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Milk may have suited you before a stomach bug, yet seem harder to tolerate afterwards. Temporary lactose intolerance is one possible explanation. It does not mean everyone needs to stop dairy after gastro, or that a new symptom proves lactose is the cause.
Why tolerance can change
Lactase is the enzyme that breaks down lactose, the sugar in milk. It works in the small intestine. An infection that affects the intestinal lining can reduce lactase activity, leaving more lactose undigested. This is called secondary lactase deficiency. It can improve as the intestine recovers, although the timing varies.
Gas, bloating, cramps and diarrhoea can occur when lactose is not well tolerated, but these symptoms overlap with other conditions. Ongoing infection and other problems need consideration too. Avoid deciding that all symptoms after gastro are a permanent food intolerance.
Do not turn a possibility into a blanket ban
A temporary difficulty with lactose is different from cow’s-milk protein allergy. Lactose-free dairy still contains milk proteins. Our guide to lactose-free and dairy-free labels explains that distinction.
If a clinician recommends a short-term lactose adjustment, ask what to change, how long to try it and when to review tolerance. Smaller amounts or suitable lactose-free dairy may provide options. Cutting out every dairy food indefinitely can make meeting nutrient needs harder. Our calcium food guide can help you discuss replacements with a dietitian.
Children need their own advice
The Royal Children’s Hospital guideline does not recommend routine lactose restriction for children with gastroenteritis. It may be considered when stool frequency increases. Continue breastfeeding, and seek clinical advice before changing an infant’s formula or restricting a child’s diet. Once rehydrated, children can generally return to their usual diet, guided by their treating team.
Make the review useful
For a non-urgent appointment, record when the illness started, whether symptoms are settling, and the foods, amounts and timing involved. Include medicines and any previous milk allergy or gut diagnosis. A brief food and symptom diary is more useful than testing several exclusions at once.
Get medical advice for persistent or worsening symptoms, blood in stools, severe pain, dehydration or difficulty keeping fluids down. Seek advice earlier for infants or anyone medically vulnerable. Do not wait for a diet trial to solve an acute illness.