Why are most types of fiber indigestible in the human GI tract?

Question:

Dietary Fiber:

There are two types of fiber in the foods we eat: soluble and insoluble. Both types of fiber are beneficial to our digestive health. Soluble fiber dissolves with water in the colon and forms a gel. Foods rich in soluble fiber are oats, legumes, barley, fruits, and vegetables. Insoluble fiber passes through the digestive tract with little to no change. Wheat bran, whole grains, nuts, and seeds are good sources of insoluble fiber.

Answer and Explanation: 1