Lactose, the natural sugar found in milk products, is digested in the small bowel by means of the enzyme lactase. About 10% of adults in the United States are lactose intolerant meaning they do not have enough lactase to digest ingested lactose. When they eat milk or milk products (that contain lactose), they develop crampy abdominal pain, bloating, and diarrhea.

While not one of the most common gastric bypass side effects, lactose intolerance can be acquired after gastric bypass in a small percentage of patients. When a person with a normal stomach drinks milk, it accumulates in the stomach and then is released slowly into the small intestine. There is enough lactase available to handle a small amount of milk at a time.

After gastric bypass, milk passes directly through the gastric pouch into the small bowel at a much higher rate. The milk can overwhelm the available enzyme (lactase) and the lactose intolerance symptoms occur, leading to lactose intolerance as one of the side effects of bariatric surgery. The strategies to deal with lactose intolerance that develops as one of the gastric bypass side effects you experience will be to take milk products more slowly, eat thicker products such as yogurt or cheese rather than liquid milk, potentially avoid milk products altogether, or take an enzyme substitute Lactaid with meals.

Adjusting your diet after gastric bypass is one of many important lifestyle changes which may be required. While lactose intolerance isn’t one of the most common gastric bypass side effects, there’s certainly a possibility it could occur for you, and you should be aware of what that may entail.

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