Got a stomach ulcer or a burning gut, so you reach for a glass of milk to coat and soothe it. Doctors used to actually prescribe this, the 'milk diet', and grandparents still swear by it. Cool, smooth, soothing milk on an angry stomach. What could go wrong.
Milk gives brief relief and then makes things worse. It does coat the stomach and dull the burn for a few minutes, but milk also stimulates the stomach to pump out more acid, especially as the fat and protein digest, so you get a rebound that can leave you worse off than before. The deeper shift is in what causes ulcers. For most of the 20th century doctors blamed stress and diet and prescribed milk and bland food. Then in the 1980s Australian researchers Barry Marshall and Robin Warren showed that most peptic ulcers are caused by a bacterium, Helicobacter pylori, with anti-inflammatory painkillers being the other big culprit; Marshall famously drank a dish of the bug to prove it, and the pair won a Nobel Prize in 2005. So ulcers are usually treated with antibiotics and acid-reducing drugs, not dairy. The soothing glass of milk is a short-term comfort that picks a fight with your stomach a few minutes later.