EFFECTS OF LACTOBACILLUS AND BIFIDOBACTERIUM PROBIOTICS ON GUT MICROBIAL FERMENTATION IN LACTOSE INTOLERANCE: A SYSTEMATIC REVIEW

Probiotic supplementation has emerged as a potential strategy for improving lactose intolerance by enhancing gut microbial fermentation and lactose metabolism. This systematic review evaluated the effects of Lactobacillus and Bifidobacterium probiotics on biochemical parameters, gut microbial fermentation markers, and clinical outcomes in individuals with lactose intolerance. A systematic literature search was conducted in PubMed, ScienceDirect, Wiley, Frontiers, and SpringerLink for studies published between 2015 and 2026. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, seven randomized controlled trials met the predefined inclusion criteria. Data extracted included study characteristics, biochemical parameters, gut microbial fermentation markers, assessment methods, and clinical outcomes. Probiotic supplementation was associated with reduced breath hydrogen production, increased β-galactosidase activity, enhanced abundance and persistence of Bifidobacterium, and favorable modulation of gut microbial metabolism, indicating improved lactose fermentation. Clinically, probiotics consistently reduced bloating, flatulence, diarrhea, fecal urgency, abdominal cramping, vomiting, and overall gastrointestinal symptom scores, although improvements in abdominal pain were less consistent. The magnitude of these effects varied according to probiotic strain, dosage, and intervention duration. Strains such as Lactobacillus acidophilus DDS-1 and Bifidobacterium adolescent is iVS-1 demonstrated significant clinical benefits, whereas other strains primarily improved biochemical markers without corresponding symptom improvement. Current evidence suggests that Lactobacillus and Bifidobacterium probiotics improve lactose tolerance by enhancing gut microbial fermentation, increasing microbial βgalactosidase activity, reducing hydrogen production, and modulating the gut microbiota. These microbial and biochemical changes contribute to improved lactose digestion and reduced gastrointestinal symptoms, supporting selected probiotic strains as promising adjunctive interventions for the management of lactose intolerance.