296 OLIVE OILS AND HEALTH According to the “World Gastroenterology Organisation” (WGO), prebiotics are dietary substances, mainly polysaccharides and non-starchy oligosaccharides, that nourish selected groups of intestinal microorganisms (primarily Bifidobacterium and Lactobacillus), promoting the growth of beneficial bacteria over harmful ones (Polysaccharides are complex carbohydrates composed of many simple sugars, while non-starchy oligosaccharides consist of a small number of simple sugars and do not contain starch). For a food to be considered a prebiotic, it must (1) not be digested or absorbed, (2) be selectively fermented by beneficial bacteria in the intestinal microbiota, and (3) produce health benefits. In food, prebiotics are types of plant-derived fibre that the human body cannot digest and therefore do not provide nutrients, but they serve as nourishment for the human microbiota. In this sense, not all dietary fibre qualifies as a prebiotic, only that which can be selectively used by microorganisms in the human microbiota. The best-known prebiotics include inulin, human milk oligosaccharides, and fructooligosaccharides (soluble fibre containing fructose, found in certain fruits and vegetables). Natural sources of prebiotics include vegetables (leek, artichoke, asparagus, garlic, onion, chicory, potato, etc.), cereals (wheat, oats, etc.), legumes (lentils, etc.), a variety of fruits, tomatoes, honey, nuts. Also in milk, including human milk, which supports the development of a healthy gut microbiota in newborns. In addition, prebiotics are also available on the market as dietary supplements. According to the “Food and Agriculture Organization of the United Nations” / “World Health Organization” (FAO/WHO), probiotics are live microorganisms which, when administered in adequate amounts, provide health benefits to the host. They help to maintain the intestinal microbiota in a healthy balance, especially when this balance is disrupted by external factors such as antibiotic treatments or an unhealthy diet. The most widely used species in probiotics are Lactobacillus and Bifidobacterium, although certain yeasts, enterococci, and fungi may also be used. For a microorganism to be considered a probiotic, it must: (1) be a natural resident of the gut; (2) survive the processes of production, commercialisation, distribution, and ingestion; (3) colonise the distal parts of the intestine (ileum and colon); (4) provide scientifically proven health benefits to the host; and (5) have a short replication cycle. Most probiotics are found in fermented foods, with yoghurt (produced by fermenting milk with bacteria such as Lactobacillus or Bifidobacterium) being the most common. Other fermented foods such as sauerkraut, fermented soy products, kombucha (a fermented black or green tea), and kimchi (a traditional Korean fermented food) are also good sources of probiotics. However, if these foods are filtered or subjected to high temperatures, such as during cooking or pasteurisation for food safety, their probiotic properties are lost due to the destruction of live microorganisms. Probiotics are also available on the market as dietary supplements or pharmaceutical products containing one or more microbial strains. These can be administered orally or via other routes, such as vaginally, as in the case of ovules used to treat Candida albicans (candidiasis). Additionally, live microorganisms such as Saccharomyces boulardii are commonly used to restore intestinal flora after antibiotic treatments and to help prevent diarrhoea. Although probiotics are generally considered safe, they may not be suitable for everyone. In hospitalised or immunocompromised patients, they may cause infections and should therefore only be used with caution and under medical supervision. Naturally occurring probiotics in food, such as those in yoghurt, do not carry these risks.
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