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Research Summary

BL21 probiotic improves glycemic control in type 2 diabetes patients

Moderate confidence
Low bias
Last updated June 18, 2026

Key Takeaway:

This study evaluated the efficacy and safety of Bifidobacterium longum subsp. longum BL21 as an adjunctive therapy to metformin in patients with type 2 diabetes, finding a significant reduction in HbA1c levels.

Study at a Glance

Participants

Intervention

Bifidobacterium longum subsp. longum BL21, Placebo

Outcomes

HbA1c, fasting blood glucose (FBG), insulin resistance (HOMA-IR), lipid profiles, gut microbiota composition, HbA1c levels (Placebo)

Funding

Non-Industry Sponsored

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Main Effects

Supplementation with BL21 led to a significant reduction in HbA1c levels (p = 0.026).

Non-significant trends toward reduction were observed for fasting blood glucose.

Gut microbiota analysis revealed an increase in beneficial genera, including Bifidobacterium and Faecalibacterium.

Evidence Summary

InterventionOutcomeMeasured ChangeStudy Effect
Supplements
Bifidobacterium longum subsp. longum BL21
(Supplements)
Glycemic Control
Fasting blood sugar (FBS)
(Glycemic Control)
No Change
Unclear
Supplements
Bifidobacterium longum subsp. longum BL21
(Supplements)
Metabolic Health
gut microbiota composition
(Metabolic Health)
Increase
Strong
Supplements
Bifidobacterium longum subsp. longum BL21
(Supplements)
Glycemic Control
HbA1c
(Glycemic Control)
Decrease
Strong
Supplements
Bifidobacterium longum subsp. longum BL21
(Supplements)
Metabolic Health
Insulin resistance
(Metabolic Health)
No Change
Unclear
Supplements
Bifidobacterium longum subsp. longum BL21
(Supplements)
Metabolic Health
lipid profiles
(Metabolic Health)
No Change
Unclear
Medications
Placebo
(Medications)
Glycemic Control
HbA1c levels (Placebo)
(Glycemic Control)
No Change
Unclear

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evidence suggest

Evidence Suggest

  • HbA1c levels decreased by 0.3% in the intervention group (p = 0.026).
  • No significant change in HbA1c levels was observed in the placebo group.
  • Trends toward improvement in fasting blood glucose and insulin resistance were noted.
who this applies

Who this applies to

  • Adults diagnosed with type 2 diabetes mellitus.
  • Patients currently receiving metformin therapy.
keep in mind

Keep in Mind

  • Results may not apply to populations outside the study's demographic.
  • The study did not measure long-term effects beyond the trial duration.
  • Further research is needed to confirm the findings and explore mechanisms.
between the lines

Between the Lines

  • The study's sample size may limit the generalizability of the findings.
  • Non-significant trends in other outcomes suggest further research is needed.
  • The study duration may not be sufficient to assess long-term effects.

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Journal Reference

Chengsheng Z, Yinhua L, Yanyan C, et al. Efficacy and Safety of Bifidobacterium longum subsp. longum BL21 as an Adjunctive Therapy to Metformin in Patients with Type 2 Diabetes Mellitus: A Randomized, Double-Blind, Placebo-Controlled Trial. Food Science & Nutrition. 2026;14(1):e71437. doi:10.1002/fsn3.71437

View DOIView on PubMedView on PMC

Connected Evidence

Discover how this study fits into the broader diabetes evidence landscape.

This study contributes to evidence on Probiotics and Synbiotics and gut microbiota composition, Probiotics and Synbiotics and Glycemic Control.

Related evidence relationships

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This study contributes to the evidence on the following intervention–outcome relationships.

Questions this evidence helps answer

Key clinical and research questions this study contributes to.

Does bifidobacterium longum subsp. longum bl21 improve gut microbiota composition?

Based on connected evidence for Bifidobacterium longum subsp. longum BL21 and gut microbiota composition.

Does bifidobacterium longum subsp. longum bl21 affect HbA1c in people with diabetes?

Exploring evidence on Bifidobacterium longum subsp. longum BL21 and HbA1c outcomes.

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