Giardia and lactose intolerance

The lining of the small intestine produces lactase, the enzyme that breaks down lactose in milk. Giardia can irritate this lining, so lactase activity may fall during recovery. Undigested lactose draws water into the bowel and is fermented by gut bacteria, which can produce abdominal pain, bloating, wind and diarrhoea. This pattern does not prove a lasting intolerance or a continuing parasite infection. Symptoms may also come from the original illness, another food sensitivity, or a different bowel condition.

Keep a brief food-and-symptom record and discuss a short, structured reduction of lactose with a clinician or dietitian. Choose naturally lactose-free alternatives that provide calcium and protein, and read labels because lactose can occur in prepared foods and medicines. Some people tolerate small portions, yoghurt, or hard cheese better than a large glass of milk, but responses vary. Avoid removing all dairy for a long period without a replacement plan. Nutrition counselling can help protect intake while the bowel settles.

Arrange assessment if diarrhoea continues despite dietary changes, symptoms wake you at night, weight is falling, or pain is persistent. Seek urgent care for severe weakness, fainting, blood in stool, repeated vomiting, or very little urine. A clinician may review the original giardia diagnosis, consider other causes, and decide whether food intolerance testing or another evaluation is appropriate.

Ask how long a lactose reduction should last, which foods can replace calcium and protein, whether your symptoms fit post-infectious intolerance, and whether testing is useful. Share your usual diet, symptom timing, medicines, and any ongoing diarrhoea.