Which of the following is insoluble fiber?

• A. Soluble fiber
• B. Psyllium
• C. Oat bran
• D. Wheat Bran

Answer: (D)

Insoluble fiber does not dissolve in water and mainly adds bulk to stool, speeding up intestinal transit. Wheat bran fits this profile, being high in insoluble fibers like cellulose and other insoluble polysaccharides that remain intact in water and increase stool mass. Psyllium and oat bran are dominated by soluble fibers—psyllium forms a gel, and oat bran contains beta-glucans that dissolve in water and have gel-like properties. So, among these options, wheat bran is the insoluble fiber.