AKT · Gastroenterology/Small bowel & malabsorptionlow yield

Lactose intolerance

Lactase deficiency → osmotic/fermentative diarrhoea on dairy

Overview

Inability to digest lactose from reduced intestinal lactase — primary (genetically programmed decline, common in non-European ancestry) or secondary (transient, after gastroenteritis/coeliac/Crohn damaging the brush border). Lactose ingestion causes bloating, cramps, flatulence and watery (osmotic) diarrhoea. Diagnosed clinically/with a hydrogen breath test; managed by reducing lactose.

Recognise

Bloating, abdominal cramps, flatulence and watery diarrhoea within hours of dairy/lactose
Symptoms dose-related to lactose; resolve on a low-lactose diet
Primary (adult-onset, ethnic) or secondary (post-gastroenteritis/coeliac — recovers as the mucosa heals)

Red flags

Weight loss/anaemia/blood → not simple lactose intolerance; investigate (coeliac, IBD)
Secondary cause (coeliac/IBD) underlying

Differentials & how to tell them apart

Irritable bowel syndromesymptoms not limited to dairy; normal lactose testing

Coeliac diseasepositive serology, weight loss/anaemia — and a cause of secondary lactase deficiency

Cow's milk protein allergyimmune-mediated (esp. infants), can be IgE-mediated

Investigations

Clinical (symptom-diet relationship); hydrogen breath test or lactose tolerance test; trial of lactose exclusion. Exclude coeliac if features suggest.

Management

Reduce dietary lactose (± lactase supplements); treat any secondary cause

1Confirm the dairy-symptom relationship (± breath test). Reduce dietary lactose; ensure calcium/vitamin D intake; lactase supplements as needed.Gate: Exclude a SECONDARY cause (coeliac, IBD, post-gastroenteritis) — secondary lactase deficiency recovers once the underlying mucosal disease is treated/healed
2Dietary management; treat any underlying cause; reassess secondary cases after recovery.

Reduce dietary lactose; lactase supplements — low-lactose/lactose-free products; calcium/vitamin D adequacy

Key points

Dairy-related bloating/cramps/watery diarrhoea = lactose intolerance → reduce lactose. Look for a secondary cause (coeliac/post-gastroenteritis) that's reversible.

Monitor & prognosis

Symptoms; calcium intake.

Good with dietary control.

Source: BSG; CKS