What should you know about primary lactose intolerance?

Lactase breaks down lactose, the natural sugar in milk. When less lactase reaches the intestine, undigested lactose draws in fluid and is fermented by gut bacteria. This may lead to bloating, cramping, abdominal pain, gas or diarrhoea after milk, ice cream, soft cheese or other dairy foods. Primary intolerance develops from a gradual reduction in lactase rather than an allergy; it does not mean every dairy food must be avoided.

Keep a food-and-symptom diary to look for a repeatable pattern. Many people tolerate small portions with a meal better than a large serving alone. Lactose-free milk, yoghurt with live cultures and hard cheeses may be easier to digest. If you reduce dairy, protect calcium and vitamin D intake with suitable fortified alternatives or advice from a nutrition professional. Food intolerance testing may be discussed when the pattern is unclear or symptoms continue.

Arrange a clinical review for persistent diarrhoea, unexplained weight loss, blood in stool, repeated vomiting, fever, night-time symptoms or pain that is severe or worsening. Swelling of the lips or face, wheezing or trouble breathing after food suggests an allergic reaction and needs urgent help. A clinician can consider other causes of bowel symptoms rather than assuming lactose is responsible.

Ask whether your symptom timing fits lactose intolerance, whether another bowel condition should be considered, and how to test a temporary lactose reduction safely. Discuss which dairy alternatives meet your nutritional needs and whether a dietitian referral would help.