Fiber

Carbohydrate your enzymes can't digest

What does Fiber do in your body?

Plant carbohydrates that pass your small intestine undigested. Some form gels, some add bulk, and some feed gut bacteria.

How it works, step by step

  1. Fiber passes through the stomach and small intestine undigested.
  2. Soluble fiber forms a gel that slows sugar absorption.
  3. In the colon, bacteria ferment fermentable fiber.
  4. They release short-chain fatty acids that fuel colon cells.

What does Fiber do?

Adds bulk and helps material move through the gut; soluble fibers form gels that slow digestion and can lower LDL cholesterol; fermentable fibers feed colon bacteria.

Where does Fiber act in the body?

Stomach (slows emptying), small intestine (slows absorption), large intestine (fermentation).

Which foods contain Fiber?

Legumes, oats, barley, whole grains, vegetables, fruit (especially with skin), nuts and seeds.

How much Fiber do adults need?

Adequate Intake: 14 g per 1,000 kcal — about 38 g (men) and 25 g (women) aged 19–50. Daily Value on labels: 28 g.

What happens with too little Fiber?

Most people eat well below recommendations. Low intake is associated with constipation and higher heart disease risk.

Can you get too much Fiber?

Large, sudden increases cause gas and bloating; increase gradually with fluid.

What does Fiber interact with?

Very high fiber may slightly reduce absorption of some minerals.

What is known and unknown about Fiber?

Higher fiber intake is consistently associated with lower risk of heart disease, type 2 diabetes and colorectal cancer — mostly observational evidence.

Evidence & sources

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General education only, not medical advice. Drafted Oct 2026 · pending qualified expert review.