acid metabolism. Personalized nutrition guided by microbiome profiling achieved superior glycemic outcomes compared to Mediterranean diet, with 61% of newly diagnosed T2DM patients achieving diabetes remission, HbA1c reductions of 0.39%, fasting glucose decreases of 16.4 mg/dL, and triglyceride reductions of 49 mg/dL over six months.

Cardiometabolic benefits extended beyond glycemic control. Empagliflozin uniquely improved cardiovascular risk markers through microbiota reshaping, enriching beneficial butyrate-producers (Roseburia, Faecalibacterium, Eubacterium) while reducing pathogenic species (Escherichia-Shigella, Bilophila). Functional seafood sticks reduced insulin by 5.25 mg/dL, HOMA-IR by 1.33, and pulse pressure by 4.69 mmHg in women, with microbiota changes correlating to metabolic improvements. White bean extract notably reduced diabetic peripheral neuropathy incidence and improved nerve conduction velocity alongside HbA1c reduction of 0.72%, mediated by enrichment of SCFA-producing bacteria. Across interventions, beneficial microbiota shifts consistently involved increased diversity, higher abundance of Bifidobacterium, Faecalibacterium, and Roseburia, and reduced pro-inflammatory taxa.

Comparison with other Studies

These findings align with and extend previous meta-analyses showing that probiotic supplementation modestly improves glycemic control in T2DM, with effect sizes for HbA1c reduction typically 0.4-0.6%. A 2016 meta-analysis by Sun et al. of 12 RCTs found probiotics reduced HbA1c by 0.54%, similar to the range observed in trials within this review. The superior efficacy of Akkermansia muciniphila compared to generic probiotics is consistent with emerging evidence that specific strains have distinct metabolic effects, with Akkermansia uniquely improving gut barrier function through mucin-binding proteins.

The cardiovascular benefits of empagliflozin mediated by microbiota changes complement findings from the EMPA-REG OUTCOME trial showing SGLT2 inhibitors reduce cardiovascular events independent of glucose lowering. This review provides mechanistic insight by demonstrating that empagliflozin enriches butyrate-producing bacteria and modifies bile acid and metabolite profiles, suggesting microbiome modulation as a novel pathway for cardioprotection. The efficacy of personalized nutrition guided by microbiome profiling achieving 61% diabetes remission is particularly notable and exceeds standard dietary interventions, corroborating recent precision medicine studies showing baseline microbiota composition can predict therapeutic response to dietary changes.

The finding that white bean extract reduced diabetic neuropathy is novel and extends limited prior evidence on dietary interventions affecting microvascular complications. Most diabetes nutrition trials focus on glycemic control with few assessing complication endpoints. The Mediterranean diet benefits on microbiota composition align with extensive literature showing this pattern enriches beneficial taxa, though the comparative efficacy versus low-fat diets for microbiome modulation remains debated. The heterogeneity in intervention effects across populations suggests host-microbiome interactions are complex and likely require personalized approaches rather than one-size-fits-all strategies.

Journal Reference

Ur Rehman M, Saeed H, Omer O, Tashfeen S. Gut Microbiota-Directed Interventions in Type 2 Diabetes: A Systematic Review of Clinical Outcomes and Complication Risk. Cureus. 2025;17(10):e95045. doi:10.7759/cureus.95045