What is temporary lactose intolerance?

Professor of Human Nutrition Jennie Brand-Miller explains how late-onset problems with dairy might be temporary lactose intolerance.

Q I think I’ve become lactose-intolerant. I’m in my 40s and never had any issues before, but lately I’ve been having problems when eating dairy. What’s going on?

Anna, via email

A It’s highly unlikely you’ve developed an allergy if you’ve had no issues in the past. But you may have developed temporary lactose intolerance due to a gastrointestinal infection, for example, from food poisoning.

A temporary inability to digest lactose, the sugar in milk and other dairy foods, can develop when the micro-organism causing the infection leads to the flattening of the microvilli – the tiny projections that line your small intestine. The microvilli contain the enzyme that digests lactose into sugars right before absorption. Luckily, they recover fast – usually within a week or two.

Lactose intolerance, on the other hand, is caused by an unusual immune response to a protein, rather than a sugar molecule like lactose. Dairy protein allergies that develop in young children often disappear over childhood. For people of non-European origin, however, lactose intolerance may start from late childhood. This doesn’t mean dairy foods are off the menu, as many don’t contain lactose, for example, hard yellow cheeses. Yoghurt also contains lactose, but their live cultures do an excellent job of digesting lactose for you.