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probiotic,live microorganism administered to a host with the intention of providing a health benefit, or a food, supplement, or treatment containing such microorganisms. Many of the microbes found in the human digestive system, primarily in the large intestine, benefit human health, as by breaking down foods and making them more digestible, producing certain vitamins, and crowding out or destroying harmful microorganisms. Probiotics are intended to replenish or supply such beneficial microorganisms, but in order to be useful to the host they must be able to survive the acidic conditions of the stomach after ingestion and then establish colonies. Microorganisms regarded as probiotics are typically bacteria of the genera Lactobacillus and Bifidobacterium, but other bacteria and some yeasts also are considered probiotics.
Most studies have found that consuming or taking probiotics provides no health benefits to healthy individuals, but a number of preliminary studies have indicated that probiotics may be beneficial to some individuals with certain intestinal disorders, such as those suffering from irritable bowel syndrome or from the side effects of taking antibiotics. A report in 2017 indicated that a specific strain of Lactobacillus plantarum (one of more than 200 tested during a decade of investigation) appeared significant in preventing sepsis in babies in rural India; the bacterium had been isolated from a fecal sample from a healthy baby. How probiotics may work is not well understood, and serious complications from taking probiotics have been reported in some patients with weakened immune systems or other significant health problems.
Yogurt and other fermented dairy products; sauerkraut, kimchi, and other fermented vegetable preparations; and other foods produced by the action of live bacteria are typically regarded as, and marketed as, probiotic. Some foods are sold fortified with probiotic microorganisms, and capsules and pills containing freeze-dried probiotic microorganisms are sold as probiotic supplements. These foods and supplements, however, contain usually several varying strains and amounts of microorganisms, are not subject to regulatory controls, and have not been approved by U.S. or European Union agencies for treatment of any health problem. The freshness of yogurt and other probiotic foods also is a factor in their value as a potential source of live probiotic microorganisms.