Lactobacillus (usually provided as a mixed-species probiotic supplement) is broadly supported by scientific evidence for its role in supporting the health of the large intestine (colon). Numerous randomized controlled trials and meta-analyses have demonstrated that certain strains of Lactobacillus can help maintain a healthy balance of gut microbiota, improve symptoms of some gastrointestinal disorders, and support the integrity of the intestinal barrier. For example, Lactobacillus rhamnosus GG and Lactobacillus acidophilus have been studied for their role in reducing antibiotic-associated diarrhea and the recurrence of Clostridioides difficile infection. Other research highlights benefits in managing symptoms of irritable bowel syndrome (IBS), such as bloating and irregular bowel movements, although effects can be strain-specific and vary by individual.

The mechanism of action includes competitive inhibition of pathogenic bacteria, production of short-chain fatty acids (which nourish colon cells), and modulation of the immune response within the gut. While not all mixtures of Lactobacillus species have been studied in every condition, and the efficacy can depend on the specific strains and doses used, the overall scientific consensus is that Lactobacillus probiotics can support colonic function and health. Thus, use of mixed Lactobacillus as a supplement for large intestine support is scientifically justified, though not all benefits are universal or guaranteed for every person.