Lactobacillus species are used to support lactose intolerance primarily on the basis of scientific validation. Multiple well-controlled studies have demonstrated that certain strains of Lactobacillus (notably L. acidophilus and L. bulgaricus) can help alleviate symptoms of lactose intolerance. These bacteria are capable of producing the enzyme beta-galactosidase (lactase), which breaks down lactose into glucose and galactose, making it easier for individuals with lactase deficiency to digest dairy products.

Clinical trials have shown that consuming yogurt or fermented milk products containing live Lactobacillus cultures improves lactose digestion and reduces gastrointestinal symptoms such as bloating, cramps, and diarrhea in lactose-intolerant individuals. The effect is attributed to the bacteria's ability to survive gastric transit and deliver lactase activity directly in the small intestine. A 2010 meta-analysis published in the Journal of Dairy Science concluded that probiotics with lactase activity, especially Lactobacillus strains, significantly improve lactose digestion.

While not all Lactobacillus strains have the same efficacy, and effects can be strain-specific, the overall evidence base is robust. The use of these probiotics is now a recommended adjunct or alternative to dietary lactose restriction or enzyme supplementation in mild to moderate cases of lactose intolerance.