Research project led by Bailey Hanna, MS, RDN - no affiliate links, ads or sponsored products.
Bifidobacterium longum 35624, previously known as Bifidobacterium infantis 35624, is a probiotic often recommended for managing irritable bowel syndrome (IBS). There have been three randomized placebo-controlled trials (RCTs)(1)(2)(3) and two open-label trials investigating this strain in IBS populations.(4)(5) Given the significant placebo response in IBS, our evaluation focused solely on the three RCTs with a placebo control.
Key Takeaways
Clinicians Notes:
References:
Evaluate products based on whether they transparently disclose all ingredients and their amounts, exclusively use probiotics tested in randomized placebo-controlled trials in IBS populations, and contain studied doses.
This probiotic has higher quality studies in IBS populations supporting it. View our evidence evaluation framework to learn how we assess the quality of studies.
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Efficacy of an encapsulated probiotic Bifidobacterium infantis 35624 in women with irritable bowel syndrome
Am J Gas-troenterol 2006;101(7):1581–90
ADULTS Female 18-65 years
Fecal excretion of Bifidobacterium infantis 35624 and changes in fecal microbiota after eight weeks of oral supplementation with encapsulated probiotic
Gut Microbes, 4:3, 201-211
ADULTS 20-65 years
Lactobacillus and bifidobacterium in irritable bowel syndrome: symptom responses and relationship to cytokine profiles
Gastroenterol 2005;128(3):541–51
ADULTS 18-75 years
For “urgency” there was no statistically significant difference between the placebo group and the 1 million CFU/day dose. (p = 0.29)
Baseline scores for urgency for the 100 million CFU/day dose decreased by 0.54 points on a 6-point scale which was not statistically significant compared to placebo (p<0.09).
There was no statistically significant difference between the placebo group and the 10 billion CFU/day dose for urgency (p = 0.71)
For incomplete evacuation, there was no statistically significant difference between the placebo group and the 1 million CFU/day dose (p = 0.69). There were also no significant differences between these groups for the symptom of “straining” (p=0.19)
For the 100 million CFU/day dose, baseline scores for incomplete evacuation decreased by 0.54 points on a 6-point scale, a statistically significant change compared to the placebo group (p<0.04). We independently calculated an effect size of 0.31 for this parameter, classifying it as a low magnitude of effect. Similarly, baseline scores for straining decreased by 0.38 points, also statistically significant compared to placebo (p=0.02), with an effect size of 0.36, indicating a low magnitude of benefit.
There was no statistically significant difference between the placebo group and 10 billion CFU/day dose for incomplete evacuation (p = 0.34). For straining, there was also no statistically significant difference between the placebo group and the 10 billion CFU/day dose (p=0.89).
There was no statistically significant difference between the placebo group and the 1 million CFU/day dose for bowel habit satisfaction (p = 0.39)
For the 100 million CFU/day dose, baseline scores for bowel habit satisfaction decreased by 0.55 points on a 6-point scale, which was statistically significant compared to the placebo group (p<0.02). We independently calculated an effect size of 0.34 for this parameter, categorizing it as a low magnitude of effect. Notably, there was a significant increase in bowel movement frequency for those treated with Bifidobacterium infantis 35624 who had lower frequencies at baseline (10th and 15th percentiles). Conversely, there was a reduced frequency for those who had higher frequencies at baseline (81st, 88th, 90th percentiles).
There was no statistically significant difference in bowel habit satisfaction between the placebo group and the 10 billion CFU/day dose (p = 0.39).
For overall assessment of IBS symptoms, there was no statistically significant difference between the placebo group and the 1 million CFU/day dose (p = 0.63). For global assessment of IBS relief, there was no statistically significant difference between the placebo group and the 1 million CFU/day dose (p = 0.80)
For the 100 million CFU/day dose, for “overall assessment of IBS symptoms,” the probiotic produced a relative mean therapeutic gain from baseline of 30.2%, which was significant compared to the placebo group (p=0.01). We independently calculated an effect size of 0.36 for this parameter. For the “composite score,” the probiotic produced a 29.5% relative mean therapeutic improvement from baseline, also statistically significant compared to placebo (p=0.02), with an effect size of 0.35. On average, 62.3% of participants reported “yes” for global assessment of IBS relief, a statistically significant result (p=0.02), with an effect size of 0.34. All effect sizes calculated for global IBS symptoms parameters fell within our low magnitude of effect category, below 0.5.
For overall assessment of IBS symptoms, there was no statistically significant difference between the placebo group and the 10 billion CFU/day dose (p = 0.76). For global assessment of IBS relief, there was no statistically significant difference between the placebo group and the 10 billion CFU/day dose (p = 0.51)
For abdominal pain/discomfort, there was no statistically significant difference between the placebo group and the 1 million CFU/day dose (p = 0.24). For global assessment of pain relief 43.2% ± 6.1% of people in the probiotic group reported “yes” but this was not significant compared to placebo (p=0.29)
For “Abdominal pain/discomfort,” for the 100 million CFU/day dose, the probiotic produced a relative mean therapeutic improvement in symptom scores of 38.4%, which was statistically significant compared to the placebo group (p=0.03). We calculated an effect size of 0.31 for this parameter, categorizing it as a low magnitude of effect. For the “global assessment of pain relief,” 58.8% ± 6.0 of participants in the probiotic group reported “yes,” but this was not statistically significant compared to placebo (p=0.36), with an effect size of 0.12.
For abdominal pain/discomfort, there was no statistically significant difference between the placebo group and the 10 billion CFU/day dose (p = 0.44). For global assessment of pain relief 39.1 ± 6.0 of people in the probiotic group reported “yes” but this was not significant compared to placebo (p=0.11)
For bloating/distention, there was no statistically significant difference between the placebo group and the 1 million CFU/day dose (p = 0.54)
For the 100 million CFU/day dose, baseline scores for bloating and distention decreased by 0.74 points on a 6-point scale, a statistically significant change compared to the placebo group (p<0.05). We independently calculated an effect size of 0.27 for this parameter, categorizing it as a low magnitude of effect.
There was no statistically significant difference between the placebo group and the 10 billion CFU/day dose probiotic group for bloating and distention scores.(p = 0.43)
For “passage of gas,” the probiotic produced an 8.9% symptom score improvement from baseline. The placebo had a therapeutic gain over the probiotic of 3.9% (p =0.47). This result is for the 1 million CFU/day dose group.
For the 100 million CFU/day dose, baseline scores for passage of gas decreased by 0.54 points on a 6-point scale, which was statistically significant compared to the placebo group (p<0.04). We calculated an effect size of 0.28 for this parameter, categorizing it as a low magnitude of effect.
For “passage of gas,” there was no statistically significant difference between the placebo group and 10 billion CFU/day dose (p = 0.63)
No data
The study reported, “there was no significant change in the quality of life or HAD scores with any of the probiotic dosages in comparison to placebo.”
1m – A post-hoc analysis was not conducted in the IBS-C, IBS-D and “IBS-A” subtype for this probiotic dose, with this dose producing overall insignificant effects across all assessed subtypes.
100m – There was a statistically significant improvement for abdominal pain/discomfort and bowel habit satisfaction in n=18 IBS-C participants. Assessed parameters without a statistically significant improvement in IBS-C included: bloating/distention, urgency, incomplete evacuation, straining, passage of gas, overall assessment of IBS symptoms, and composite score. Therefore, the probiotic produced a neutral effect for the majority of assessed symptoms in IBS-C. There was a statistically significant improvement for incomplete evacuation, straining, bowel habit satisfaction, overall assessment of IBS symptoms, and composite score in n=49 IBS-D participants. Assessed parameters without a statistically significant improvement in IBS-D participants included: abdominal pain/discomfort, bloating/distention, urgency, and passage of gas. There were no statistically significant improvements for any symptom parameter in the “IBS-A” group of n=18 participants
10b – A post-hoc analysis was not conducted in the IBS-C, IBS-D and “IBS-A” subtype for this probiotic dose, with this dose producing overall insignificant effects across all assessed subtypes.
For the 1 million CFU/day dose group, -The randomization procedure was not described. -The study was described as double blind, though 70% of participants in the group that showed effects guessed correctly that they were in the intervention group, compared to 46% in the placebo. There was no data on the links between outcome and attrition. The study used least squares mean, but did not report standard deviations, which we had to recalculate.
No additional data/notes for the 100 million CFU/day dose.
There was a presumed formulation problem in the 10 billion CFU/day dose, which may have impaired the capsule’s ability to release its contents at this dose. Findings from this arm of the study were disqualified.
For the symptom score for “urgency” the probiotic led to an 18% relative mean score reduction from baseline at week 8. This was not statistically significant compared to placebo. (p=0.287)
For “incomplete evacuation” mean symptom scores improved by 21.0% by week 8 but this was not statistically significant compared to placebo (p=0.611); for straining, the probiotic led to a relative mean 20.7% symptom score reduction by week 8 which was also not statistically significant compared to placebo (p=0.965)
For “overall symptom severity” the probiotic led to a 13.4% reduction in mean symptom scores from baseline till week 8. This change was not significant compared to placebo (p=0.114)
For abdominal pain, there was a 16.7% reduction in mean symptom scores from baseline by week 8. The placebo had a relative therapeutic gain over the probiotic of 14.1% but this was not statistically significant (p=0.261)
For bloating, the probiotic led to an 18.6% reduction in relative mean symptom scores from baseline till week 8; this was not significant compared to placebo(p=0.576)
For “gas” the probiotic resulted in a mean symptom score reduction of 15.1% from baseline till week 8. This was not significant compared to placebo (p=0.384)
Described as a double blind study, but no description of the blinding procedure was provided. IBS symptoms were the secondary focus of the study. The main outcome measures were objective and not of IBS symptoms. Reduction in symptoms from baseline was sometimes more pronounced in the placebo group, but all outcomes were statistically nonsignificant.
Bowel movement difficulty scores significantly improved on the Likert scale at weeks 2, 3, and 5-7 compared to placebo. The area under the curve for therapeutic response was statistically significant (p < 0.05) for the between-treatment difference after adjustment for multiple comparisons. We calculated an effect size of 0.82 for this parameter, placing it in our moderate effect category (0.5 to 1.0). There were no statistically significant improvements in bowel movement frequency or consistency.
Regarding composite scores, subjects treated with B. infantis 35624 had consistently lower scores compared to those receiving placebo throughout both the treatment phase and the entire washout phase. Of the 12 weeks evaluated using VAS scores, 10 weeks showed significantly lower scores for the treatment group compared to placebo. The only weeks without significantly lower scores were weeks 10 and 11, during the washout phase. We calculated an effect size of 0.75 for this parameter, placing it in our moderate effect category.
There was a statistically significant improvement for pain/discomfort (p<0.05) vs. placebo for weeks 1,2,4,5,and 7 on likert scores for individual weeks (>50% intervention duration). For this parameter we calculated an effect size of 0.54, placing this effect in our moderate effect size category.
Bloating scores were imbalanced between treatment groups. There was a significant reduction in bloating/distention during weeks 2,5, and 6 of the intervention (<50% of the intervention time-frame; mostly neutral effect)
“For most domains, quality-of-life scores were numerically lower than those for placebo for the patients randomized to the probiotics but reached statistical significance versus placebo during the treatment phase only for health worry for bifidobacterium (at the .05 level) and dysphoria for lactobacillus (at the .10 level)” (Degree of improvement unable to be determined due to missing study details).
The probiotic reportedly “normalized” ratios of IL-10/IL-12 to that of healthy controls. The clinical relevance of this change is unclear.
The study did not report the number of participants per group, so we assumed that the two probiotic groups and the placebo group were divided equally. We assigned the number of participants for grading purposes to be the likely number of participants in the treatment group plus the placebo group (i.e. 2/3 of 67).
There were substantial baseline imbalances between treatment groups and the study was underpowered. All participants had mild IBS symptoms. Study results may have been confounded by the malted milk delivery matrix.