Step 1: Understanding the Concept:
Dietary fiber consists of the non-digestible parts of plant foods. Humans do not have enzymes to break down fiber for energy.
Step 2: Detailed Explanation:
1. Bulk and Motility: Fiber adds bulk to the stool and absorbs water. This softens the stool and speeds up its passage through the intestines, thereby preventing constipation.
2. Gut Health: Insoluble fiber acts as a "broom" for the intestines, while soluble fiber acts as a prebiotic, feeding healthy gut bacteria.
3. Blood Sugar: Fiber actually slows down the absorption of sugar (helps manage diabetes), unlike Option A.
Step 3: Final Answer:
The primary physiological benefit of dietary fiber is the maintenance of regular bowel movements and overall digestive health.