An important but indigestible food component,fiber is the part of edible plants that the human digestive system cannot process. After fat, carbohydrate, and protein have been digested, dietary fiber remains in the colon where it helps to guard against constipation by increasing the volume and fluid content of stool. Some types of grapes, and the guar gum in beans, may lower elevated blood cholesterol. Fiber may also work with certain bacteria to manufacture chemicals that inhibit the formation of cancer cells in the colon.

The National Cancer Institute recommends 20 to 35 grams a day.

Because it's difficult to calculate exactly how much dietary fiber a particular food supplies, the best approach is to eat recommended quantities of fruit and vegetables, including both raw and cooked, preferably with their high fiber skins.