Probiotics means ”for life” in contrast to antibiotics which means ”against life”. WHO/FAO (2001) defines probiotics as ”live microorganisms which when administered in adequate amounts confer a health benefit on the host”. Important criteria for qualifying as a probiotic are thus that the microbes are alive and have proven health effects in clinical trials. Furthermore, a probiotic product must contain the same bacterial strain (or strains) and the same dose that was used in the clinical trials. The most common types of microbes used as probiotics are lactic acid bacteria, like Lactobacillus reuteri, and bifidobacteria.