What are prebiotics? How are they different from probiotics, and what health benefits do they offer?

Answers from Katherine Zeratsky, R.D., L.D.

Prebiotics are nondigestible nutrients that are used as an energy source by certain beneficial bacteria that naturally live in your intestines. Prebiotics are sometimes known as fermentable fiber.

Probiotics, in contrast, are the beneficial, or friendly, bacteria themselves. By acting as a food source, prebiotics give the probiotic bacteria a chance to exert their influence. These friendly bacteria may have several health benefits, from aiding digesting to boosting immunity. But stress, a poor diet, certain medical conditions, medications and other factors may decrease the number of healthy bacteria. Eating a diet that includes prebiotics and probiotics may help restore these friendly bacteria.

The role of prebiotics in the treatment of disease is controversial, and more studies are needed to determine their usefulness. But preliminary evidence shows that prebiotics may have a role in:

  • Improving antibiotic-associated diarrhea
  • Improving traveler's diarrhea
  • Improving gastroenteritis
  • Normalizing bowel function
  • Improving colitis
  • Reducing irritable bowel problems
  • Aiding calcium absorption
  • Boosting your immune system

Prebiotics occur naturally in a variety of foods, especially high-fiber foods, including certain fruits, vegetables and grains. The main food sources of prebiotics include:

  • Artichokes
  • Bananas
  • Barley
  • Berries
  • Chicory
  • Dairy products
  • Flax
  • Garlic
  • Greens, such as dandelion greens, chard and kale
  • Honey
  • Leeks
  • Legumes
  • Onions
  • Wheat and whole grains, such as oatmeal

Prebiotics also are added to some dietary supplements and some processed foods, such as yogurt, drink mixes and meal-replacement bars. Read food labels and claims or seek out manufacturer Web sites to help identify which products contain prebiotics. But keep in mind that not all products with naturally occurring prebiotics are labeled that way. Prebiotic supplements can be sprinkled on your food, stirred into beverages, or taken as capsules or tablets that you swallow or chew.

There's no specific guideline on how many grams of prebiotics to consume. Some studies suggest that you should get 3 to 8 grams a day to get the full benefits. In some cases, use of prebiotics may cause intestinal gas. As always, check with your doctor before taking any dietary or herbal supplements to make sure they're safe for your situation.

Oct. 24, 2009 See more Expert Answers