Probiotics: mechanisms and established effects

The definition for probiotics has gradually changed with increasing underst anding of the mechanisms by which they influence human health. Health effec ts related to changes in the intestinal microflora also accompany or are re lated to adhesion and immune system effects, competitive exclusion or metab olic and nutritional effects, with an increasing array of other potential m odes of action. Most clinically documented and validated health effects hav e been studied using either fermented milks containing viable cultures or v iable pure cultures. Specific targets for the future include controlled stu dies comparing foods containing viable strains to those containing non-viab le strains and to assess the combined effects of multiple probiotics. (C) 1 999 Elsevier Science Ltd. All rights reserved.