Probiotics: established effects and open questions.

Human intestinal microflora is a complex ecosystem with hundreds of bacterial species. Its metabolic functions and interactions with the host probably affect the human health and well being, but these effects are extremely difficult to study. However, for about 100 years, the idea of modifying the composition of colonic flora by consuming viable bacteria in order to improve the quality of life and to prevent and treat intestinal disorders has had some popularity. Solid clinical data have usually been lacking to support the health claims associated with these so-called probiotics. The situation, however, is rapidly changing. Competent clinical studies are accumulating, showing that specific probiotic microbes, mainly lactic acid bacteria and bifidobacteria, can alleviate or prevent diverse intestinal disorders and reduce the risk of some intestinal diseases. Some indication of the mechanisms of action can also be deduced from the data available, while rapidly developing molecular biological methods offer new tools to verify the survival of the probiotics in the gut and the subsequent adhesion to mucosae. While development of foods containing probiotic bacteria has a great potential for the food industry and can be expected to positively affect the general health of the population, safety considerations have to be taken into account while introducing new species or strains without a previous history of safe food use.