Final answer:
Insoluble fiber adds bulk to the digestive system, helping to speed up the transit of food and stimulate peristalsis, thus easing bowel movements. Its effect on satiety is less clear, as different types of fiber can impact fullness and gastric emptying in various ways.
Step-by-step explanation:
Insoluble fiber adds bulk and can speed food's transit time through the digestive tract by promoting regular bowel movements and easing defecation. While insoluble fiber is a form of nondigestible carbohydrate that does not dissolve in water, it provides an important function by stimulating peristalsis, which is the series of wave-like muscle contractions that move food through the digestive system. The effect of insoluble fiber on satiety, or the feeling of fullness, is not as clear. Although some fibers may absorb water and swell, providing a sense of fullness, other types, such as fermentable or soluble fiber, can ultimately influence satiety differently by delaying gastric emptying.
Insoluble fiber is found in various forms, including cellulose, which are the nondigestible parts of plant walls.
Dietary fibers have varying effects on the digestive system; for instance, soluble fiber may slow the absorption of nutrients from the gastrointestinal (GI) tract, whereas insoluble fiber speeds the transit of food. Moreover, insoluble fiber sources such as lignin may influence the rate at which soluble fibers are metabolized, thereby affecting digestive health and nutrient absorption differently. Certain types of insoluble fibers like resistant starch are fermented in the colon, creating short-chain fatty acids that are beneficial for gastrointestinal health and offer protective effects against conditions such as type 2 diabetes and colon cancer.