Drinking milk and getting diarrhea – is it lactose intolerance?

Many people experience diarrhea after consuming milk or dairy products, which may be a sign of lactose intolerance.

What causes lactose intolerance?

The carbohydrates in milk primarily consist of lactose, a disaccharide composed of one glucose and one galactose molecule. To be absorbed, lactose must be broken down into glucose and galactose by an enzyme called "lactase" in the small intestine. "Lactose intolerance" occurs when there is a deficiency or reduction in lactase activity in the small intestine. In such cases, lactose cannot be properly digested and instead, undigested lactose is fermented by intestinal bacteria, leading to the production of substances that can cause diarrhea. Consequently, individuals may experience symptoms such as abdominal pain, increased gas, or diarrhea after consuming milk or dairy products.

Lactose intolerance can be congenital, but in most cases, it develops later in life.

As individuals age, the activity of lactase tends to decrease, making them more susceptible to lactose intolerance. The prevalence of lactose intolerance varies among different ethnicities, with it being more common in Asian populations.

Sometimes, temporary lactose intolerance can occur, especially after gastrointestinal illnesses like diarrhea. This is a transient condition resulting from the incomplete repair of the small intestine's mucosa. Typically, this temporary lactose intolerance resolves on its own within 1-2 weeks.