What is the difference between soluable and insoluable fiber?

Indigestible Plant. Dietary fiber, the non-digestible part of plants in our diet, consists of soluble and insoluble fibers. Soluble fiber dissolves in water and functions in the GI tract help lower blood cholesterol. Sources of soluble fiber include oats, peas, beans, apples, citrus fruits, carrots, barley and psyllium. Insoluble fiber acts to add bulk to the stool and promote regularity.