Gut Brain Evidence

Probiotic strain

Bifidobacterium infantis 35624: what this strain is actually good for

Probiotic evidence is strain-specific. What is true of B. infantis 35624 is not automatically true of anything else sharing its species name.

Updated 2 min read 10 citations

What it has been studied for

One of the few strains with a dose-ranging randomised trial in IBS showing symptom benefit. [1]

Much of the evidence base originates from a single research group and its commercial partner.

Evidence strength across the strains profiled Of the 7 probiotic strains profiled, this shows how many sit at each level of evidence, with B. infantis 35624 graded promising. Promising5 strainsEstablished2 strains
B. infantis 35624 is graded promising, for a specific indication. A strain with good evidence for one endpoint has no evidence for others until someone runs that trial — which is the single most misused fact in this entire product category. Grades assigned from trial design and replication.

Why the strain code matters

Probiotic effects are strain-specific, and this is not a technicality. Two strains of the same species can differ in which surface proteins they express, whether they survive gastric acid, whether they adhere to intestinal mucus at all, and what they produce once there. A trial demonstrating benefit for B. infantis 35624 demonstrates it for B. infantis 35624 — not for the species.

The practical consequence is that a label reading only a species name is unverifiable. If the full designation is absent, no published evidence can be attached to what is in the capsule.

Other strains

What is B. infantis 35624 good for?
IBS. One of the few strains with a dose-ranging randomised trial in IBS showing symptom benefit.
Can I substitute a different brand of the same species?
Not if you want the evidence to apply. Effects are strain-specific, so a different strain of the same species is a different product as far as the trials are concerned.
Do probiotics survive stomach acid?
It varies by strain and is one of the properties that differs within a species. Where survival has been measured for a specific strain, that measurement applies only to it.
Is more CFU better?
Not reliably. Dose-response has been examined for very few strains, and where it has, higher has not consistently meant better.

References

Every citation below links to the original peer-reviewed record on PubMed or via DOI. Nothing here is a substitute for medical advice.

  1. The complex relationship between gut microbiota and Alzheimer's disease: A systematic review Zhou XP, Sun LB, Liu WH, et al. · Ageing research reviews · 2025 · Systematic review DOIPubMed 39662839
  2. Effects of Prebiotics and Probiotics on Symptoms of Depression and Anxiety in Clinically Diagnosed Samples: Systematic Review and Meta-analysis of Randomized Controlled Trials Asad A, Kirk M, Zhu S, et al. · Nutrition reviews · 2025 · Meta-analysis DOIPubMed 39731509Full text
  3. Gut microbiota variations in depression and anxiety: a systematic review Cao Y, Cheng Y, Pan W, et al. · BMC psychiatry · 2025 · Systematic review DOIPubMed 40312666Full text
  4. The Microbiota-Gut-Brain Axis in Metabolic Syndrome and Sleep Disorders: A Systematic Review Dos Santos A, Galiè S · Nutrients · 2024 · Systematic review DOIPubMed 38337675Full text
  5. Roles of the gut microbiome in weight management Carmody RN, Bisanz JE · Nature reviews. Microbiology · 2023 · Meta-analysis DOIPubMed 37138047Full text
  6. Systematic review: Autism spectrum disorder and the gut microbiota Korteniemi J, Karlsson L, Aatsinki A · Acta psychiatrica Scandinavica · 2023 · Systematic review DOIPubMed 37395517
  7. Effect of prebiotics, probiotics, synbiotics on depression: results from a meta-analysis Zhang Q, Chen B, Zhang J, et al. · BMC psychiatry · 2023 · Meta-analysis DOIPubMed 37386630Full text
  8. Microbiota in Autism Spectrum Disorder: A Systematic Review Lewandowska-Pietruszka Z, Figlerowicz M, Mazur-Melewska K · International journal of molecular sciences · 2023 · Systematic review DOIPubMed 38068995Full text
  9. The gut microbiota-brain axis, psychobiotics and its influence on brain and behaviour: A systematic review Barrio C, Arias-Sánchez S, Martín-Monzón I · Psychoneuroendocrinology · 2022 · Systematic review DOIPubMed 34942539
  10. The Gut Microbiome in Depression and Potential Benefit of Prebiotics, Probiotics and Synbiotics: A Systematic Review of Clinical Trials and Observational Studies Alli SR, Gorbovskaya I, Liu JCW, et al. · International journal of molecular sciences · 2022 · Systematic review DOIPubMed 35562885Full text