How effective is food intolerance testing for lactose intolerance?

Lactose intolerance happens when the small intestine does not make enough lactase to digest lactose, the sugar in milk. Undigested lactose can draw water into the bowel and be fermented by gut bacteria, causing bloating, wind, cramps or loose stools after dairy. A hydrogen breath test can look for this digestive process after lactose is consumed. A clinician may also use a careful dietary trial and symptom review. Some commercial panels marketed as food intolerance tests do not directly measure lactose digestion, so a positive result may not explain your symptoms.

Keep a short diary of dairy foods, portion sizes, timing and symptoms before testing. Do not remove all dairy for a long period without advice, because calcium and vitamin D intake may fall. Your clinician can help distinguish lactose intolerance from milk allergy, coeliac disease, irritable bowel syndrome or another cause of abdominal symptoms. If lactose is the trigger, reducing the amount, choosing lactose-free products or using lactase products may help while preserving a balanced diet.

Arrange medical assessment for persistent diarrhoea, vomiting, unexplained weight loss, blood in the stool, fever, severe abdominal pain or symptoms that wake you at night. Seek urgent help for swelling of the lips or throat, breathing difficulty, faintness or widespread hives after milk, because these can indicate an allergic reaction rather than lactose intolerance.

Ask which test fits your symptoms, whether you should prepare by changing your diet or medicines, and how to maintain calcium intake during a trial. You can also ask how long to track symptoms and what would suggest another diagnosis.