What are Probiotics?
Probiotics are “live microorganisms, which, when administered in adequate amounts, confer a health benefit on the host. ” (Microorganisms are tiny living organisms — such as bacteria and yeasts — that can be seen only under a microscope.) Although bacteria and other microorganisms as often thought of as harmful “germs,” many “good microorganisms” help our bodies function properly. Bacteria that are normally present in our intestines helps us to better digest food, make vitamins, and destroy disease-causing microorganisms, for example. Our bodies contain a large number of microorganisms. In fact, they are reported to outnumber human cells by a factor of 10 to 1. Many of the microorganisms in probiotic products are the same as or similar to microorganisms that naturally live in and on our bodies.
Probiotics are available in foods and dietary supplements (including pills and powders). Some probiotic foods date back to ancient times, such as fermented foods and cultured milk products. Other common foods containing probiotics include yogurt and some juices and soy beverages. Some probiotics are also available topically (such as in skin creams).
Most probiotics are bacteria similar to those naturally found in people’s guts, especially in those of breastfed infants. These bacteria provide natural protection against many diseases. Common types of probiotic microorganisms include bacteria from two groups, Lactobacillus or Bifidobacterium. Within each group, there are different species (Lactobacillus acidophilus and Bifidobacterium bifidus, for example), and within each species, different strains (or varieties). A few common probiotics, such as Saccharomyces boulardii, are yeasts, which are different from bacteria.
 World Health Organization and the Food and Agriculture Organization of the United Nations