The term ‘probiotic’ is derived from the Greek pro (for) and bios (life) meaning ‘for life’. The concept of supplementing diet with probiotics evolved at the turn of the 20th century from a hypothesis proposed by Nobel Prize-winning Russian scientist Eli Metchnikoff. Metchnikoff suggested that the long, healthy life of Bulgarian peasants resulted from their consumption of fermented milk products and that the fermented lactobacillus positively influenced the microflora of the colon by decreasing toxic microbial activity. Over the past decade research in probiotic health benefits has exploded, discovering new bacteria and their effect at an unprecedented speed. The beneficial effects of probiotics likely result from several complex, interacting mechanisms that will differ for different strains and sites of activity.