Know2eat

Lactobacillus casei Shirota

Lacticaseibacillus paracasei strain Shirota

Probiotics & Gut

What lactobacillus casei shirota may help with

Ranked by how strong the human evidence is — best supported first.

Best supportedImmune functionLimited evidence· 4 sources

Then, in order

About Lactobacillus casei Shirota

The strain isolated by Minoru Shirota in the 1930s and sold since in a small fermented milk drink. Each bottle typically contains at least 6.5 billion CFU.

The Shirota strain has a large literature and an unusual problem with it: an overwhelming share of the trials were conducted or funded by the company that sells it, and many are small, unblinded, or conducted in Japanese occupational cohorts with soft endpoints such as self-reported bowel movement frequency or stress questionnaires. The constipation and stool-frequency work is the most consistent. The immune and stress findings, including studies in students before examinations, are interesting and thin, and the fermented milk vehicle itself contains sugar, which the trials rarely control for.

Sold as
Fermented milk drink, Capsule
Standardised to
At least 6.5 billion CFU of strain Shirota per 65 ml bottle in the standard product — a product without this marker may not resemble what was studied.
Also known as
LcS, Shirota strain, Yakult strain

Regulation: Sold as a food or food supplement. EFSA rejected health claim applications for this strain, so European labelling cannot state a benefit. Japanese Foods for Specified Health Uses regulation permits certain claims domestically under a different evidentiary standard.

What the research used

The amounts, forms and durations published trials of Lactobacillus casei Shirota actually administered.

These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.

  • Studied for Bowel habit and constipation

    6.5–65 billion CFU

    Limited

    One to several fermented milk bottles daily · 2–8 weeks

    Most trials used one or two bottles a day. Nearly all were conducted or supported by the manufacturer, and outcomes are self-reported stool frequency and consistency.

This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.

None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.

  • Any time

    Not enough

    The drink is usually consumed once daily at no particular time. No trial has compared timings, and the milk vehicle itself provides the buffering that aids gastric survival.

    Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.

The evidence in depth

Best supported: Limited

What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.

Immune function

Immune Health
Limited evidence

Some trials in athletes, students and older adults report fewer upper respiratory symptom days with the Shirota strain, alongside changes in natural killer cell activity. Results are inconsistent, sample sizes small and independent replication limited.

Limited evidence. Early human work, or mostly lab and animal research.

View the 4 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Bowel regularity

Gut & Digestive Health
Not enough evidence

Trials report modest increases in stool frequency and improved consistency in people with constipation. The endpoints are self-reported, the studies are mostly manufacturer-conducted, and the fermented milk itself may contribute independently of the organism.

Not enough evidence. Not enough human research to say anything useful yet.

No source is attached to this association yet, so it is rated not enough evidenceby default. It is listed because people commonly ask about it — not because there is evidence for it.

Stress and anxiety

Mental Wellbeing
Not enough evidence

Small studies in students facing examinations reported lower salivary cortisol and fewer physical symptoms. These are small, short and not independently replicated, and there is not enough evidence to support a stress claim.

Not enough evidence. Not enough human research to say anything useful yet.

View the 3 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Things to know

Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.

  • Avoid

    Immunocompromise and critical illness

    The standard live-culture contraindications apply: severe immunosuppression, critical illness, central venous catheters and recent major gastrointestinal surgery are situations for specialist advice rather than self-treatment.

  • Worth knowing

    Manufacturer-conducted evidence base

    A very large share of the trials on this strain come from the company selling it. That does not make them wrong, but independent replication is the missing ingredient and EFSA declined the corresponding health claims.

  • Worth knowing

    Sugar in the drink vehicle

    The standard fermented milk product contains added sugar in a small volume. Someone drinking several bottles a day for a bowel effect is also drinking the sugar, which the trials generally did not control for.

  • Allergy

    Dairy

    The drink is a milk product and is unsuitable for milk allergy; it contains only small amounts of lactose after fermentation.

Evidence ratings on this page: 1 limited evidence, 2 not enough evidence.

Supplements are sold in the US without pre-market review of efficacy or safety. Nothing on this page is a recommendation to take Lactobacillus casei Shirota, or a dose to follow.