Bifidobacterium longum BL21 probiotic may improve HbA1c when added to metformin in type 2 diabetes
Key takeaway:
A 12-week double-blind RCT in adults with T2DM found that adding Bifidobacterium longum BL21 to metformin significantly lowered HbA1c by 0.3% and favorably shifted gut microbiota compared to placebo.
Study at a glance
Study type
RCTs
duration
Short-Term (≤3 mo)
Intervention
Probiotics
Outcomes
HbA1c, Fasting Plasma Glucose, Insulin resistance, Triglycerides, Gut microbiota diversity
Funding
Non-industry sponsored
What was studied
Whether adding BL21 probiotic to metformin improves glycemic control in T2DM
What they found
- ↓ HbA1c (0.3% reduction vs placebo, p=0.026, meeting ADA MCID threshold)
- ↑ Beneficial gut bacteria (Bifidobacterium, Faecalibacterium enriched)
- → Fasting glucose, insulin resistance, triglycerides showed non-significant improvement trends
mainEffects
↓ HbA1c (0.3% reduction vs placebo, p=0.026, meeting ADA MCID threshold)
↑ Beneficial gut bacteria (Bifidobacterium, Faecalibacterium enriched)
→ Fasting glucose, insulin resistance, triglycerides showed non-significant improvement trends
Evidence Suggest
- BL21 significantly reduced HbA1c compared to placebo as an adjunct to metformin (p=0.026)
- Favorable gut microbiota changes with increased SCFA-producing genera and reduced pathogenic taxa
- Safety profile comparable to placebo with no serious adverse events reported
Who this applies to
Adults with type 2 diabetes currently taking metformin who have room for improvement in their blood sugar control and are interested in evidence-based probiotic options as a supportive therapy.
Keep in Mind
The HbA1c reduction of 0.3% is modest compared to prescription diabetes medications. The non-significant findings for fasting glucose and insulin resistance suggest not all metabolic parameters benefited. The study was also relatively small and short, so larger and longer trials are needed to confirm whether this effect lasts and who benefits most.
Between the Lines
- Small sample size without formal a priori power calculation
- 12-week duration may not capture long-term efficacy or sustainability
- Gut microbiota analysis was taxonomic/descriptive without direct SCFA measurement
Unlock Full Analysis
Create a free account to unlock the bias score, detailed effectiveness analysis, and clinical outcomes for this study.
Sources
American Diabetes Association Standards of Care in Diabetes—2025: Pharmacologic Approaches to Glycemic Treatment
Insulin Resistance & Type 1 | ADA
Standards of Care in Diabetes—2024
Type 2 diabetes in adults: management
A Guide for People with Type 2 Diabetes | American Diabetes Association
Diabetes Diagnosis & Tests | ADA
International Diabetes Federation - IDF Diabetes Atlas 10th Edition
NIH National Center for Complementary and Integrative Health - Probiotics: What You Need To Know
Comparative Efficacy and Safety of Ecnoglutide in Type 2 Diabetes: A Systematic Review and Meta-Analysis.
Beyond insulin therapy: Comparing relative benefits of adding SGLT2 versus DPP4 inhibitors in poorly controlled type 2 diabetic patients: A systematic review and meta-analysis.
The role of peripheral blood HIF-1α in pancreatic β-cell dysfunction and insulin resistance among patients with type 2 diabetes: a systematic review and meta-analysis.
Association between triglyceride-glucose (TyG) index and diabetic foot ulcers in adult inpatients with type 2 diabetes at hospital admission.
No ads. No tracking
A clean, privacy-first research experience.
Secure & private
Your data is always protected.
Always up to date
New studies added every day.