Research Summary

Probiotics reduce GI side effects of metformin without improving metabolic efficacy

Moderate confidence

Low bias

Last updated June 19, 2026

Key Takeaway:

This study investigated whether multi-strain probiotic supplementation enhances the metabolic effects of metformin in women with elevated HOMA-IR, finding no significant improvements.

Study at a Glance

What was studied

Multi-strain probiotic added to metformin in adults with type 2 diabetes.

Participants

Young Adult (19–39), Middle Aged (40-64)

Male, Female

with T2 Diabetes

Intervention

Metformin + Multi-strain Probiotic

Outcomes

Gastrointestinal symptoms frequency, Abnormal stool frequency, Hard or lumpy stools, Fasting Plasma Glucose (FPG), Insulin resistance, RBP4, Total cholesterol

Funding

Non-Industry Sponsored

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Main Effects

Probiotic group reported 26% gastrointestinal symptoms vs. 52% in placebo (p < 0.05).

Probiotic group reported 18% abnormal stool frequency vs. 51% in placebo (p < 0.05).

No significant differences in fasting plasma glucose or insulin resistance between groups.

Evidence Summary

Intervention	Outcome	Measured Change	Study Effect
Multi-species synbiotic (12 probiotic strains + FOS prebiotic) (Supplements)	Abnormal stool frequency (Safety)	Decrease	Strong
Multi-species synbiotic (12 probiotic strains + FOS prebiotic) (Supplements)	Fasting Plasma Glucose (FPG) (Glycemic Control)	No Change	Unclear
Multi-species synbiotic (12 probiotic strains + FOS prebiotic) (Supplements)	Gastrointestinal symptoms frequency (Safety)	Decrease	Strong
Multi-species synbiotic (12 probiotic strains + FOS prebiotic) (Supplements)	Hard or lumpy stools (Safety)	Decrease	Strong
Multi-species synbiotic (12 probiotic strains + FOS prebiotic) (Supplements)	Insulin resistance (Metabolic Health)	No Change	Unclear
Multi-species synbiotic (12 probiotic strains + FOS prebiotic) (Supplements)	Retinol-Binding Protein 4 (RBP4) (Metabolic Health)	No Change	Unclear
Multi-species synbiotic (12 probiotic strains + FOS prebiotic) (Supplements)	Total cholesterol (Metabolic Health)	No Change	Unclear

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Evidence Suggest

Probiotic supplementation reduced gastrointestinal symptoms by 26%.
Abnormal stool frequency decreased by 33% in the probiotic group.
No significant changes in metabolic markers like fasting plasma glucose.

Who this applies to

Women diagnosed with insulin resistance or elevated HOMA-IR.
Patients currently prescribed metformin for diabetes management.

Keep in Mind

Results may not apply to men or other populations.
The study did not assess long-term effects of probiotic use.
Further research is needed to explore different probiotic strains or dosages.

Between the Lines

Limited to women with elevated HOMA-IR, affecting generalizability.
Small sample size may limit the robustness of findings.
Short duration of the study may not capture long-term effects.

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Journal Reference

Marzena R, Agnieszka B, Katarzyna M, et al. Multi-strain Probiotic Supplementation Does Not Enhance Metabolic Efficacy of Metformin in Women with Elevated HOMA-IR. Frontiers in Endocrinology. 2026;17:1765741. doi:10.3389/fendo.2026.1765741

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