The primary function of dietary fiber is to promote digestive health. It adds bulk to stool and facilitates its passage through the intestines, preventing constipation. Additionally, fiber supports a healthy gut microbiota by serving as a substrate for fermentation, which produces beneficial short-chain fatty acids. These actions help maintain bowel regularity and reduce the risk of colorectal diseases. Unlike macronutrients, fiber is not digested for energy and does not participate in protein synthesis or hormone production.

Reference: Guyton and Hall Textbook of Medical Physiology, Guyton AC, Hall JE, 14th Edition.