Can lactose intolerance cause constipation?

Constipation is not usually associated with lactose intolerance, a condition where the gut cannot process a sugar in milk called lactose. However, lactose intolerance frequently causes diarrhea, bloating, flatulence and abdominal cramping.

When someone has lactose intolerance, their small intestine does not produce enough lactase, the enzyme that digests lactose. Instead, lactose has to be broken down by bacteria that live in the large intestine. This process produces gas and other by-products, leading to the unpleasant symptoms of lactose intolerance such as bloating, abdominal pain, flatulence and diarrhea. 

If you’re constipated, it’s best to discuss the issue with your healthcare provider to make sure that the constipation is not being caused by another health condition, such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), diverticulosis or thyroid disease. Constipation is common and can sometimes be remedied with lifestyle changes, such as drinking plenty of fluids, getting enough fiber from your diet and exercising regularly. Some over-the-counter constipation relief products, including fiber supplements and stool softeners, may help as well.

Symptoms of lactose intolerance can be managed by limiting or avoiding milk products, eating lactase-fortified foods or taking lactase supplements.

Updated by Julie McDaniel, MSN, RN, CRNI, August 2024.