Don't wait until you've had a heart attack to start boosting your fiber intake! Dietary fiber is the term for several materials that make up the parts of plants your body can't digest. Fiber is classified as soluble (can be dissolved in water) or insoluble. Good sources of soluble fiber include oats, beans, peas, rice bran, barley, citrus fruits, strawberries and apples. Foods high in insoluble fiber include whole-wheat breads, wheat cereals, wheat bran, rye, rice, barley, most other grains, cabbage, beets, carrots, Brussels sprouts, turnips, cauliflower and apple skin.