How does lactulose function as a laxative?

Lactulose functions as a laxative primarily by drawing fluid into the bowel. It is a synthetic disaccharide that is not absorbed in the intestinal tract but instead reaches the colon, where it is metabolized by colonic bacteria. This fermentation process produces organic acids, which osmotically draws water into the lumen of the colon. The increased fluid content stimulates bowel movements and softens the stools, making it easier to pass. This mechanism is particularly beneficial in managing constipation and is also used in treating hepatic encephalopathy due to its ability to trap ammonia in the colon and facilitate its elimination.

The other options do not accurately describe the primary action of lactulose. For instance, while increasing gut motility is critical in some laxatives, lactulose primarily acts through osmotic effects rather than by increasing motility directly. Enhancing fiber intake and stimulating bile secretion are not relevant to how lactulose functions as a laxative, as lactulose does not contain fiber and does not influence bile production. Thus, the correct understanding of lactulose’s action centers on its ability to draw fluid into the bowel.