Beyond Malabsorption: The Need for Symptom-Based Assessment in Suspected Lactose Intolerance. Lessons From a Test-Specific Symptom Assessment.

Background: Lactose malabsorption is commonly assumed to cause gastrointestinal discomfort, but symptoms often persist despite lactose restriction or enzyme supplementation.

Objective: This study aimed to assess symptoms following lactose ingestion, its relationship with malabsorption, and its association with fructose sensitivity and disorders of the gut-brain interactions (DGBIs).

Design: In 753 consecutive patients with DGBIs, we performed hydrogen breath tests and used the validated adult Carbohydrate Perception Questionnaire (aCPQ) to assess lactose-induced symptoms. Lactose malabsorption (LM+) was defined as a hydrogen increase of > 20 ppm. Lactose induced burdensome symptoms (LS+) were defined by a visual analogue scale (VAS) increase of > 20 mm. Fructose sensitivity was assessed in 547 patients using the same protocol.

Results: LM+ was observed in 40.9% of patients, while 55.4% reported LS+. Interestingly, 45.3% of symptomatic patients had no lactose malabsorption (LM-) and 26.0% of malabsorbers had no symptoms (LS-). LS+ were significantly more likely to exhibit fructose sensitivity (45.2% vs. 24.2% in LS-, p < 0.001). DGBIs were similarly distributed in LS+ patients with and without malabsorption. Functional dyspepsia and irritable bowel syndrome were significantly more frequent in LS+, irrespective of whether lactose was malabsorbed or not, than in those without lactose-induced symptoms (with or without malabsorption).

Conclusion: Lactose malabsorption alone is an inadequate predictor of the occurrence of symptoms, emphasizing the need for comprehensive symptom assessment beyond breath test results. This has important implications for the selection of appropriate therapies. The association between lactose and fructose sensitivity suggests a role for visceral hypersensitivity and overlapping mechanisms in symptom development.