Lactose Intolerance in Irritable Bowel Syndrome: Prevalence, Subtype Correlations, and Clinical Predictors in an Indian Cohort.

Irritable bowel syndrome (IBS) and lactose intolerance (LI) frequently coexist, complicating diagnosis and management due to overlapping abdominal pain, bloating, and altered bowel habits. This study aimed to quantify LI prevalence in IBS and delineate clinical predictors to inform targeted care. We conducted a single-center observational study (July 2021-December 2022) at a tertiary hospital in North India, enrolling 100 adults with Rome IV-defined IBS. Standardized hydrogen breath testing identified lactose malabsorption; demographic, dietary, and symptom data were collected, and associations were evaluated using chi-square tests and logistic regression with a prespecified α = 0.05.  LI was present in 38 (38%) IBS patients in this study. The diarrhea-predominant (IBS-D) subtype showed the strongest association with LI (OR = 5.92; 95% CI 2.1-16.8; p < 0.001), whereas the constipation-predominant (IBS-C) subtype was least affected. Higher habitual lactose intake (≥26 g/day) correlated with greater symptom frequency (p < 0.001). The cohort's mean age was 36.8 ± 11.4 years, and most reported symptoms for ≥1 year, underscoring chronicity. No significant associations were observed with sex or BMI categories.  These findings demonstrate that unrecognized LI contributes substantially to symptom burden in Indian IBS populations, particularly IBS-D. Incorporating structured dietary assessment and selective breath testing into diagnostic algorithms can reduce misclassification, avoid unnecessary pharmacotherapy, and enable individualized lactose restriction. The study provides population-specific evidence supporting diet-responsive, precision strategies for IBS care and highlights the value of simple, noninvasive diagnostics in resource-constrained settings. Prospective multicenter trials integrating microbiome and dietary interventions are warranted to refine subtype-specific, nutrition-based management.