They are referred to as complex because of the number of glucose units in their structure and the complexity of linkage. Starch is the primary storage form of glucose in plants and is easily digested by animals. Examples of high starch products are corn and potatoes. These carbohydrates are rapidly absorbed and metabolized. Fibers are the structural components of plants and also contain glucose units, but are cross-linked in various ways.
Fibers resist rapid digestion in the intestinal tract.
The main component of cereal fiber is hemicellulose. Hemicellulose is common in fruits and vegetables and is also resistant to digestion. Higher concentrations of soluble fibers are found in fruits, oats, barley and legumes. Soluble fibers generally slow the emptying of the stomach, slow glucose absorption and aid in lowering blood cholesterol. Insoluble fibers are high in vegetables, wheat and cereals.