How does fiber differ from starch in terms of digestibility?

Fiber differs from starch significantly in terms of digestibility due to its unique structural composition. The correct response highlights that fiber possesses vertical (or beta) glycosidic bonds, which the human digestive enzymes cannot break down. This structural feature makes fiber largely indigestible in the human gastrointestinal tract, allowing it to pass through the digestive system mostly intact.

In contrast, starch is composed of glucose units connected by alpha glycosidic bonds, which are readily digestible by human enzymes. This difference in bonding explains why fiber plays a crucial role in digestive health, contributing to bulk and promoting regular bowel movements, while starch serves as an important energy source for the body. Fiber’s resistance to digestion means it does not provide calories in the same way that starch does, reinforcing its classification as a beneficial component of a balanced diet.