Effects of prebiotics on mineral metabolism.

Nondigestible oligosaccharides (NDOs) have been found to stimulate absorption of several minerals and to improve mineralization of bone. Hence, these substances are potential ingredients for "functional foods." In addition to a nutritional effect, functional foods have physiologic and psychological benefits that result in improved health or reduced risk of chronic disease. Most of the scientific evidence for the functional effects of NDOs is based on animal experiments in which NDOs increased the availability of calcium, magnesium, zinc, and iron. This stimulatory effect of some NDOs is assumed to be mainly due to their prebiotic character. A prebiotic is defined as a substrate or food ingredient that is nondigestible for the host but is fermented selectively by some of the intestinal microflora. Thus, it stimulates the growth and activity of bacteria with beneficial consequences for the host's health. Recently, these findings were confirmed in human studies for some NDOs. The effects seem to be specific for the type of carbohydrate and are likely related to the rate of fermentation by the intestinal flora and appear to depend on the ingested dose. Contradictory results of the effect of prebiotics in literature may be due to the experimental design because the effect of NDOs depends on the dose, the time of administration, the content of calcium in the diet, the part of the skeleton investigated, and the age of the subjects studied.