Consider the fundamental change from milk to brie cheese or grapes to wine. Such is the power of fermentation. Fermented foods result from the growth and metabolism of live cultures, transforming a precursor food (such as milk) into a fermented food (cheese). The fermentation process may result in changes in taste, texture, aroma, nutritional value, microbial content and perhaps health benefits that extend beyond the basic nutritional value of the food. Because of this last property, some call fermented foods ‘probiotics’, but in fact they are not (necessarily) the same.
Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host (Hill et al. 2014). Unlike fermented foods, probiotics must have been tested in human studies and shown to have a beneficial health effect. Fermented foods don’t require such testing, although some have been. Further, some fermented foods are treated after they are made (for example, sourdough bread is baked), and do not contain live microbes at the point of consumption. To the extent a fermented food has been tested in human studies and shown to be beneficial and delivers a sufficient ‘dose’ of beneficial live microbes, it meets the bar of a probiotic. (See figure below). This is the case with several probiotic yogurts and fermented milks on the market today.
You likely have seen publicity and testimonials about how good for you fermented foods such as kombucha or sauerkraut are. But this is not the same as evidence from controlled, human studies. Many of these foods may be good for your gut or immune system, but in the absence of studies, we can’t confidently say. If you enjoy them and they make you feel better, they are great additions to your diet. Scientists are now speculating that any source of live microbes may turn out to be beneficial and are even suggesting addition of an RDA for live microbes as part of a healthy diet.
For a comprehensive dive into the science of probiotics and human health, head to this review.
The body of evidence substantiating benefits of probiotics is quite extensive. Over 1800 human trials have been conducted using probiotics. See table below for a list of some benefits of probiotics shown in human trials. Keep in mind that benefits are tied to specific strains. It’s easy to grasp this concept if you look to the animal world. Different breeds of horses, for example, have quite different strengths and functions. You wouldn’t ride a pony in the Kentucky Derby, even though both Secretariat and a pony are the same species. Similarly, different strains of even the same species of a probiotic may have different benefits. In some cases, more than one independently tested probiotic product confers the same benefit. In other cases, only a single probiotic product has been shown to be effective. The best evidence for probiotic use is for prevention of antibiotic-associated diarrhea and C. difficile infection, management of certain gut symptoms, and prevention of necrotizing enterocolitis in preterm infants. People often wonder if probiotics have any benefit for healthy people. Benefits such as improved tolerance of dietary lactose for lactose intolerant people, management of blood lipids, improved oral health, reduced incidence of common infectious diseases such as the common cold, and management of gut symptoms all are demonstrated in reasonably healthy people.
The probiotic marketplace can be confusing for consumers. See here for some basic information on choosing a probiotic and reading a probiotic label. Some basic principles to guide your search:
- There is no one strain or one dose that is best. Sometimes lower dose products or products with fewer strains have the best evidence.
- Any health benefit claim made should be substantiated with a human trial. But the types of claims allowed in the USA on foods and dietary supplements are restricted by law. Contact the manufacturer to get information on what studies have been conducted, or consult Clinical Guide for Probiotic Products Available in the United States.
- One of the biggest challenges in the probiotic market is keeping the probiotic strain alive. Responsible manufactures go to great lengths to be sure their probiotics retain viability and deliver an efficacious dose through the end of the product’s shelf life. Unfortunately, not all products on the market are responsibly formulated. Consumers should buy products from companies they trust.
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For product manufacturers interested in offering consumers fermented foods, adding research-supported probiotics can ensure consumers are getting the health benefits they expect from fermented foods.
Overview of some benefits of probiotics in humans as established in randomized, clinical trials. Consult individual references cited for strains and doses. Adapted from Sanders, Merenstein, Merrifield and Hutkins, Nutrition Bulletin.
| Benefit | Population | Reference |
| Treat colic in breastfed infants | Infants | Sung et al. 2018 |
| Prevent atopic dermatitis/food hypersensitivity | Infants | Zhang et al. 2016 |
| Prevent necrotizing enterocolitis | Premature infants | AlFaleh & Anabrees 2014 |
| Treat acute diarrhea | Infants, children | Szajewska et al. 2013 |
| Manage symptoms of occasional constipation | Adults | Eskesen et al. 2015 |
| Manage symptoms of lactose intolerance | Children, adults | EFSA Panel on Dietetic Products 2010 |
| Reduce incidence and duration of common infectious diseases (upper respiratory tract and gastrointestinal) | Children, adults | King et al. 2014 |
| Prevent antibiotic-associated diarrhea | Children, adults | Goldenberg et al. 2015 |
| Extend remission of ulcerative colitis | Adults | Naidoo et al. 2011 |
| Improve therapeutic efficacy of antibiotic treatment of bacterial vaginosis | Adult women | Martinez et al. 2009 |
| Reduce low density lipid cholesterol | Adults | Jones et al. 2012 |
| Prevent Clostridium difficile diarrhea | Children, adults | Goldenberg et al. 2017 |
| Reduced prevalence of dental caries and gingivitis | Infants, children | Martin-Cabezas et al. 2016 |
Additional information:
- Infographics on “Probiotics”, “Fermented foods” and “How to read a dietary supplement label” available from the International Scientific Association for Probiotics and Prebiotics (ISAPP)
- Short, informational videos on probiotics from ISAPP
- Fermented Foods webpage available from ISAPP
- Fermented food and nutritional guidelines. Blog post by Mary Ellen Sanders
- Health Benefits of Fermented Foods. Blog post by Mary Ellen Sanders
- Finding a High-Quality Probiotic Food. Blog post by Mary Ellen Sanders
- Is it time for live cultures to be included in official dietary recommendations? (2017) Nature Café, London. 15-min lecture by Mary Ellen Sanders.
- 30-min webinar sponsored by Medscape. Navigating the World of Probiotics. Helping Patients Make Good Choices. Originally aired April 17, 2018.
- Hill C and Sanders ME. 2013. Rethinking “probiotics”. Gut Microbes. 4(4):269-270.
- Marco ML, Heeney D, Binda S, Cifelli CJ, Cotter PD, Foligne B, Ganzle M, Kort R, Pasin G, Pihlanto A, Smid EJ, Hutkins R. Health benefits of fermented foods: microbiota and beyond. Current Opinion in Biotechnology 2017, 44:94–102.
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Mary Ellen Sanders, PhD
Mary Ellen Sanders, PhD was the founding president and is currently the executive science officer of the scientific society, ISAPP. ISAPP – the International Scientific Association for Probiotics and Prebiotics – is a non-profit organization dedicated to advancing the science of probiotics and prebiotics. Dr. Sanders received her B.S. in Food Science at University of California – Davis, and her M.S. and Ph.D. in Food Science with an emphasis in microbiology at North Carolina State University in Raleigh.
