Everything you need to know about pre & probiotics

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This is a guest post from Susan Macfarlane, a Registered Dietitian Nutritionist utilizing Cronometer to help run a busy private practice in Ontario, Canada.

In the ongoing pursuit of health, wellness, and longevity, scientists and health professionals have turned their attention inward, specifically towards our guts. It’s estimated that our gastrointestinal (GI) tract contains approximately 100 trillion bacteria, with two thirds of these being unique to each individual (1). In addition, the 1000+ different species of bacteria living in our GI tract contain 3 million plus genes; 150 times more than the human genome (2)!

In light of this, scientists are starting to explore the role that our gut microbiota plays in the prevention of disease and achievement of health. Specifically, scientists wonder if dietary changes and supplementation with pre and/or probiotics can favourably alter a person’s gut microbiota to achieve health benefits and aid in the treatment of disease. In this post, we’re turning to the science to determine what role prebiotics and probiotics play in human health.



According to the International Scientific Association for Probiotics and Prebiotics, prebiotics are “selectively fermented ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health” (1). Simply put, prebiotics are the food that good bacteria (living on or in us) feed on, resulting in a positive health outcome.

Many people tend to use the terms “prebiotics” and “dietary fibre” interchangeably; while a large majority of prebiotics are classified as dietary fibre, not all sources of dietary fibre are prebiotics (3). The following list is the most common types of prebiotics, along with their source: (3):

β (beta)-Glucan    
Sources: Cereal grains (oat and barley), mushrooms (reishi, shitake, maitake), algae, seaweed.

• Galactooligosaccharides
Sources: Agave, bananas, onions, chicory root, garlic, asparagus, jimica, leeks, wheat, barley, Jerusalem artichoke.

• Isomaltooligosaccharides
Sources: Honey, miso, sake, soy sauce – also used as an ingredient by the food industry.

• Guar Gum
Sources: Made from the endosperm of the plant Cyamopsis tetragonolobusUsed as an ingredient in baking, cereals, dairy, and meat products.

• Lactulose
Sources: Made from lactose; not found naturally in foods.

• Resistant Starches & Maltodextrin
Sources: Bananas, potatoes, grains, pulses, seeds.

• Xylooligosaccharides & Arabinooligosaccharides
Sources: Not found naturally in foods


Health Benefits of Prebiotics

The greatest benefit of prebiotics is their ability to promote the growth of good bacteria in the GI tract. In addition, prebiotics that are fermented (or broken down) in the intestinal tract produce the short-chain fatty acids – butyrate, acetate, and propionate – which are responsible for regular bowel movements, a possible decrease in cancer risk, and the promotion of a healthier GI barrier that works to keep pathogens known to cause inflammation and disease at bay (4).



The definition of probiotics used by the International Scientific Association for Probiotics and Prebiotics is “living microorganisms that confer a health benefit on the host when administered in adequate amounts” (1). However, there are no legal definitions or enforced standards for probiotics sold by companies.


Strains of Probiotics

Although probiotics may be found in some foods (such as dairy and plant-based alternatives), the most common source of probiotics are supplements. When it comes to evaluating the efficacy of a probiotic, it’s important to consider the health condition under which the strain of probiotic has been studied, along with the dose that has been demonstrated to be effective, as these two factors will determine whether the probiotic could confer any benefit. Additional information to look for on the probiotic label to ensure it is high quality includes (1):

  • Name of the probiotic strain (ensure that it agrees with scientific nomenclature)
  • A count of living bacteria at the end of shelf-life
  • Recommended storage conditions
  • Safety information
  • Description of how the probiotic works in the body
  • Contact information of the company

The following covers health conditions shown to benefit from probiotic use, the associated strains/prebiotic, and the recommended dose. (Note that this information applies to adults only; 1):

Prevention of antibiotic associated diarrhea

  • Eterococcus faecium LAB SF68
    •  Recommended Dose: 108 cfu – 2x per day
  • Saccharomyces boulardii strain of Sarcharomyces cerevisiae
    • Recommended Dose: 4 x109 cfu – 4x per day

  • Lactobacillus acidophilus CL 1285 + lactobacillus casei LBC80R
    • Recommended Dose: 5 x 1010 cfu – 1-2 x per day

Irritable Bowel Syndrome 

  • Bifidobacterium infantis 35624
    • 108 cfu – 1x per day

  • Bifidobacterium animalis DN-173010 in fermented milk
    • 1010 cfu – 2x per day

  • Lactobacillus acidophilus SDC 2012, 2013
    • 1010 cfu per day


Treatment of Constipation

  • Lactulose
    • 20-40 g per day
  • Oliofructose
    • >20 g per day


Prevention of common infections in athletes

  • Lactobacillus casei Shirota in fermented milk
    • 1010 cfu – 1x per day


Health Benefits of Probiotics

As mentioned, the health benefit of probiotics is dependent upon the health condition under study, the strain of probiotic, and the dose applied. Currently, the best evidence shows that probiotics are effective at improving immunity and the overall healthfulness of the GI tract (1). In addition, evidence exists for the role of probiotics in the treatment and management of diarrhea (acute, traveler’s, and antibiotic-related), the eradication of H. pylori (along with conventional treatment), liver disease, atopic dermatitis, irritable bowel syndrome, ulcerative colitis, and potentially, colon cancer (1).


Who Should Take a Probiotic?

Although the side effects of using probiotics appears minimal, there is a lack of long-term safety data on the use of probiotics and serious side effects are possible in individuals with weakened immune systems. As such, it’s important to speak with your doctor before starting a probiotic supplement.  

Healthy individuals with diarrhea, irritable bowel syndrome, ulcerative colitis, constipation, H. pylori, or any of the other conditions listed in the World Gastroenterology Organization’s Global Guideline on Prebiotics and Probiotics may benefit from the addition of a probiotic (1). For healthy individuals without such conditions, the benefit of a probiotic likely outweighs any potential side effect, but for many, the cost of probiotics will prohibit their use. Thankfully, for these individuals, simple dietary changes can help to promote healthy gut flora (5):

  • Get enough dietary fibre (track this in your Cronometer account!)
  • Include plenty of plant-based foods (vegetables, fruit, whole and unprocessed grains, pulses, nuts and seeds) which are rich in antioxidants and polyphenols that reduce gut inflammation
  • Include fermented foods like coconut yogurt/kefir, sauerkraut, miso, and tempeh
  • Avoid artificial sweeteners
  • Limit processed foods



  1. Guarner F, Sanders ME, Eliakim R, Fedorak R, Gangl A, Garisch J, et al. Prebiotics and probiotics. World Gastroenterology Organization Global Guidelines. 2017 Feb. Available here.
  2. European Society for Neurogastroenterology & Motility (ESNM). Gut microbiota info. n.d. Available here.
  3. Carlson JL, Erickson JM, Lloyd BB, Slavin JL. Health Effects and Sources of Prebiotic Dietary Fiber. Curr Dev Nutr. 2018 Jan 29; 2(3):nzy005. Available here.
  4. Coleman Collins S. Entering the World of Prebiotics — Are They a Precursor to Good Gut Health? Today’s Dietitian. 2014 Dec. 16(12):12. Available here.
  5. National Center for Complementary and Integrative Health (NCCIH). Probiotics: In Depth. 2016 Oct. Available here.

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