Gastroenteritis and lactose intolerance: what to know

The lining of the small intestine can be irritated during gastroenteritis. This may reduce lactase, the enzyme that breaks down lactose, for a period after the infection. Undigested lactose reaches the colon, where bacteria ferment it and draw in water. Bloating, gas, cramping and loose stools may then follow milk, ice cream or other dairy foods. This pattern is different from a milk-protein allergy, which can cause allergic symptoms such as hives or swelling.

Prioritise fluids and gentle foods while vomiting or diarrhoea is active. If dairy clearly worsens symptoms, reduce it for a short period and choose calcium-containing alternatives that suit you. Lactose-free milk or yoghurt may be easier to tolerate. Reintroduce small portions gradually as your bowel symptoms improve rather than avoiding all dairy indefinitely. A food diary can connect specific portions with symptoms. Nutrition Counselling can help prevent unnecessary restriction, especially for children or people with a limited diet.

Seek medical advice if diarrhoea persists, symptoms occur without dairy, weight is falling, there is blood in the stool, fever is significant, or you cannot maintain fluids. Urgent help is needed for severe dehydration, fainting, confusion, severe abdominal pain or repeated vomiting. A clinician may consider Food Intolerance Testing or other evaluation when the pattern does not settle after recovery.

Ask how long a temporary reduction in lactose is reasonable, which foods can replace calcium, whether the symptoms fit Lactose Intolerance, and whether another condition should be checked. Bring your food-and-symptom diary and describe the original infection and its recovery.