What specific action does insoluble fiber provide regarding stool consistency and movement?

It adds bulk to stool, helping material move through the digestive tract more quickly.

Dietary fiber is categorized into two main types based on its interaction with water, and insoluble fiber performs a distinct mechanical function within the colon. Unlike soluble fiber, insoluble fiber does not dissolve into a gel-like consistency when mixed with water. Instead, its primary role is structural; it remains relatively intact as it travels through the gastrointestinal tract. By remaining coarse and undigested, this type of fiber significantly increases the overall bulk or volume of the fecal matter. This increased bulk provides necessary substance that stimulates the intestinal walls, promoting regular peristalsis (muscle contractions) and thereby ensuring that waste material moves more rapidly and efficiently through the lower digestive system.