Benefits of Prebiotics

Best Prebiotic foods and fibersYou’ve heard of probiotics – the beneficial yeasts and bacteria that have a huge impact on human health. These microorganisms live in the gastrointestinal tract where they help to support the digestive system, regulate immune reactions, control inflammation throughout the body, help to burn fat, and more. Because they are living beings, probiotics need to eat.

Guess what they like to feed on?

You got it. Prebiotics.

What Are Prebiotics?

Prebiotics are types of food fibers that resist digestion in the upper digestive system (mouth, stomach and small intestine). They make it to the large intestine where probiotic bacteria and yeasts ferment or “eat” them. For a fiber to be considered a prebiotic it must:

  • Resist digestion by stomach acid and enzymes
  • Not be absorbed in the stomach or small intestine
  • Be fermented by beneficial intestinal microflora (probiotics)
  • Stimulate the growth or activity of beneficial bacteria, yeasts or fungi [1]

NOTE: According to a national health study, less than 3% of Americans are eating the recommended daily intake for total fiber, and the most popular fiber sources are not prebiotic [5].

Prebiotics and Dysbiosis

Without prebiotics to eat, probiotic bacteria and yeasts die off, creating room for “bad” or pathogenic bacteria, yeasts and fungi to adhere to the intestinal wall. This kind of overgrowth is called dysbiosis – a state of imbalance between the “good” and “bad” bugs in the gut. The bad guys release inflammatory chemicals, injure the gut wall, and prevent absorption and creation of nutrients.

Dysbiosis has been linked with diseases of the gastrointestinal system, as well autoimmune conditions, cardiovascular disease, mental health conditions and more. Providing food in the form of prebiotic fibers can help to boost populations of beneficial microbiota in the colon, allowing them to fight off the bad guys and return balance to the gut environment.

Prebiotics and Intestinal Hyper permeability

Also known as leaky gut, intestinal hyper permeability occurs when the cells of the large intestine are unable to maintain the tight gap junctions that bind them together. This forms “leaky” in the colon wall. Toxins, “bad” bugs, and waste can slip through these gaps and find their way into the blood stream, resulting in a long list of health issues.

People often take probiotic supplements [link to probiotic article] in an effort to support gut health and repair the intestinal barrier, but that’s only one piece of the puzzle. Remember – probiotics need something to eat! Prebiotics can help to heal leaky gut.

Probiotics Digest Prebiotics through Fermentation

The process of probiotics “eating” prebiotic fiber is actually an act of fermentation. This produces beneficial byproducts such as short-chain fatty acids (e.g. butyrate, acetate and propionate) and gases (e.g. hydrogen and carbon dioxide). The short-chain fatty acids feed nearby intestinal cells. When the colon cells are healthy they are able to tighten up their gap junctions and heal leaky gut. Short-chain fatty acids also providing a valuable energy source – they give us ~10% of our average daily caloric requirements! [4] Gases destroy any bad bacteria and yeasts hanging around – and can cause unwanted side-effects of flatulence, bloating, discomfort and loose stools in some people [3].

Research is looking at the short chain fatty-acids produced by prebiotic fermentation to treat:

  • Metabolic syndrome
  • Chron’s disease
  • Ulcerative colitis
  • Antibiotic associated diarrhea
  • Certain cancers [3]

A huge meta-analysis of studies between 1947 and 2017 concluded that synbiotics (probiotics and prebiotics taken together) could reduce inflammation, not just in the gut but throughout the whole body [2].

BOTTOM LINE: To get the most out of your probiotic supplement, boost your intake of prebiotic foods.

Healthy prebiotic fibers

Three Key Prebiotic Fibers

There are three main types of potent prebiotics that are available from food sources: inulin, fructo-oligosaccharides, and resistant starches.

1. Inulin

Inulin is a soluble fibre made of 20 fructose molecules and one glucose molecule. Because of this long chain of fructose molecules, inulin can’t be absorbed in the small intestine so it makes its way to the large intestine where it can act as a prebiotic.

Inulin fibre foods that have proven prebiotic activity include: Other sources of inulin which may have prebiotic activity:
  • Onions
  • Wheat
  • Jerusalem artichoke
  • Chicory root
  • Leek bulb
  • Asparagus
  • Rye
  • Watermelon
  • Zucchini
  • Mango
  • Peach
  • Persimmon
  • Rambutan

Table sources [1] [6]

2. Fructo-Oligosaccharides (FOS)

Like inulin, fructo-oligosaccharides (FOS) are made of mostly fructose molecules and are difficult to digest and absorb, allowing them to pass through the digestive system to feed the colonic bacteria.

FOS fibre foods that have proven prebiotic activity include: Other sources of FOS which may have prebiotic activity:
  • Jerusalem artichoke
  • Shallots
  • Red onion
  • Asparagus
  • Chicory root
  • Garlic
  • Onion
  • Soybeans
  • Whole-grain corn
  • Ripe bananas
  • Endive

Tables sources  [1] [6]

3. Resistant Starches

The starch in these foods is considered “resistant” because it resists digestion – the first classification for what makes a fibre a “prebiotic”, right? These intact starches make their way to the large intestine where they have been shown to feed probiotic bacteria, yeasts and fungi in the colon.

Resistant starch foods that have proven prebiotic activity include: Other sources of FOS which may have prebiotic activity:
  • Green or under-ripe bananas
  • Sorghum
  • Green plantains
  • Retrograde starches
  • Cooked & cooled potatoes
  • Cooked & cooled rice
  • Cooked & cooled pasta
  • Canned kidney beans (served cold)
  • Canned chickpeas (served cold)
  • Whole grain brown rice
  • Lentils
  • Bulgur
  • Pearl barley

Table sources [1] [6] [7]

CAUTION: Speak to a qualified nutritionist for personalized advice before making any sudden changes to your diet.

Rich prebiotic foods

Five Easy Foods to Boost Your Prebiotic Intake

Inulin, FOS and resistant starches are key prebiotic fibres to help support the health of your gut microbiome. Here are five easy ways to boost prebiotics in your diet while you are healing your gut and taking probiotic supplements:

#1 Onions

Onions are probably the cheapest, easiest, and arguably tastiest way to pack more prebiotics into your diet. They contain huge amounts of both inulin and FOS prebiotic fibers – more-so when they are eaten raw, fermented or pickled, but there are still plenty of prebiotics present once onions are cooked. Red salad onions are particularly high in FOS, while brown onions are richer in inulin – both stimulate the growth of beneficial bacteria and yeasts in the gut.

#2 Garlic

Garlic is rich in FOS prebiotics. Because their cloves are small, you may have to eat a lot of garlic to get much prebiotic fibre but studies have confirmed that even a small amount of garlic stimulates the growth of Bifidobacteria probiotic strains in the colon [8] – eating a little garlic every day is an easy way to support your good gut bugs. Plus, it’s really tasty and readily available!

#3 Cold Potatoes, Rice & Pasta

A form of resistant starch is called “retrograde starch”, and these cold carbohydrate foods are full of it – but only if they are cooked and then cooled before eating. During the cooling period, their starches re-assemble in a slightly different molecular shape which resists digestion. Because they are resistant to digestion and absorption, these starches make their way to the large intestine where they act as prebiotic food for probiotics. Potato salad, anyone?

#4 Leeks

Leeks are related to the garlic and onion family, so it makes sense that they’re packed with prebiotics too. In fact, leeks contain up to 15% of inulin prebiotic fibre. Be sure to use the bulb of the leek (the white part rather than the green leaf) as this is where the prebiotic fibre is found.

#5 Jerusalem Artichokes

Also known an sunchokes, earth apples, and topinambour, Jerusalem artichokes are packed with inulin prebiotic fibre. They are often used as potato substitutes for people with diabetes (did you know that inulin can help to control blood sugar levels?), so try steaming, mashing, boiling or even baking them for a big hit of prebiotics.

CAUTION: Prebiotic foods are NOT suitable for people on a Low FODMAPS diet. Speak to a nutritionist for personal advice on how to support your gut bacteria while avoiding prebiotic foods.

NOTE: There are many other types of food fibers that aren’t prebiotic. While they may not feed probiotics, they all help to improve gut health by adding bulk to the stool, improving stool transit time (technical term for “they can make you more regular”), lowering inflammation, trapping and eliminating pathogenic bacteria out of the gut. Eating prebiotic foods will help to support probiotics, but don’t get stuck on the details – a high-fibre diet is good for your gut and your general health!

Further Reading:

  • [1] Slavin, J. (2013) Fiber and Prebiotics: Mechanisms and Health Benefits. Nutrients., 5:4, 1417 – 1435.
  • [2] McLoughlin, R. F., et al. (2017) Short-chain fatty acids, prebiotics, synbiotics, and systemic inflammation: a systematic review and meta-analysis. Am J Clin Nutr., 9.
  • [3] den Besten, G., et al. (2013) The role of short-chain fatty acids in the interplay between diet, gut microbiota, and host energy metabolism. J Lipid Res., 54:9, 2325 – 2340.
  • [4] Bergman, E. N. (1990) Energy contributions of volatile fatty acids from the gastrointestinal tract in various species. Physiol Res., 70:2, 567 – 590.
  • [5] McGill, C. R., et al. (2015) Ten-Year Trends in Fiber and Whole Grain Intakes and Food Sources for the United States Population: National Health and Nutrition Examination Survey 2001–2010. Nutrients., 7:2, 1119 – 1130.
  • [6] Roberfrold, M. (2007) Prebiotics: The Concept Revisited. The Journal of Nutrition, 137.
  • [7] Salijata, M. G., et al. (2006) Resistant starch – a review. Comprehensive Reviews in Food Science and Food Safety, 5,
  • [8] Zhang, N., et al. (2013) Study on prebiotic effectiveness of neutral garlic fructan in vitro. Food Science and Human Wellness, 2:3, 119 – 123.
About James Lyons

James Lyons (BHSc Nutritional Medicine) is a clinical nutritionist, medical writer, and educator. He specialises in plant-based nutrition and is passionate about improving public access to reliable and accurate health information.

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