Synopsis
Separate lactose malabsorption from clinical intolerance and milk allergy, recognise secondary mucosal disease, use breath testing or structured dietary challenge appropriately, and preserve calcium, vitamin D and dietary diversity.
- Lactase non-persistence causes reduced lactose absorption, but symptoms depend on dose, meal context, transit, colonic adaptation and visceral sensitivity; malabsorption is not identical to intolerance.
- Bloating, cramp, flatus and watery diarrhoea after lactose reflect osmotic retention and bacterial fermentation, not intestinal inflammation.
- Cow's-milk protein allergy is an immune reaction with a different history; urticaria, wheeze, angioedema or anaphylaxis needs urgent allergy assessment.
- New lactose intolerance can be secondary to coeliac disease, gastroenteritis, giardiasis, Crohn's disease or other proximal mucosal injury and may improve when the cause heals.
- A short, single-variable lactose reduction followed by reintroduction is often more useful than permanent dairy exclusion; breath testing helps when the history is unclear or restriction would be burdensome.
- Hydrogen breath tests require protocol adherence and can be confounded by methane production, SIBO, antibiotics, smoking, exercise and rapid or slow transit.
- Many people tolerate yoghurt, hard cheese or modest milk with meals; use individual thresholds rather than a zero-lactose rule.
- Broad low-FODMAP or carbohydrate restriction should be time-limited and dietitian-led, with planned reintroduction to avoid nutritional and microbiome harm.
Key red flags
Rapid hives, swelling, wheeze, vomiting, hypotension or collapse after milk protein is an immune emergency, not lactose intolerance.
Profuse diarrhoea, postural symptoms, oliguria or electrolyte disturbance requires acute assessment regardless of the suspected carbohydrate trigger.
Investigation priorities
Change lactose exposure alone for a defined short period, record symptoms, then reintroduce a measured amount in a usual meal.
Management branches
Meal-linked symptoms occur without allergy or organic alarm features.
- Quantify lactose portions and associated foods, then reduce lactose alone for a short predefined interval while maintaining calcium-rich alternatives.
- Reintroduce a measured amount with food and record symptom threshold; use breath testing if the result remains unclear or major restriction is contemplated.
- Offer tolerated yoghurt, hard cheese, lactose-free dairy or lactase enzyme rather than blanket milk-protein avoidance.
- Reassess the diagnosis if symptoms continue despite verified lactose reduction.
Key medicines
Lactase enzymeUse the product-specific oral dose with the first mouthful of a lactose-containing meal, adjusted to portion size and individual response.Products vary and do not treat milk-protein allergy or another mucosal disease. Failure should prompt review of timing, dose and diagnosis.
Colecalciferol and calcium supplementationUse dietitian and BNF-guided supplementation only when dietary intake or measured vitamin D is inadequate, accounting for age, pregnancy, renal function and bone risk.Supplements do not replace a balanced diet. Check hypercalcaemia, renal stones and interactions; severe deficiency needs a formal loading plan.