What are probiotics?

According to the World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO), probiotics are "living micro-organisms that, when ingested in sufficient quantities, have positive health effects, beyond the traditional nutritional effects ". ("Report of a FAO / WHO Expert Consultation on Evaluation of Health and Nutritional Properties of Probiotics in Food Including Powder Milk with Live Lact Acid Bacteria", October 2001).