Your intestines contain a sizable population of several types of bacteria known collectively as the gut microbiota. A healthy balance of these bacteria is important for bowel health and may affect other aspects of your overall health. According to the World Gastroenterology Organization, yogurt and other foods containing certain strains of probiotic bacteria can help prevent or treat some conditions that cause diarrhea. Although yogurt is usually considered a diarrhea remedy because of its probiotic content, it can potentially cause diarrhea in some people due to other components in this food.
Lactose intolerance is the most likely cause of diarrhea associated with eating yogurt. Like all milk-based foods, yogurt contains milk sugar, or lactose. This sugar is digested by an enzyme in the small intestine called lactase. Lactose intolerance describes a decreased amount of this enzyme, which results in incomplete digestion of milk sugar. Typical symptoms of lactose intolerance include bloating, abdominal cramps, increased intestinal gas and diarrhea. If your diarrhea is due to lactose intolerance, your digestive symptoms will usually begin within a few hours of eating yogurt and culminate with one or two loose stools.
Secondary Lactose Intolerance
Lactose intolerance sometimes develops as a complication of another medical condition. This is known as secondary lactose intolerance. For example, a severe case of the stomach flu, or gastroenteritis, can temporarily decrease production of lactase in your small intestine. In this situation, you may find yogurt and other milk-based products give you diarrhea. But if you were previously able to eat dairy foods without a problem, your ability to tolerate yogurt will usually return in a week or two after your intestine heals. Cancer chemotherapy or radiation therapy to the abdomen can also cause temporary lactose intolerance. Other diseases that might cause secondary lactose intolerance include HIV/AIDS, celiac disease and cystic fibrosis.
Irritable Bowel Syndrome
Irritable bowel syndrome (IBS) is another possible cause of yogurt-related diarrhea. Although the World Gastroenterology Organization reports that some studies indicate probiotics can help relieve IBS symptoms, trigger foods differ among people with this condition. Some people with IBS are sensitive to certain types of carbohydrates called fermentable oligo-di-monosaccharides and polyols (FODMAP). The sugars lactose and fructose are FODMAPs, and both are commonly found in commercial yogurts. People with IBS and FODMAP sensitivity typically experience digestive symptoms, including diarrhea, with a variety of foods rather than just yogurt. Examples of other high-FODMAP foods that can trigger symptoms include soft cheese, sour cream, soybeans, soy milk, apples, peaches, pears, cauliflower, artichokes, beans, lentils and mushrooms.
Milk allergy is a possible cause of yogurt-related diarrhea, particularly in a young child. However, a young child with a milk allergy experiences digestive and other allergic symptoms with all milk-based foods rather than just yogurt. In addition to diarrhea -- which may be bloody -- other food allergy symptoms include vomiting, stomach cramps, hives, wheezing, difficulty breathing, and swelling of the lips, face, tongue or throat. Cow's milk allergy is usually diagnosed in the first 6 months of life and rarely after 1 year of age. Most children with cow's milk allergy outgrow it by age 5. Given the usual course of cow's milk allergy, it's unlikely -- though not impossible -- that an adult with no history of a milk allergy would suddenly develop an allergic reaction to the milk in yogurt.
Diarrhea related to eating yogurt may be a one-off situation if you've recently had the stomach flu. You can try eating it again in a few weeks. If you suspect your symptoms are related to lactose intolerance, you might try eating a smaller serving of yogurt to see if you still experience diarrhea. Most people with lactose intolerance can eat some dairy without symptoms, so eating a smaller amount might do the trick. You can also try a rice or soy yogurt since they are lactose-free. The look and texture of these yogurts is similar to milk-based yogurt, but the taste is not identical, so you might need to get used to them.
See your doctor for frequent or persistent diarrhea, especially if it is accompanied by other symptoms. Seek emergency medical care if you or your child experience symptoms of an allergic food reaction, particularly if there is breathing difficulty.