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Soluble vs. insoluble fiber

There are two different types of fiber -- soluble and insoluble. Both are important for health, digestion, and preventing diseases.

  • Soluble fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. It is also found in psyllium, a common fiber supplement. Research has shown that soluble fiber helps lower cholesterol, which may help prevent heart disease.
  • Insoluble fiber is found in foods such as wheat bran, vegetables, and whole grains. It adds bulk to the stool and appears to help food pass more quickly through the stomach and intestines.

Alternative Names

Insoluble vs. soluble fiber; Fiber - soluble vs. insoluble

Images

References

Hensrud DD. Diet and nutrition. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 13.

Iturrino JC, Lembo AJ. Constipation. In: Chung RT, Rubin DT, Wilcox, CM, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 12th ed. Philadelphia, PA: Elsevier; 2026:chap 20.

Saint-Cyr M, Waldrop SW, Krebs NF. Nutritional requirements. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 60.

Review Date 8/25/2026

Updated by: Angela K. Pham, MD, Department of Gastroenterology, Hepatology, and Nutrition, University of Florida, Gainesville, FL. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. Editorial update 09/15/2026.