You should try to eat at least 25 to 30 g of fiber a day. Fiber is a complex carbohydrate found only in plant foods, primarily whole grains, legumes, fruits, and vegetables. Because fiber is resistant to digestive enzymes, it passes through the digestive tract without being absorbed and is eliminated in stool.
Fiber comes in two forms: soluble, the type in oatmeal that gets sticky when wet; and insoluble, the sponge-like version in bran and fruit and vegetable skins that absorbs water. Both types of fiber are important, but soluble fiber is especially effective in lowering blood cholesterol levels. Just how soluble fiber reduces cholesterol levels is unclear. But researchers theorize that soluble fiber interferes with the intestinal reabsorption of substances called bile acids, which are produced from cholesterol in the liver. Bile acids that are not reabsorbed are eliminated from the body in stool. As a result, the liver ends up converting more cholesterol into bile acids.
It’s best to get your fiber from foods, because they contain a variety of other nutrients. Good sources of soluble fiber include oats, oat bran, barley, legumes, dried plums (prunes), apples, carrots, and grapefruit. Whole grains( like whole wheat, barley, brown rice, and quinoa), seeds, and most vegetables are rich in insoluble fiber. For people who find it difficult to get enough fiber in their diet, regular use of products that contain fiber from psyllium seeds—such as Metamucil—can lower cholesterol levels by 5 to 10%.