Private lactose intolerance clinic in London, same-day gastroenterology.

Intolerance or allergy?

• Lactose intolerance — a digestive problem. The enzyme lactase is reduced, so lactose ferments in the colon producing gas. Symptoms come on 30 minutes to a few hours after dairy: bloating, wind, cramps, rumbling and loose stools. Dose-dependent — a splash of milk in tea is usually fine, a large latte is not.
• Cow's milk allergy — an immune reaction to milk protein. Can cause hives, swelling, wheeze and anaphylaxis, and is far more common in infants than adults. Even tiny amounts matter.
• Confusing the two leads to unnecessary avoidance on one hand and dangerous exposure on the other.

Secondary lactose intolerance

Lactase lives on the tips of the intestinal lining, so anything damaging that lining causes temporary intolerance — gastroenteritis, coeliac disease, Crohn's disease, or a course of antibiotics. This usually recovers over weeks to months once the underlying problem settles. If intolerance appears suddenly in an adult, it is worth looking for a cause rather than simply cutting out dairy — coeliac disease in particular presents this way.

Confirming it

• Often diagnosed by a trial of exclusion for two weeks followed by reintroduction — simple, free, and usually conclusive.
• A hydrogen breath test confirms it objectively where the picture is unclear.
• Coeliac screening should be done first, while you are still eating gluten, since it commonly presents identically.
• Keeping a food and symptom diary for two weeks is more useful than any commercial intolerance test.
• IgG food intolerance tests sold online have no scientific validity and routinely produce long lists of foods to avoid, which does harm.

How much you can have

Most people with lactose intolerance tolerate around 12g of lactose — roughly a glass of milk — in a day if it is spread out. Lactase enzyme tablets taken with dairy work well and allow occasional flexibility.

Calcium

This is the reason not to cut dairy out entirely without need. Adults need around 700mg of calcium a day, more in some circumstances. Good non-dairy sources include fortified plant milks (choose fortified ones — organic versions often are not), tinned fish with bones, tofu set with calcium, leafy greens such as kale and pak choi, almonds and fortified breads. Vitamin D matters alongside for absorption.