Within the definition of functional foods, there is a subset of foods believed to be good for health that are produced by or that contain live microorganisms. These foods are called probiotics.
Yoghurt, Curd, Kefir are some examples of easily available probiotics.
Yogurt is defined as a fermented milk obtained by specific lactic acid fermentation, brought about by Lb. bulgaricus and S. thermophilus. Other bacteria may be added to enhance organoleptic properties or, more recently, to increase the probiotic properties. Yogurt can now be found on the market that contains Lactobacillus, Streptococcus, Leuconostoc, and Bifidobacterium bacteria. Yogurt and yogurt-like products can be found in many countries. The amount of research on yogurt far surpasses any other probiotic product. Yogurt has been studied to determine its effects on lactase deficiency, cholesterol metabolism, immunity, infantile diarrhea, and certain cancers with varying levels of success.