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Lcs5.0
L. casei Shirota Research
Mostly mechanism / observational
15 peer-reviewed studies
What the evidence says
Mostly mechanism / observational
Most L. casei Shirota studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from high-quality meta-analyses and randomised trials published 2003–2026 with a typical study size of 96 participants.
Based on 15 studies · 2 meta-analyses · 12 RCTs · 5,317 total participants
Confidence
High confidence
By outcome
Bowel habit & constipationSofter stools and less self-reported constipation severity in people who start with hard or infrequent stools; no benefit demonstrated for bloating or flatulence · 2-4 weeks
Mostly mechanism / observational6 studies
Stress & mood
Mostly mechanism / observational6 studies
Immune activation & vaccine responseFewer and shorter upper respiratory infections in working-age adults in two trials — but completely null in the largest trial, conducted in nursing-home elderly · 2-12 weeks
Mostly mechanism / observational4 studies
Respiratory infections
Mostly mechanism / observational3 studies
Sleep under stressPreservation of deep (N3) sleep and sleep latency during a period of rising psychological stress, rather than improvement in normal sleep · 8 weeks
Too few graded studies1 study
Gut microbiome diversity
Too few graded studies1 study
Antibiotic-associated diarrhoea
Too few graded studies1 study
Safety profile
Too few graded studies1 study
Active research area
7 studies in the last 5 years · Latest meta-analysis: 2026
200320142026
1Meta-Analysisn=3,154 · very large study2026
In plain English: Some probiotics or combinations may offer benefits for patients with IBS in improving QoL, depression, and anxiety; however, as this is a developing field, additional research is necessary to fully understand the effectiveness, underlying mechanisms, and specific strains that may be advantageous.
Rokkas T et al. · European journal of gastroenterology & hepatology (2026)
In terms of improving quality of life (QoL), B. longum was the most effective (SUCRA = 89.7%), while L. plantarum was the least effective (SUCRA = 14.9%).
For alleviating depression and anxiety, the combination of probiotics (SUCRA = 95.6%) and L. acidophilus (SUCRA = 74.2%) showed the best results, respectively.
Some probiotics or combinations may offer benefits for patients with IBS in improving QoL, depression, and anxiety; however, as this is a developing field, additional research is necessary to fully understand the effectiveness, underlying mechanisms, and specific strains that may be advantageous.
In plain English: The one meta-analysis covering this strain names it explicitly as NOT increasing stool frequency, while Bifidobacterium lactis did.
van der Schoot A et al. · Clin Nutr (2022)
Probiotics overall increased stool frequency (SMD 0.71, 95% CI 0.37-1.04, p<0.00001) — but the effect was driven by Bifidobacterium lactis, 'not mixtures of probiotics, Bacillus coagulans Unique IS2 or Lactobacillus casei Shirota'
Probiotics overall improved response to treatment (57% vs 44%, RR 1.28, 95% CI 1.07-1.52, p=0.007) and integrative symptom scores (SMD -0.46, 95% CI -0.89 to -0.04)
Probiotics did not significantly improve stool consistency overall (SMD 0.26, 95% CI -0.03 to 0.54, p=0.08)
In plain English: Very long-term treatment with a Lactobacillus probiotic preparation suppressed weight loss in the elderly.
Mutoh M et al. · Nutrients (2020)
Informed consent was obtained from 237 of the 380 (62.4%) patients.
Cancer developed in 24 of 128 (18.8%) patients in the BLP extension group and 24 of 109 (22.0%) patients in the non-BLP extension group (risk ratio 0.88 [95% confidence interval 0.53-1.47]).
Although no significant difference was observed, the cumulative cancer incidence rose at a slightly lower rate in the BLP extension group.
In plain English: A Yakult-funded, multicentre, five-year trial in 359 patients reported its own null primary result.
Wong S et al. · EClinicalMedicine (2021)
PRIMARY ENDPOINT NULL: antibiotic-associated diarrhoea at 30 days 45% vs 42.1% (RR 1.071, 95% CI 0.8-1.4, p=0.639)
POST HOC subgroup: in participants regularly taking proton pump inhibitors, AAD was lower at 7 days (19% vs 35.7%, RR 0.53, p=0.040) and 30 days (28% vs 52.2%, RR 0.54, p=0.015)
Under-nutrition risk independently predicted AAD (RR 1.76 at 7 days, RR 1.69 at 30 days)
Vega-Cárdenas M et al. · Beneficial microbes (2023)
We observed an increase in butyrate or propionate concentrations in the L. casei+fructans group compared to the end of the intervention (P<0.03).
A diminished level of ANGPTL4 within the L. casei+fructans group (P=0.04) was also found, but no differences when lipopolysaccharide-binding protein was evaluated.
The FFAR2+ cell frequency decreased between baseline and at the end of 6-week intervention in L. casei+inulin (P=0.02) and L. casei+fructans groups (P=0.04).
In plain English: In this pilot study, we found no statistically significant effect of LcS probiotic on CD4+ T-cell counts, CD4+/CD8+ ratio, immune activation or intestinal microbiome among HIV-infected patients on suppressive ART with poor CD4+ recovery.
Tenore SB et al. · AIDS (London, England) (2020)
Median change in CD4+/CD8+ ratio at week 6 compared with baseline was 0 (IQR -0.04 to 0.05) in the active intervention arm and -0.01 in the placebo arm (IQR -0.06 to 0.03; P = 0.671).
At week 12, the change in CD4+/CD8+ ratio was higher in the active product group compared with placebo (respectively 0.07 and 0.01), but this difference failed to reach statistical significance (P = 0.171).
Finally, we found no statistically significant differences between groups in the change of enteric microbiome at week 12.
In plain English: Although placebo effect cannot be ignored in intervention for VM patients, the probiotic LcS still exhibits considerable efficacy against VM symptoms over a 4 month study period, supporting further clinical study of a larger and more diverse cohort.
Qi X et al. · Beneficial microbes (2020)
The secondary endpoints were anxiety and depressive symptoms, evaluated using Beck Anxiety Inventory (BAI) and Beck Depression Inventory (BDI) scores.
Efficacy of LcS over placebo was not obvious at 2 month follow-up.
Although placebo effect cannot be ignored in intervention for VM patients, the probiotic LcS still exhibits considerable efficacy against VM symptoms over a 4 month study period, supporting further clinical study of a larger and more diverse cohort.
In plain English: Under exam stress, the fermented-milk group kept significantly more gut microbial diversity and reported fewer abdominal symptoms.
Kato-Kataoka A et al. · Appl Environ Microbiol (2016)
16S rRNA sequencing showed significantly higher species number (alpha diversity) and a significantly lower proportion of Bacteroidaceae than placebo
Stress-induced increases in a visual analogue stress scale, total abdominal-dysfunction score, and the number of leukocyte genes changing more than 2-fold were all significantly suppressed
A significant pre-exam rise in salivary cortisol occurred only in the placebo group
In plain English: The strongest respiratory result in the literature — but in men only, from a Yakult-affiliated group, against plain milk rather than a matched placebo.
Shida K et al. · Eur J Nutr (2017)
URTI incidence 22.4% vs 53.2% (P=0.002); higher URTI-free rate over the period (log-rank chi-square 11.25, P=0.0008)
Fewer cumulative URTI episodes, fewer cumulative symptom days per person, and shorter duration per episode
Inhibited the reduction in NK cell activity and the rise in salivary cortisol seen in the control group
In plain English: A recent US trial improved stool consistency — but it was open-label with a no-treatment control, so expectancy is unblinded.
Cook CM et al. · J Nutr (2025)
PRIMARY ENDPOINT MET: significantly lower proportion of participants with hard or lumpy stools in 25% or more of bowel movements (OR 0.34, 95% CI 0.14-0.80, P=0.014)
Higher proportion with reduced frequency of hard-stool bowel movements from baseline (OR 2.86, 95% CI 1.03-7.92, P=0.043)
Improved total PAC-QOL constipation quality-of-life scores (P=0.003)
In plain English: A second office-worker trial reporting fewer and milder respiratory infections, with dendritic-cell activation as the proposed route.
Naito T et al. · Biosci Microbiota Food Health (2025)
Significantly lower incidence and severity of URTIs than the control milk group, with suppression evident after 14 days
HLA-DR expression higher on conventional dendritic cells and monocytes at days 14 and 28; CD86 higher on dendritic cells at day 14
Among interferon-positive participants, serum IFN-alpha2 was higher in the probiotic group at day 28