There are different forms of starch, too. These polysaccharides form what are generally referred to as complex carbohydrates. Technically speaking, a carbohydrate that contains from 3 to 6 monosaccharide units is called an oligosaccharide. These carbohydrates tend to be totally indigestible, and rather rare. Fiber is a carbohydrate consisting of many monosaccharide units.
Most fiber is derived from the cell walls of plants and is indigestible.
Polydextrose is a 12-unit polysaccharide that is similar to fiber in terms of its resistance to digestion. It is often used as a bulking agent in certain processed foods. All carbohydrates except fiber, oligosaccharides, and polydextrose are eventually converted into glucose by the body. It was once thought that simple sugars were digested and metabolized quickly, resulting in a corresponding rapid rise in blood glucose levels. It was similarly assumed that complex carbohydrates were slower to digest and, therefore, had a mitigating effect on blood glucose increases.