Probiotics - What is the evidence behind the health claims?

For decades, if not longer, a host of products have been marketed as probiotics and have claimed an exhaustive range of health-promoting and disease-modifying effects. Many such claims are unsupported by evidence from high-quality human studies and many products are of doubtful provenance and quality. However, with the realization of the critical role of the 'forgotten organ', the enteric microbiota, and its interactions with the host in generating a variety of functions which sustain health and, when disrupted, lead to disease, a solid scientific basis has been developed to support the use of probiotics in infectious, allergic, inflammatory and metabolic disorders. Progress in the clinical arena has not kept pace with that in the laboratory and most health claims, be they for the prevention of illness in the healthy, or for the alleviation of an established disorder in those afflicted with a disease state, remain unsupported by incontrovertible evidence. For some conditions, however, and, most notably, diarrhoeal illnesses, some inflammatory bowel diseases, certain infectious disorders and irritable bowel syndrome, good clinical data are beginning to accumulate. Given the current changes in the regulatory attitudes towards probiotics and their health claims, it is likely that the standards for approval of a health claim will become more, and not less, stringent, thus, paving the way for high-quality clinical trials of appropriate design and duration.