By Dr. Karen Scott, Ph.D.

Everywhere you look there is an article or podcast or TED Talk about how important our colonizing microbes are to our health. But, like the weather, although everyone is talking about it what can we do about it? Prebiotics are a promising way to shape our gut microbiota (the term used for the total community of microbes colonizing your body) to be healthier for us. However they are not an alternative to a diverse healthy diet. Eating whole grains, fruits and vegetables, and other fibre-rich foods can also help boost numbers of our ‘healthy’ microbiota, and in turn contribute to gut health.


A prebiotic is a substrate that is selectively utilized by host microorganisms conferring a health benefit. In 2017, ISAPP convened a consensus panel and updated the concept of prebiotics to encompass advances in microbiome science. See Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics, which is available open access from Nature Reviews in Gastroenterology and Hepatology.


prebiotics infographicPrebiotics are indigestible by human enzymes and thus serve as food in our gut for the beneficial colonizing microbes – the ones that live there all the time. By providing them meals, we can encourage the healthier members of microbiota to grow and metabolize foods, and in the process make us healthier.


Prebiotics are naturally found in some plants, such as onions, garlic, bananas, chicory root and Jerusalem artichokes, but typically are present at low levels. To increase your daily dietary intake, include prebiotic supplements or foods with added prebiotics. Prebiotics are sometimes added to yogurts, cereals, breads, biscuits/cookies, desserts or drinks. The word ‘prebiotic’ is seldom used on the label. Instead, look in the ingredients list for Galacto-oligosaccharides (GOS), Fructo-oligosaccharides (FOS), Oligofructose (OF), Chicory fibre or Inulin. Try to get at least 5 grams of prebiotics in your diet every day for improved gut health.


Prebiotics are also present in mother’s milk. These human milk oligosaccharides are thought to enhance the population of bifidobacteria present in the infant gut as well as discourage pathogens that may cause infections in infants. Many brands of infant formula are now supplemented with oligosaccharide prebiotics to mimic this effect.


You will also find prebiotics in some pet foods, both in the kibble and as pill-like supplements. Again they are added to enhance the growth of healthy gut bacteria in your pet’s microbiome.


Although there are more studies published to date on probiotics than prebiotics, prebiotic research is expanding. Established health benefits of some specific prebiotics relate to (1) improving calcium absorption, (2) modifying the glycemic index, and (3)  enhancing colonic bacterial fermentation thereby reducing gut transit time. Such physiological benefits have positive effects on osteoporosis, diabetes and colorectal cancer, respectively. In fact the European Food Safety Authority in positive opinion statements recently acknowledged that “increased consumption of native chicory inulin can increase stool frequency” and that “consumption of foods containing non-digestible carbohydrates instead of sugars [such as inulin and FOS] induces a lower blood glucose rise after meals compared to those containing sugars”.


New research is investigating how prebiotics might be used in the management of gut diseases like inflammatory bowel disease (ulcerative colitis and Crohn’s disease) and irritable bowel syndrome, and even obesity. In the future, specific prebiotics could be designed to boost numbers of specific bacteria known to be less abundant in certain diseases.


Contrary to common belief, we really know very little about how prebiotics impact probiotics that we might take at the same time. It is clear that there is considerable potential for prebiotics to feed probiotics, but few studies have actively demonstrated this. The combination of prebiotic and probiotic has to be carefully considered if the goal is to enhance probiotic growth with the co-administered prebiotic. Laboratory studies are not always accurate in determining if the probiotic bacterium can actually utilize the prebiotic substrate when competition with the diverse resident gut microbiota is considered. More research is required to demonstrate these effects properly.


Dietary fiber can be split into two categories – soluble fiber which is fermented by gut bacteria, and insoluble fiber which is not fermentable and acts as roughage. Although prebiotics fit the chemical definition of a soluble fiber, not all fibers are prebiotics, because they are not all metabolized by beneficial gut microbes.


Individuals who are interested in gut health are often also interested in fermented foods and probiotics. Learn more about they affect human microbiomes in the following links:
A word about Fermented Foods.
A word about Probiotics.


About the author: Karen Scott, PhD, is a Senior Research Fellow at the Rowett Institute of Nutrition and Health at the University of Aberdeen, Scotland. Her research focuses on beneficial members of the gut microbial community.

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