Mysterious Pre- and Probiotics

Prebiotic and probiotic, two words often used to market food and supplement products to the general public.

As a Registered Dietitian, I’ve had many people tell me that they don’t truly understand exactly what they are, what they do, and why they are, in most cases, beneficial for our health.


Mission: Unfold the mystery of Gut Flora

If you accept this mission, you will have a deeper understanding of why it is beneficial for you to include wonderful healthy bacteria in your daily eating plan.

Disclaimer: This blog is not recommending that everyone should purchase and/or use prebiotic and probiotic supplements. This discussion will focus on pre- and probiotic food sources but will also provide some basic supplement education information to be used for discussion with your healthcare provider about, specifically, whether or not probiotic supplements will benefit you.

Healthy bacteria live throughout the body, actually 90% of our cells are microbes a.k.a. bacteria. Specifically, the healthy bacteria found in the small and large intestines, a.k.a. gastrointestinal (GI) tract, are known as gut microbiota, intestinal flora, gut flora, and a few other names. This blog will specifically discuss gut flora from this point forward.

Incredibly, The Gut Microbiota For Health website explains that our gut flora is such a vital part of the body that “experts nowadays consider it as an organ.” It also discusses that approximately two thirds of our gut flora are specifically created for our individual bodies. This means that the same bacteria may not be found in someone else’s gut! In essence, our body has its own private blend of gut flora based upon each body’s individual needs. Now that’s cool!

The American Nutrition Association reports that our gut flora is made up of approximately one hundred trillion bacteria of which, 85% is healthy and 15% is unhealthy. There are roughly 500 different species but the healthy bacteria are predominantly made up of around 30-40 of the species.

Prebiotics, Probiotics, and Synbiotics

Probiotics: living microorganisms (bacteria) and sometimes yeasts found in foods, dietary supplements, medical foods, and some drugs, in countries other than the U.S., operative word is living. Once ingested, probiotics add to the valuable gut flora in the body and have been scientifically proven to be beneficial for your health, e.g. lactobacillus

Prebiotics: essentially indigestible carbohydrates that feed the gut flora (healthy bacteria) found in the GI tract, e.g. artichoke

Synbiotics: food and/or supplement products that contain both pre- and probiotics that work together, e.g. Kefir

It's All In the Name

Per the California Dairy Research Foundation, probiotic names are made up of a genus (bacteria), species, and strain. “For example, Lactobacillus (genus), rhamnosus (species), and GG (strain).”

Some of the more common natural probiotic names you’ll see listed in food and/or supplements are Lactobacillus, Bifidobacterium, Streptococcus, Escherichia, Enterococcus, Bacillus, and Saccharomyces (yeast).  

Proven Pre- & Probiotic/Yeast Use for Some Conditions

Different bacteria perform different functions in the body. As seen in the list below, when choosing foods and/or products, it is beneficial to know what strains have been studied and shown to be effective for specific conditions and/or overall general health.

  • Inflammatory Bowel Disease (IBD) E. coli Nissle, Lactobacillus, Bifidobacterium, Streptococcus
  • Irritable Bowel Syndrome (IBS) Bifidobacterium infantis, Sacchromyces boulardii, Lactobacillus pantarum, Lactobacillus acidophilus and Bifidobacterium
  • Infectious DiarrheaLactobacillus rhamnosus, Lactobacillus casei, many Lactobacillus strains, and the yeast Saccharomyces boulardii
  • AAD (antibiotic-associated diarrhea)- Lactobacillus acidophilus and rhamnosus, Saccharomyces boulardii (yeast)
  • Traveler’s Diarrhea - Saccharomyces boulardii
  • Lowering presence of unhealthy gut bacteria overallLactobacillus, Lactobacillus acidophilus
  • Immunity Building - Bifidobacterium lactis
  • Constipation management - yogurt with lactobacilli and bifidobacteria
  • Ulcerative colitis - inulin and oligofructose (prebiotics)
  • Improved lactose intolerance symptoms - Lactobacilli and bifidobacteria combined with prebiotics

The Need For Pre- and Probiotics

If the 85/15% Healthy/Unhealthy bacteria gut flora balance is not maintained, the imbalance can interfere with many of the vital gut flora functions listed below:

Gut Flora Vital Functions :

  • Producing vitamins B and K that support skin, nervous system, blood, bone, and cardiac health
  • Maintaining immunity by creating antibodies and stopping unhealthy bacteria from growing
  • Maintaining proper digestion
  • Maintaining overall GI tract health, which includes the colon and bowel function
  • Maintaining overall skin health
  • Increases lactose tolerance
  • Preventing dental caries (cavities)
  • Breaking down and destroying toxins in the body
  • Possible positive impact on brain function (being studied)
  • Possible positive impact on conditions such as asthma and eczema (being studied)
  • Possibly decreasing the risk of some cancers e.g. colon
  • Possibly decreasing kidney stones caused by elevated urine oxalate (being studied)
  • Maintains healthy vaginal microbiota
  • Inhibits the growth of helicobacter pylori
  • Improves calcium absorption

What Upsets the Gut Flora Balance?

  • Antibiotics – anti means “against” and biotics means “from living organisms”, so antibiotics destroy much of the good and the bad bacteria leaving the body in need of replenishing the healthy flora
  • NSAIDs (non-steroidal anti-inflammatory medication) – e.g. ibuprofen and naproxen
  • GI infections – e.g. food poisoning, e-coli
  • GI surgeries, chemo/radiation therapy
  • Colonoscopies – procedure and preparation
  • Unhealthy diet
  • Pollutants – e.g. heavy metals
  • Some over-the-counter drugs – e.g. aspirin, antacids,
  • Possibly some prescription drugs – antidepressants, sleeping pills, SSRIs (selective serotonin reuptake inhibitors)
  • Some also suspect: pesticides, herbicides, artificial food coloring, and antibacterial products

Improving and/or Replenishing the Gut Flora

We have to rely on CFUs, the acronym for “colony forming units”, which refers to colonization a.k.a. taking up residence and living in the host. In this case the host is the gut.

Remember earlier where I said the operative word in the probiotics definition is live? Well, that’s because microbial colonies cannot be formed if the ingested probiotics are dead, so this is how the live bacteria counts of probiotic products are measured. The live and active cultures found in foods such as yogurt aid in recolonization of the normal gut flora destroyed by things such as antibiotics.

CFU ability is also why, when purchasing probiotic products such as foods or supplements, you should always look for labels about the bacteria. For example, the National Yogurt Association has the LAC (Live & Active Cultures) seal that can only be on products that have volunteered for the program and proven that their product contains at least 100 million bacteria per gram of product.

For an additional example, on the Lifeway website for their Kefir product, it reports that Kefir contains 15 – 20 billion CFUs of live and active cultures per one cup serving. It also lists the strain names and some other specific information about CFUs in other Lifeway products. Link to information:

You will also see some products may not have the LAC seal but may say “contains live cultures”, “contains active cultures”, “contains live and active cultures”, or have the live specific strains listed in the ingredients, e.g. lactobacillus.

Just because a product has yogurt in the name does not indicate that it contains live and active cultures. That’s because if the yogurt was heated afterwards, the bacteria would die. For example, most yogurt covered pretzels do not have live and active cultures, unless specifically labeled that they do.  

Maintaining the life of the probiotics in food and/or supplements is also why it is important to read the instructions for how to store the items. For example, we all know we have to refrigerate our yogurt that contains live and active cultures but there are also many probiotic foods/supplements that, once opened, have to be refrigerated or else the bacteria die.

Foods Naturally Containing Pre- and/or Probiotics 

Probiotic Foods:

  • Yogurt labeled as having “Live and Active Cultures” or listing specific probiotic strains in the ingredients list.
  • Kefir products
  • Other Cultured Dairy Products –buttermilk, chaas, bonny clabber (Scottish), filmjölk (Swedish), viili (Scandinavian), piimä (Scandinavian), matsoni (Eastern European), blaand (Scottish)
  • Aged Cheese - that contain active live cultures
  • Kimchi
  • Sauerkraut
  • Miso
  • Tempeh
  • Sour pickles
  • Many foods, snacks, drinks, smoothies, etc. have pre- and/or probiotics added to them, simply verify that they are labeled properly with live and active cultures

Prebiotic Foods:

  • Bananas
  • Green, raw bananas and plantains
  • Chicory root, raw
  • Honey
  • Acacia gum
  • Leeks
  • Onions
  • Garlic
  • Asparagus
  • Artichokes
  • Soybeans
  • Whole grains, such as whole wheat
  • Legumes
  • Unpasteurized apple cider vinegar
  • Dandelion greens and root
  • Cooked and cooled potatoes
  • Cooked and cooled rice
  • Marine algae
  • Brewer’s yeast
  • Specific mushrooms – shiitake, reishi, maitake

Prebiotic Food Product Additives (freeze-dried and added to foods and/or supplements)

  • FOS – fructo-oligosaccharides
  • Inulin – partially indigestible starch found in onion, garlic, and other foods

Are Probiotic Supplements Safe?

Buyer beware! It is important to use reputable brands that focus on providing a quality pre- and probiotic product. Remember that in the U.S., the FDA regulates the marketing and health claims of our products but that does not always indicate the quality.

Many people are purchasing products online from other countries and might not know how and if the products are regulated. It is very scary to note that many products claiming specific amounts of live probiotic strains, CFUs, etc., have, been randomly tested, and not really provided what was stated as well as using things that may not be beneficial at all.

In the U.S. there is the USP Verified Mark seal, which stands for U.S. Pharmacopeial Convention and indicates that the supplements have met specific stringent requirements for quality and safety. It looks like the picture below and here is a link for more information


Should Everyone Use Probiotic Supplements?

Generally speaking, probiotics are safe for most healthy people but there are some groups that they may not be appropriate for, such as people on certain medications because they may interfere with the effectiveness, some products must be avoided by those with milk allergy, and, if you’re going to give them to children, verify with your pediatrician that they approve of using them and that there is not contraindication.  

Additionally, pre- and probiotic supplements should only be recommended and used under medical supervision for those that are immunocompromised, recovering from surgery, have a compromised gastrointestinal system, other illnesses, and/or are at a greater risk of infection, overall. This is for both adults and children.

Keep in mind that if something like an antibiotic is being used and depleting the healthy gut flora, consuming probiotic food sources and/or a supplement throughout the antibiotic course and, for some time after finishing the antibiotics, may be necessary to fully replenish the normal amount of healthy gut flora.

This is an opportune time to have a discussion with your health care provider, whether it’s your M.D., R.N., R.D., or Pharmacist because, hopefully, they can give you specifics about how much to take, what strains are the best, the best timing for when to take it in order to not interfere with the medications effectiveness, and how long to continue the probiotic course after the antibiotics have stopped.  

Are There Any Side Effects from Probiotic Supplements?

Some people complain of gas and bloating but, it is not usually severe and goes away once the body acclimates to the pre- and/or probiotic.

There are some that find that they are allergic to the product or cannot tolerate certain types or strains. For example, due to certain GI conditions I have, I am intolerant of most prebiotic foods/supplements, especially chicory root, inulin, and FOS (fructooligosaccharides) in any foods and/or products I consume.  

Hopefully the mystery has been somewhat unraveled but, as you can see from the length of this blog, there is so much more to learn about this subject. Perhaps you’ll find some of the resources below helpful in discovering even more.


California Dairy Research Foundation

TED (Technology, Entertainment and Design) Talk “Rob Knight: How our microbes make us who we are”

The New York Academy of Sciences free “More than a Yogurt Cup” podcast

Today’s Dietitian article that reviews some over the counter probiotic supplements:

National Yogurt Association: Live and active culture FAQ’s