Lactulose

Lactulose is a synthetic sugar used as a prebiotic and laxative. It promotes the growth of beneficial gut bacteria, improves bowel regularity, and is medically used to treat constipation and reduce blood ammonia levels in liver disease.

A synthetic disaccharide; human body does not digest it; fermented in colon by bacteria; often used therapeutically (e.g. treating constipation, hepatic encephalopathy).