Probiotics, functional foods and kefir: a review of the Belgian regulation and the scientific progress in evaluating the beneficial health effects of kefir. In Belgium and more widely in Europe, conditions for putting probiotics on the market are defined on the basis of their application: medicinal or food use. Probiotics used as food supplements, as well as functional foods, are governed by food legislation. By the 31st of January 2010 at the latest, new restrictions will be introduced governing the publication of positive health claims that are authorized to be made about foods and the conditions for using them. For any other health claim, as well as for a medicinal application, the scientific evidence of the claimed effect must be provided. The potential of kefir to promote human health has been subject to various studies. These aimed to evaluate the effectiveness of probiotic strains isolated from kefir and the positive action of kefir, or some of its chemical components (fatty matter, polysaccharides), on specific health features predominantly related to cancerous tumour development, immunity, allergy and cholesteromia. The abilities of kefir to improve human health were evaluated on human cells and on laboratory animals but have not yet been confirmed by human trials.