Fiber

What is fiber?

Updated 4 Nov 2026

Short answer

Fiber is the part of plant food that the small intestine cannot digest. It is made of carbohydrates and lignin.[1][2] It comes from fruit, vegetables, whole grains, legumes, nuts and seeds.[1]

There are two main kinds. Soluble fiber dissolves in water and forms a gel. Insoluble fiber does not dissolve and adds bulk to stool.[1] Most high-fiber foods contain both.[3]

Supplements and fortified foods contain fibers that were taken out of plants or made in a lab, such as psyllium, inulin, polydextrose and resistant starch.[1] The US Food and Drug Administration (FDA) counts an added fiber on the label only if it has a proven health effect. Examples are lower blood cholesterol and more frequent bowel movements.[4]

Sources (4)

  1. The Role of Dietary Fiber in Health Promotion and Disease Prevention: A Practical Guide for Clinicians. Daley SF, Vadakekut ES StatPearls, 2026. PMID 32644459
  2. Scientific Opinion on Dietary Reference Values for carbohydrates and dietary fibre. European Food Safety Authority, 2010. www.efsa.europa.eu
  3. Fiber: MedlinePlus Medical Encyclopedia. MedlinePlus, US National Library of Medicine, 2026. medlineplus.gov
  4. Questions and Answers on Dietary Fiber. US Food and Drug Administration, 2024. www.fda.gov

More about fiber

How does fiber lower cholesterol?How much fiber do you need per day?What is fiber used for?How long does fiber take to lower cholesterol?Is fiber safe?Is fiber from food better than a fiber supplement?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.