Classification and methodology of food carbohydrates as related to nutritional effects.

Dietary guidelines encourage a considerable increase in carbohydrate intake compared with the present situation in Western countries. Recent developments regarding nutritional effects of various digestible and undigestible carbohydrates call for more detailed recommendations. The "carbohydrates by difference" concept emerged 150 y ago because of the lack of specific analytical techniques and still prevails. The concept of available compared with unavailable carbohydrate was introduced in 1929 to obtain a better measure of glucogenic carbohydrates in diabetes. Dietary fiber was first defined as the "skeletal remnants of plant cell walls," but the definition was later expanded to include all polysaccharides and lignin that are not digested in the small intestine. The gravimetric method of the Association of Official Analytical Chemists for total dietary fiber is based on this undigestibility concept. However, precipitation of soluble fiber components with alcohol, which is used in all current methods, creates an arbitrary delimitation between oligo- and polysaccharides. The complex carbohydrates concept is challenged by recent developments regarding nutritional effects of various food carbohydrates.