What This Strain Does
Bifidobacterium longum subsp. infantis, commonly known as Bifidobacterium infantis or B. infantis, represents one of the most evolutionarily specialized probiotics known to science. As its name suggests, this subspecies is exquisitely adapted to thrive in the infant gut, where it typically dominates the microbiome of healthy breastfed babies. However, decades of clinical research have revealed that B. infantis also provides profound benefits for adults, particularly those suffering from irritable bowel syndrome and inflammatory gut conditions.
The specialized nature of B. infantis becomes apparent when examining its unique relationship with human milk oligosaccharides (HMOs), the complex sugars abundant in breast milk that cannot be digested by infants themselves. Unlike most gut bacteria, B. infantis possesses a complete genetic toolkit for consuming virtually all types of HMOs, allowing it to rapidly dominate the infant gut and exclude potentially harmful bacteria. This evolutionary specialization explains why B. infantis has become so closely associated with early human development.
What makes B. infantis particularly valuable for adult health is its exceptional anti-inflammatory capabilities. The bacterium modulates immune responses through multiple mechanisms, reducing the production of pro-inflammatory cytokines while increasing anti-inflammatory mediators. This immunomodulatory activity underlies its remarkable effectiveness for conditions where inflammation drives symptoms, particularly IBS.
B. infantis also strengthens intestinal barrier function by promoting tight junction protein expression and mucus production. These effects help seal the gut barrier against inappropriate permeability that can trigger systemic inflammation and immune activation. For individuals with compromised gut barriers, whether from IBS, inflammatory conditions, or other causes, B. infantis provides targeted support for restoration.
The strain produces short-chain fatty acids through fermentation of prebiotic fibers, with a particularly favorable profile that supports gut cell health and maintains an acidic environment inhospitable to pathogens. These metabolic contributions, combined with direct interactions with the immune system, make B. infantis a powerful therapeutic probiotic.
Research Highlights
B. infantis has accumulated an impressive body of clinical evidence, with particularly strong data for IBS treatment that has established it as one of the most evidence-based probiotic interventions available.
Landmark IBS Research: The most influential research on B. infantis comes from a series of rigorous clinical trials conducted by researchers in Cork, Ireland. A pivotal study published in the American Journal of Gastroenterology randomized over 360 women with IBS to receive B. infantis 35624 or placebo for four weeks. The probiotic group showed significant improvements in all cardinal IBS symptoms: abdominal pain, bloating, bowel dysfunction, incomplete evacuation, straining, and passage of gas. Remarkably, the proportion of patients reporting adequate relief was nearly twice as high in the B. infantis group compared to placebo.
Dose-Ranging Studies: Research has helped establish optimal dosing for B. infantis. Studies found that doses of approximately 1 billion CFU daily were as effective as higher doses for IBS symptom relief, while very low doses showed diminished benefits. This finding has practical implications for product selection and cost-effectiveness.
Immune and Inflammatory Markers: Clinical research has documented B. infantis’s effects on measurable inflammatory markers. Studies have shown that supplementation normalizes the ratio of pro-inflammatory to anti-inflammatory cytokines in the bloodstream, reducing markers like IL-6, TNF-alpha, and C-reactive protein. These changes correlate with symptom improvement and provide objective evidence of the strain’s anti-inflammatory mechanism.
Infant Microbiome Restoration: Research has revealed a concerning decline in B. infantis colonization in Western infants compared to historical norms and to infants in developing countries with more traditional practices. Clinical trials have demonstrated that supplementing breastfed infants with B. infantis restores dominance of this beneficial organism, reduces markers of gut inflammation, and decreases abundance of potentially harmful bacteria. The implications for long-term health are being actively investigated.
Inflammatory Bowel Disease: While less extensive than IBS research, studies in inflammatory bowel disease populations have shown promising effects. B. infantis supplementation reduced inflammatory markers and improved symptoms in patients with ulcerative colitis, though more research is needed to establish its role in IBD management.
Specific Strains to Look For
The most extensively researched B. infantis strain by far is:
B. infantis 35624 (Alimentary Health/Align): This strain has become synonymous with B. infantis research, with the majority of clinical evidence for IBS treatment derived from studies using this specific isolate. Originally developed by researchers at University College Cork, B. infantis 35624 forms the active ingredient in the Align probiotic brand. Its documented effects on IBS symptoms across multiple rigorous trials make it the gold standard for probiotic IBS treatment.
B. infantis EVC001 (Evivo): This strain has been specifically developed for infant supplementation and has accumulated substantial research demonstrating its ability to restore B. infantis dominance in the infant gut microbiome. Studies have shown that EVC001 supplementation dramatically increases B. infantis populations, reduces populations of potentially harmful bacteria, and decreases gut inflammation markers in infants.
B. infantis M-63 (Morinaga): This strain has been studied for various applications including allergies and gut health, with research supporting its immunomodulatory properties.
When selecting B. infantis products for IBS, specifically seeking out products containing the 35624 strain provides the greatest confidence that you will receive the documented benefits, as strain-specific effects cannot be assumed to apply to all B. infantis isolates.
What to Look For in Products
Choosing an effective B. infantis product requires careful attention to several factors:
Strain Verification: For IBS treatment, the 35624 strain has by far the strongest evidence base. While other B. infantis strains may provide benefits, assuming equivalence to 35624 is not scientifically justified. Products that specify strain designation provide greater assurance of receiving research-backed benefits.
Dosage: Clinical research has established that approximately 1 billion CFU daily is effective for IBS symptom relief. Higher doses have not shown superior benefits in clinical trials, making B. infantis one of the rare probiotics where “more is not necessarily better” has been demonstrated. This finding simplifies product selection and can reduce costs.
Monotherapy vs. Combinations: Interestingly, some research suggests that B. infantis may perform better as a single-strain product rather than in complex multi-strain combinations. One study found that B. infantis 35624 alone outperformed a combination product containing the same strain alongside other probiotics. While the reasons are not fully understood, this finding suggests that stand-alone B. infantis products may be preferred for IBS specifically.
Delivery and Stability: B. infantis can be sensitive to environmental conditions. Products with stability guarantees through end of shelf life provide better assurance than those stating CFU counts only at manufacture. Refrigerated products may maintain higher viable counts, though well-formulated shelf-stable products can also be effective.
Product Source: For IBS treatment, Align is the most direct source of B. infantis 35624, as it was developed specifically around this research-backed strain. Other products containing B. infantis may use different strains with less clinical validation.
Potential Side Effects
Bifidobacterium infantis is considered extremely safe, consistent with its role as the dominant gut bacterium in healthy breastfed infants. Adverse effects are uncommon and typically minor.
Some individuals may experience mild digestive symptoms when first beginning supplementation, including temporary changes in gas, bloating, or bowel habits as the gut microbiome adjusts to the new population. These effects generally resolve within one to two weeks of continued use. Starting with the recommended dose rather than higher amounts can help minimize initial adjustment effects.
For infants, B. infantis has demonstrated excellent safety even in premature populations. However, parents should consult pediatricians before giving probiotics to infants, particularly those with health conditions or who were born prematurely.
Those with severely compromised immune systems or central venous catheters should consult healthcare providers before using any probiotic products. While B. infantis is considered safe for most immunocompromised individuals, medical guidance is appropriate for those at highest risk.
Pregnant and breastfeeding women can typically use B. infantis safely, as it is a natural component of the healthy gut microbiome. Indeed, maternal B. infantis populations may influence transmission to infants during and after birth.
How to Take
For optimal results with B. infantis supplementation, following evidence-based guidance improves outcomes:
Consistency: Clinical trials demonstrating IBS benefits involved consistent daily use over at least four weeks. While some individuals notice improvements sooner, allowing adequate time for the full effect to develop is important. Continuous supplementation appears necessary to maintain benefits, as effects may wane if supplementation is discontinued.
Timing: B. infantis can be taken at any time of day, though some evidence suggests taking probiotics with or shortly before meals may improve survival through stomach acid. Maintaining a consistent time helps ensure you remember to take it daily.
IBS-Specific Guidance: For IBS treatment, the single-strain approach with B. infantis 35624 at approximately 1 billion CFU daily represents the most evidence-based protocol. Starting at this dose rather than titrating up is appropriate, as this is the dose used in successful clinical trials.
Infant Administration: Infant formulations are designed for ease of administration and appropriate dosing. Products like Evivo are typically mixed with a small amount of breast milk and given once daily.
Storage: Follow manufacturer instructions for storage. Refrigeration typically extends viability, though shelf-stable formulations are available. Avoid heat and moisture exposure.
Key Takeaways
Bifidobacterium infantis represents one of the most specialized and therapeutically valuable probiotic strains available. Its evolutionary adaptation to the infant gut has produced unique capabilities that translate into powerful benefits for adults with IBS and inflammatory gut conditions.
For IBS sufferers specifically, B. infantis 35624 stands as one of the most evidence-based probiotic interventions in existence. Multiple rigorous clinical trials have demonstrated significant improvements across the full spectrum of IBS symptoms, from pain and bloating to bowel dysfunction. The effective dose of approximately 1 billion CFU daily is lower than many other probiotics, and single-strain products may outperform combinations.
For infants, ensuring adequate B. infantis colonization supports healthy immune development and may have long-term implications for disease risk. The concerning decline in B. infantis populations in Western infants has prompted development of specialized infant supplements to restore this evolutionarily appropriate gut ecology.
Whether for adult IBS treatment or infant gut health, B. infantis offers targeted therapeutic potential backed by high-quality clinical evidence. Look for products containing well-characterized strains, particularly 35624 for IBS applications, and allow adequate time for benefits to develop with consistent daily use.