Evidence supporting the use of: Bacillus subtilis
For the health condition: Small Intestinal Bacterial Overgrowth

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Synopsis

Source of validity: Scientific
Rating (out of 5): 2

Bacillus subtilis is a spore-forming probiotic that has attracted scientific attention for its potential role in addressing Small Intestinal Bacterial Overgrowth (SIBO). While traditional use of B. subtilis is limited—most probiotic traditions focus on lactic acid bacteria—scientific studies have begun to explore its utility in gut health, including SIBO. The justification for its use is primarily scientific, although the evidence remains limited and preliminary (hence the rating of 2 out of 5).

The rationale for using B. subtilis in SIBO revolves around its ability to modulate the gut microbiota, suppress pathogenic bacteria, and support mucosal barrier function. In vitro and animal studies have shown that B. subtilis can inhibit the growth of harmful bacteria through the production of antimicrobial compounds (such as bacteriocins) and competitive exclusion. A handful of small human clinical trials and case reports suggest that B. subtilis, alone or in combination with other probiotics, may reduce gastrointestinal symptoms (such as bloating and diarrhea) and improve gut microbiota composition in individuals with SIBO or similar dysbiosis.

However, well-powered, placebo-controlled clinical trials specifically addressing B. subtilis in SIBO are lacking. Most available studies include B. subtilis as part of multi-strain probiotic formulations, making it difficult to attribute benefits solely to this species. Overall, while mechanistic and early clinical data are promising, more high-quality research is needed before B. subtilis can be considered a fully evidence-based treatment for SIBO.

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