Dietary fiber comprises cellulose, hemicellulose, and lignin as primary structural components of plant cell walls. Cellulose is a linear beta-1,4-linked glucose polymer providing rigidity. Hemicellulose consists of branched heteropolysaccharides including xylans and mannans. Lignin is a complex cross-linked phenolic polymer imparting hydrophobicity and strength. These macromolecules are resistant to human digestive enzymes, contributing to fecal bulk, modulating glycemic response, and supporting gut microbiota. They are insoluble in water, alcohol, and fats, exhibit high thermal stability, and decompose rather than melt or boil. Widely present in grains, vegetables, and fruits, they are essential for nutrition and food texture.