Dietary fiber may help to regulate normal defecation by

• A. increasing stool weight and bulk
• B. inhibiting the growth of colonic bacteria
• C. reducing incidence of constipation
• D. removing water from the colon

Answer: (A)

Dietary fiber helps regulate defecation primarily by increasing stool weight and bulk. Fiber resists digestion and adds undigested material to the stool, and many fibers also hold water, expanding stool mass. This bulk stretches the colon walls, stimulates peristaltic activity, and speeds transit, making bowel movements more regular. While soluble fiber can soften stool by water retention and colonic fermentation can influence gut bacteria, the direct mechanism for normal defecation is the increase in stool weight and bulk. Removing water from the colon or inhibiting colonic bacteria aren’t how fiber promotes regularity, and while a lower incidence of constipation can result, the operative effect is the expanded stool mass.