Most plant-based foods, such as oatmeal and beans, contain both soluble and insoluble fiber. However, the amount of each type varies in different plant foods. To receive the greatest health benefit, eat a wide variety of high-fiber foods. This type of fiber dissolves in water to form a gel-like material. 2  It can help lower blood cholesterol and glucose levels. 3  Soluble fiber is found in oats, peas, beans, apples, citrus fruits, carrots, barley and psyllium. 4  Insoluble fiber.