Final answer:
Fiber, particularly insoluble fiber, decreases gastric emptying because undigested fiber adds bulk, which slows down the movement of chyme through the small intestine. Soluble fiber also slows down gastric emptying but through a different mechanism, forming a gel-like substance in the digestive tract.
Step-by-step explanation:
If fiber is present in the stomach, it generally decreases gastric emptying. This is because the enzymes that digest cellulose cannot bind to the cellulose due to altered active sites; as a result, undigested fiber adds bulk to the food which can ease bowel movements. Fiber, particularly insoluble fiber, adds to the volume of stomach contents, which can stimulate cells in the stomach to secrete digestive juices in preparation for incoming food. However, the undigested bulk of fiber can also slow the movement of chyme through the small intestine, effectively slowing down gastric emptying.
Soluble fiber may also have an effect on gastric emptying by forming a gel-like substance that slows the movement of the chyme. This type of fiber can be classified as a carbohydrate, is essential for healthy digestion, and plays a role in the movement of food wastes through the large intestine.