Fiber and Lactose

Fiber and lactose are two common food substances that can cause problems with diarrhea.

Fiber comes from the portion of plants that is not digested and, therefore, passes intact through the digestive tract. There are two classes of fiber: fiber that dissolves in water (soluble) and fiber that does not (insoluble). Insoluble fiber can increase the rate of food passing through the digestive tract, whereas soluble fiber can decrease the rate.

If your intestinal tract is irritated, the normal amount of insoluble fiber may be too much. Minimizing your intake of insoluble fiber may help relieve diarrhea.

Insoluble Fiber

To reduce the amount of insoluble fiber in your diet, avoid the following foods:

  • Nuts
  • Seeds
  • Wheat bran
  • Whole grains
  • Dried fruits

Instead of the foods above, try to eat the following:

  • Tender cooked vegetables — Examples include canned or cooked tender asparagus, beets, carrots, pumpkin or squash.
  • Canned or cooked fruits — Examples include canned applesauce, apricots, peaches and pears. Ripe bananas and citrus fruits without seed and membranes also are fine.
  • Refined starches — Examples include refined, cooked or dry commercially prepared corn, oat, rice or wheat cereals, enriched white, refined wheat or light rye bread, noodles from refined flour, rice without the hull and potatoes without skin.

Soluble Fiber

To increase the amount of soluble fiber in your diet, try eating:

  • Oatmeal
  • Applesauce
  • Bananas
  • Potatoes


Reviewed by health care specialists at UCSF Medical Center.

This information is for educational purposes only and is not intended to replace the advice of your doctor or health care provider. We encourage you to discuss with your doctor any questions or concerns you may have.

Related Information

UCSF Clinics & Centers


Gastroenterology at Mount Zion
1701 Divisadero St., Suite 120
San Francisco, CA 94115
Phone: (415) 502-4444
Fax: (415) 502-2249

Gastroenterology at Parnassus
350 Parnassus Ave., Suite 410
San Francisco, CA 94143
Phone: (415) 502-2112
Fax: (415) 514-3300

Colitis and Crohn's Disease Center
1701 Divisadero St., Suite 120
San Francisco, CA 94115
Phone: (415) 353-7921
Fax: (415) 502-2249

Condition Information