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Bacillus subtilis

Bacillus subtilis

Probiotics & Gut

What bacillus subtilis may help with

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

Best supportedDigestive comfortNot enough evidence· 4 sources

Then, in order

About Bacillus subtilis

A soil and gut-associated spore-forming bacterium, familiar from natto, the fermented soybean food. Sold in "soil-based" spore probiotic blends and as single strains such as DE111.

Bacillus subtilis is where the marketing gets ahead of the evidence most obviously. Spore products are sold on the premise that soil organisms are what humans evolved alongside and that modern hygiene removed them — a story, not a finding. Human trials of specific strains are few, small and supplier-funded, covering stool consistency, occasional immune markers and, in some cases, body composition alongside training. Some Bacillus strains also carry transferable antibiotic resistance genes or produce enterotoxins, which is why regulators evaluate them strain by strain rather than as a species.

Sold as
Capsule, Spore blend, Fermented soy food
Standardised to
CFU of the named strain, typically 1–5 billion — a product without this marker may not resemble what was studied.
Also known as
B. subtilis DE111, Natto bacillus, Spore probiotic

Regulation: Sold as a dietary supplement with no pre-market efficacy review. EFSA assesses Bacillus strains individually for the qualified presumption of safety, specifically checking for transferable antibiotic resistance and toxin production — a reminder that not every strain of this species is a benign organism.

What the research used

The amounts, forms and durations published trials of Bacillus subtilis 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 digestive symptoms

    1–5 billion CFU

    Not enough

    Capsule, daily · 4–12 weeks

    From a small number of supplier-funded trials of individual strains. Dosing for this species is not well established and results do not transfer between strains.

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

    Spores survive gastric acid without buffering, so food timing is not a survival issue. No outcome-based timing comparison exists.

    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: Not enough

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.

Digestive comfort

Gut & Digestive Health
Not enough evidence

Small trials of individual strains report changes in stool consistency and gastrointestinal symptom scores. There is not enough independent human research to support a digestive claim for this species.

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

View the 4 sources

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

Gut microbiome

Gut & Digestive Health
Not enough evidence

Spore organisms can be recovered from stool during supplementation. Evidence that they meaningfully or durably alter the resident microbial community in people is absent.

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, central lines and critical illness

    Bacillus species have caused bacteraemia and, rarely, endocarditis in vulnerable patients. Spore-based products should not be started by critically ill or severely immunosuppressed people without specialist advice.

  • Worth knowing

    Not all Bacillus strains are safe organisms

    Some strains of this genus carry transferable antibiotic resistance genes or produce enterotoxins, which is why safety assessment is done strain by strain. A product selling "soil-based organisms" without strain identification has not passed any such assessment in public.

  • Worth knowing

    The "soil organisms we evolved with" story is not evidence

    The marketing rationale for spore probiotics is a historical narrative about hygiene, not a trial result. It should be read as a hypothesis about why they might work, not as a reason to believe they do.

Evidence ratings on this page: 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 Bacillus subtilis, or a dose to follow.