Q: We hear a lot about probiotics, but recently I heard another term: "prebiotics." What are these?
A: That term refers to food ingredients that nourish probiotics. Typically, they are fibers and certain sugars that we don’t digest or absorb but that the bacteria in our intestines feed on, thereby stimulating their growth and activity. Examples are fructooligosaccharides (FOS), galactooligosaccharides (GOS), lactulose, and inulin (a fiber-like substance).
Prebiotics occur naturally in small amounts in many carbohydrate-rich foods, including whole grains, legumes, fruits, and vegetables. They are increasingly being added to foods, too—from yogurts and cereals to juices and even chocolate—and are also available as dietary supplements.
Like probiotics, prebiotics alter the balance of different bacteria in the intestines. Many proposed health benefits, such as for certain bowel problems, are thus similar to those made for probiotics—though most of the research on prebiotics has been in animals and test tubes. Some studies in people have shown that prebiotics enhance calcium and magnesium absorption, which might help keep bones strong.
Bottom line: Prebiotics are considered safe, so it’s okay to eat them in yogurt and other healthful fortified foods. At the very least, yogurt with added inulin provides some fiber and may boost calcium absorption somewhat. But as with probiotics, it’s not clear which kinds may be best for which conditions or what the optimal dose would be. And large amounts may cause abdominal pain, flatulence, bloating, and even diarrhea. Oatmeal, barley, onions, bananas, asparagus, leeks, and artichokes are just a few natural sources. We don’t recommend prebiotic supplements.
Also see Probiotics Pros and Cons.