Probiotics vs. Prebiotics: What’s the Deal?

by Leah Frankel, MS, RD

YogurtThere’s been a lot of buzz regarding prebiotics and probiotics lately.  You’ve heard rumors about yogurt and the “healthy” bacteria that yogurt contains but what’s the real deal?  Do they really work?  Do prebiotics and probiotics function differently in our body?  Do we need to be taking supplements daily?

What are probiotics and prebiotics?

There is a large debate regarding the definition of probiotics but the World Health Organization and Food and Agriculture Organization of the United Nations define probiotics as “living microorganism which, when administered in adequate amounts, confer health benefits to the host.” These microorganisms are usually bacteria and are sometimes referred to as “healthy”, “friendly”, “good” or “beneficial” bacteria. Probiotics are microorganisms similar to those that naturally exist in the gut.  The idea is that in order to stay healthy, we must maintain a delicate balance of microflora (i.e. a mix of different bacteria) in the gastrointerstinal tract.

Prebiotics are defined by several criteria: they are indigestible by the stomach and are not absorbed, they are fermented by the GI microflora (that mix of bacteria we just mentioned) and stimulate the growth and proliferation of beneficial bacteria in the gut. Prebiotics essentially help facilitate the effect of probiotics.

Where can we get probiotics and prebiotics in our diet?

Glass of MilkProbiotics (which include species of Lactobacillus, Bifidobacteria and Yeast) can be found in food as well as dietary supplements including yogurt, milk, miso, tempeh, and soy beverages. The largest group of probiotics are lactic acid bacteria (Lactobacillus acidophilus, found in yogurt, is the most well known).

Prebiotics can be derived from plants or synthesized. Sources include: soybeans, whole grains, onions, chicory root, bananas, garlic, leeks, artichokes and raw oats.

What are the proven health benefits of probiotics and prebiotics?


Studies have found multiple benefits associated with probitioics; typically probioitics are beneficial in a situation when the natural microflora in the gut may have been disturbed, as is commonly the case with antibiotic use. Probiotics have been found to:

  • Treat diarrhea

  • Treat IBS (Irritable Bowel Syndrome)

  • Prevent and treat a UTI (Urinary Tract Infection)

  • Reduce the recurrence of bladder cancer

  • Shorten the duration of intestinal infections

  • Prevent and manage eczema in children

  • Prevent and treat inflammation following colon surgery (called Pouchitis).

Prebiotics have been shown to have multiple benefits including:

  • Increased absorption of calcium and magnesium

  • Increased immune system effectiveness

  • Inhibition the growth the lesions in the gut, such as adenomas and carcinomas, therefore reducing risk factors associated with diseases in the rectum and colon.

Are there any side effects or risks associated with the use of probiotics and prebiotics?

While probiotics are generally found to be safe, few studies have been conducted on the elderly, young or immune compromised populations. In populations where probiotic use has been studied, side effects are typically mild (for example, increased gas or bloating).

GI SystemAs with probiotics, prebiotics can cause gas, bloating and increased frequency of bowel movements when consumed in large quantities (i.e. you may fart and poop more).

When prebiotics and probiotics are used together they are commonly referred to as “synbiotics”…essentially, when used together they work synergistically to provide a more beneficial probiotic effect than either would alone.

Daily consumption of foods containing these functional components is beneficial; however the effects of probiotics are dependent on the strain and species ingested and can only be assessed through clinical trials. While probiotics and prebiotics have been shown to have a variety of advantageous effects, additional supplementation is not vital since these bacteria already naturally exist in your gut and reproduce independently.

As with any supplement, always check with your doctor before beginning a new regimen. It’s important to note that dietary supplements (including vitamins and minerals) are not regulated by the FDA and therefore the product may not have the quality or purity that the label suggests. Choosing a well-known brand or looking for a USP label will ensure the product is safe.

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09 2009

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