You may have heard of probiotics, foods that contain live cultures of beneficial bacteria that live in your digestive tract and help keep it functioning well. But prebiotics are indigestible carbohydrates that nourish these good bacteria, also helping support the health of your digestive system by boosting growth of good bacterial colonies. A healthy diet rich in certain fresh fruits and vegetables is the best source of prebiotic foods.
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Dietary fiber is an indigestible carbohydrate provided by plant-based foods. One type, called soluble fiber, dissolves in water to form a gel. It's especially rich in prebiotics called fructo-oligosaccharides, which includes compounds called inulin and oligofructose. These compounds are not broken down by stomach acid or digestive enzymes but are fermented and used by beneficial bacteria in the colon, especially two types called lactobacillus and bifidobacter. Natural sources of these prebiotics include almonds, bananas, apples and vegetables such as Jerusalem artichokes, wild yams, jicama, leeks, asparagus, chicory, garlic and onions. Legumes such as soybeans are also high in prebiotics, as are whole-wheat, whole-grain oats and corn, along with made with these whole grains.
Another type of prebiotic compound is called galactooligosaccharide, or GOS. It's a natural component of human breast milk that helps get a newborn's digestive tract off to a good start by providing nutrition for the baby's colonies of beneficial intestinal bacteria. It also helps prevent pathogenic bacteria from attaching to the lining of the baby's tract. GOS is especially beneficial for bifidobacter colonies in the colon, according to a review published in the March 2007 issue of the "Journal of Nutrition," which indicates that GOS is also present in cow's milk, although at a concentration lower than in human milk.
You can increase your intake of prebiotics by adding fresh fruits and vegetables to your diet every day and by making milk part of your regular eating plan. If you have a health condition that interferes with your ability to consume fiber-rich foods or to drink milk, prebiotic supplements are also available from health-food stores, usually as tablets or capsules. Fiber supplements that contain wheat dextrin or psyllium are also good sources of prebiotics. Supplements are generally considered safe but may cause gas and bloating in some people. Discuss prebiotic supplements with your doctor or a registered dietitian to determine if they're a good choice for you.
Soluble fiber is also added during the processing of some foods, making these foods sources of prebiotics. For example, inulin is sometimes added to beverages and some baked goods and snacks, making them prebiotic foods. Another manufactured product called polydextrose that acts as a soluble fiber is also a common food additive, used to thicken and replace some sugar in cakes, candies, dessert mixes and puddings. Wheat dextrin, a grain-derived soluble fiber, is also added to soft foods and beverages by manufacturers to increase the product's thickness and to replace some dietary fat and lower calories. Check food labels to determine whether any of these soluble fiber additives are present in a particular product.