Prebiotics Part 1: Prebiotics for Internal Fermentation

Fermentation Outside the Body

Much has been said about fermentation outside the body in terms of fermented foods and drinks. (I love to learn, write, and present about food fermentation!) If my taste buds could talk, they would be begging for more flavourful fermented foods, such as sauerkraut, kimchi, bread, vinegar, beet kvass, and pickles. These foods are fermented by lactic acid bacteria (LAB). In its simplest form, fermentation converts carbohydrates to CO2 and acids, producing characteristic tangy flavours. A dietitian’s dream food, ferments are a nutritional powerhouse multiplying existing nutrients in the starting vegetables, creating new nutrients, particularly B vitamins and vitamin K2, while disarming anti-nutrients that would otherwise bind minerals, such as iron, magnesium, and zinc. These benefits are the product of lactic acid fermentation.

Fermentation Inside the Body

In a similar fashion, fermentation also occurs inside the body by the bacteria that reside in the intestine, particularly the colon. The main substrates for bacterial fermentation in the intestine are carbohydrates that humans cannot digest. When these substances are fermented, bacteria produce gas (not the greatest part of internal fermentation) and short-chain fatty acids (SCFA) that are known for anti-inflammatory effects, reducing cholesterol, and serving as an energy source for colon cells. Protein is also fermentable by bacteria, yet its end products, including ammonia, amines, phenols, and sulfides, are potentially harmful if not promptly cleared from the intestine. Thus, the health benefits associated with intestinal fermentation are related to bacteria that utilize certain carbohydrates, namely prebiotics.

Prebiotics Defined

Simply stated, prebiotics are “food” for bacteria residing in the gastrointestinal tract. Carbohydrates that are non-digestible by humans in the small intestine or are partly absorbed will continue through the intestine to the colon for fermentation by bacteria. Unlike humans, bacteria have enzymes for processing these food substances, thereby utilizing what would otherwise pass through the body unchanged. This is a win-win for bacteria and us: bacteria get “fed” from our leftovers, and we receive health benefits from having healthy bacteria living in the intestine.

Prebiotics in a more technical sense 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” (Gibson et al. 2010). For food substances to qualify as prebiotics, three criteria must be met.

  1. It resists the harsh, acidic conditions in the stomach and digestion in the small intestine, which is where most foods are split into smaller components by enzymes, then absorbed across the intestinal lining for use by our cells. However, humans lack enzymes in the small intestine to digest certain carbohydrates. Many of these carbohydrates are fibres, but not all forms of fibre are prebiotics. Two other criteria must be met to gain prebiotic classification.
  2. It is fermented by intestinal microbiota. Not all non-digested substances that reach the colon will be fermented, so these would not be prebiotics. Although bacteria ferment many undigested food substances, some substances will remain undigested and add to other waste products that form stool. Those substances that escape digestion in the small intestine and are fermented by bacteria in the intestine may qualify as prebiotics if the third criterion is met.
  3. It selectively stimulates the growth and/or activity of intestinal bacteria associated with health and wellbeing. If prebiotics stimulated pathogenic, or harmful bacteria, prebiotics would be on par with refined sugar – something I would recommend eliminating from your diet! If prebiotics reduced bacterial diversity and abundance – something associated with certain diseases – we would all want to avoid prebiotics. I would not be writing this article; you would be reading something more relevant. But because prebiotics stimulate the growth and activity of beneficial bacteria, we can expect improved health when we consume prebiotic-rich foods.

Prebiotic-rich foods, please!

Knowing the criteria for prebiotics, let’s get to the practical food part. Food that contain rich amounts of prebiotics are, sadly, limited. However, weekly meal planning will help you intentionally choose meals that include a variety of prebiotic-rich foods. Varying your prebiotic choices is important because different bacteria thrive off different prebiotics. Bacteria have “food” preferences too!

Below is a list of 10 prebiotic-rich foods to boost your internal fermentation. Future blogs will expand on the categories of prebiotics. For now, try to plan meals that incorporate more of the ingredients from the list below.

  1. Asparagus – Benefit from the price of asparagus from April to June when it is in-season. Consider buying extra asparagus while the price is hot to ferment for future flavourful. Add asparagus to frittatas, pasta, breakfast hash, stir-fries, potato salads, and soups. Or simply, sauté over medium heat and drizzle with a tahini-garlic dressing.
  2. Jerusalem artichokes – These brown-skinned tubers are not actually artichokes and are not exclusively grown in Jerusalem. These are seasonal in the fall when other root vegetables are harvested. If you’re are looking for these in your grocery stores now, good luck. These are hard to find in urban grocery stores, let alone rural Alberta in the spring. Prepare these vegetables as you would parsnips. Roast in the oven with other vegetables, such as cauliflower or potatoes. Boost the gut benefit of mashed potatoes by boiling and mashing Jerusalem artichokes with potatoes. Add pureed artichokes to soup or risotto, or added to a stir-fry.
  3. Garlic – Okay, garlic breath is not always welcomed, but gum can save you here. Think about how your microbiota will benefit from garlic. Consider roasting a whole bulb of garlic to smear on bread. Add garlic to homemade salad dressings, hummus or other bean dips, and soups.
  4. Leeks – From the allium family, which includes onions, garlic, shallots, scallions, and chives, leeks have a sweet and more delicate flavour than onions. Prebiotics are richest in the bulb, yet the stem has culinary uses too. Use leeks in place of onions in soups, stocks, frittatas, omelets, or sauerkraut. Be sure to clean leeks well as dirt and sand become trapped between the layers. Leeks are in-season in Alberta from September to December, but are normally available in grocery stores year round.
  5. Onions and onion powder – A staple in any kitchen for almost any nutritious dish with flavour. Get chopping!
  6. Dandelion leaves – Not just your hated lawn weed…add to salads or sandwiches, but avoid using dandelion leaves that have been sprayed with chemicals.
  7. Chicory root – For those who are trying to kick their caffeine addiction, you may want to try roasted, ground chicory root as an caffeine-free coffee alternative. Your gut will thank you as it is loaded with inulin, a prebiotic. Most powdered inulin supplements are derived from chicory root. Try this recipe for Chicory Latte.
  8. Rolled oats – Leave the instant and quick-cooking oats on the shelf. Choose either old-fashioned, large-flaked rolled oats, steel-cut oats, or, the least processed of all, oat groats. Top with any combo of hemp hearts, ground flax seed, cacao powder, cinnamon, nut butter, coconut flakes, berries, chopped nuts, or apple sauce.
  9. Whole grains – Most whole grains have prebiotics, so be sure to rotate millet, amaranth, quinoa, barley, rye, wheat, wild rice, and teff into your diet. Barley, rye, and wheat contain gluten and have high amounts of prebiotics when served in less refined sources. If gluten is not a problem for you, I’d recommend pumpernickel bread, grainy barley or wholemeal rye bread. Beware of these wholesome breads made with enriched refined flours.
  10. Green bananas – Yellow bananas won’t be of much benefit to your gut. As bananas ripen, starch is converted to simple sugars, making ripe bananas much sweeter than unripe bananas and reducing the prebiotic richness. Learn from Caribbean cuisine: boil green bananas with the peel on, then cool, peel, slice, and sauté with other vegetables.

Although I recommend whole foods as much as possible like the ones above, there are many processed foods that are fortified with prebiotics. Look for prebiotics under the terms inulin, fructooligosaccharides, or galactooligosaccharies on the ingredients label on the following foods: breakfast cereals, granola bars, meat products, frozen desserts, and diet foods.

Stay tuned for Part 2 in this prebiotic series where I’ll explore the difference between prebiotics, namely fructans, galactooligosaccharies, and resistant starches, with more helpful tips on incorporating foods to boost your internal fermentation.



Gibson GR, Scott KP, Rastall RA, Tuohy KM, Hotchkiss A, Dubert-Ferrandon A, Gareau M, Murphy EF, Saulnier D, Loh G, Macfarlane S, Delzenne N, Ringel Y, Kozianowski G, Dickmann R, Lenoir-Wijnkoop I, Walker C, Buddington R (2010) Dietary prebiotics: current status and new definition. Food Sci Technol Bull Funct Foods 7:1–19.

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