Lactococcus acidophilus is actually a misnomer; the correct species commonly used in probiotic formulations and studied for gut health is Lactobacillus acidophilus. Assuming the inquiry is about L. acidophilus, there is moderate scientific evidence supporting its use for small intestine health. L. acidophilus is a lactic acid-producing bacterium naturally occurring in the human gastrointestinal tract, particularly in the small intestine. It is considered beneficial for supporting a balanced gut microbiota and may help inhibit the growth of pathogenic bacteria by producing lactic acid and bacteriocins.

Clinical trials have shown that supplementation with L. acidophilus can aid in the management of certain gastrointestinal conditions, such as antibiotic-associated diarrhea, some forms of infectious diarrhea, and symptoms of irritable bowel syndrome (IBS). Studies indicate that L. acidophilus may enhance the intestinal barrier function, modulate immune responses, and compete with harmful microbes in the small intestine. However, the evidence is not universally robust, and effects can vary depending on the strain, dose, and patient population studied.

The FDA recognizes some strains of L. acidophilus as Generally Recognized As Safe (GRAS) for use in foods and supplements. While traditional use of fermented dairy products containing L. acidophilus is widespread, scientific evidence rates as moderate (3/5) due to variability in results and the need for further high-quality human studies specifically targeting small intestine health outcomes.