Lactococcus casei is a species of lactic acid bacteria commonly used as a probiotic. Its use for supporting or treating Irritable Bowel Syndrome (IBS) is grounded in some scientific research, though the evidence is limited and not as robust as for some other probiotic strains like Bifidobacterium or Lactobacillus species. Several small clinical studies and animal models have investigated the potential benefits of L. casei in modulating gut flora, improving intestinal barrier function, and reducing inflammatory markers, all of which are relevant to IBS symptoms.

Notably, a few randomized controlled trials (RCTs) have evaluated the role of L. casei (sometimes as part of a multi-strain probiotic) in IBS patients. Some of these studies have reported modest improvements in symptoms such as abdominal pain, bloating, and stool regularity. For example, a study published in Alimentary Pharmacology & Therapeutics (2011) found that a fermented milk product containing L. casei DN-114 001 led to some improvement in global IBS symptoms over placebo. However, other studies have found minimal or no benefit, and sample sizes are typically small.

In summary, while there is some scientific evidence to support the use of Lactococcus casei for IBS, the quality and quantity of the data are limited. The overall strength of evidence is low to moderate, and larger, well-designed RCTs are needed to draw firm conclusions.