Prebiotic fiber (What it is and where to find it)

Prebiotic fiber, the straight scoop.

The last 15 years have seen an incredible volume of research demonstrating the importance of dietary fiber, and more particularly fermentable prebiotic fiber that benefits friendly bacteria in the bowel. With all of the convoluted information out there, let’s take a clarifying look at what makes a food "prebiotic". I'll also hit on how all dietary fibers affect overall health.

What is Prebiotic?

Prebiotic fibers are food ingredients that feed, grow or activate beneficial microorganisms. The most common example is in the gastrointestinal tract, where prebiotics can enhance the populations of friendly organisms in big ways. Although all prebiotics are fiber of some kind, not all fiber is prebiotic. According to Joanne Slavin, classification of a food ingredient as a prebiotic requires scientific demonstration that the ingredient;
  • Resists digestion and absorption in the upper gastrointestinal tract (small intestines);
  • Is fermented by the intestinal microflora;
  • Selectively stimulates the growth and/or activity of intestinal bacteria potentially associated with health and well-being.

Prebiotics as old as time...

While the concept of prebiotics is relatively new, foods high in prebiotics have been consumed since prehistoric times. Archaeological evidence from dry cave deposits in the Chihuahuan Desert show intense use of desert plants that were high in the plant fiber inulin. Analysis of well-preserved fossilized stool samples (yep, poop) suggests that dietary intake of inulin was about 135 g/day for the typical adult male hunter-forager. Today, it's estimated that Americans get only 15 grams per day.

Where Do Prebiotics Come From? (Insoluble vs. Soluble Fiber)

Unlike probiotics which are living organisms, prebiotic fibers are food ingredients that feed or otherwise benefit the living organisms within us. At first prebiotics were thought to be only soluble fibers, but the club is growing larger land larger as new science uncovers more precisely how the food we eat affects the microbiome.


The word fiber, conjures up images of dense bran muffins and powdery fiber supplements swirled into a glass of fruit juice. This trendy type of fiber found in whole grains, vegetables, coconut flour and supplements galore, is widely acknowledged for its constipation-preventing characteristics. Because insoluble fiber does not dissolve in water, it passes through the gastrointestinal tract relatively intact. So, it can be helpful in promoting regular bowel movements by retaining water and encouraging the passage of food and waste through the intestines. The net effect is speeding up the bowel.

By promptly absorbing and removing irritating agents, carcinogens and even parasites, insoluble fiber systematically cleanses and detoxes the body. What's brand new is that some of these insoluble, non-digestible sources of fiber, also assist your friendly bacteria in doing that thing they do best - lactofermentation. Even psyllium husk ("intestinal brooms") it's been discovered, has some prebiotic effect by providing a substrate for fermentation of lactobacillus and bifidobacteria.


Soluble fibers are a food group whose unique composition breaks down and ferments in the colon. Often this fermentation morphs into a gel-like substance that lubricates the gastrointestinal tract and slows down the bowel to allow for maximum absorption of nutrients. In addition, soluble fibers contain special prebiotic compounds-- the ingredients that the probiotic bacteria in the colon use as “food” or fuel.

Viscous fibers are those that have gel-forming properties in the intestinal tract, and fermentable fibers are those that can be metabolized by colonic bacteria. In general, soluble fibers are more completely fermented and have a higher viscosity than insoluble fibers. However, not all soluble fibers are viscous (e.g., partially hydrolyzed guar gum and acacia gum for example) and some insoluble fibers can actually be well fermented (psyllium).

A little confusion is understandable.

Pectin, the new kid on the block...

Pectin is the latest member to join the family of newly discovered "prebiotics". Its a viscous soluble fiber that's also totally fermentable in the lower bowel.

what are prebiotic and prebiotic foods? According to the USDA, peas and peaches have the highest prebiotic fiber. Then apples, citrus fruits, apricots line up next followed by all other veggies and fruit.
But pectin is more than just a prebiotic fiber. Researchers have long known that pectin can help to lower blood cholesterol levels, particularly very-low-density lipoprotein cholesterol (VLDL) particles which gets converted into low-density lipoprotein (‘bad’ cholesterol) in the blood. In 2010, a team of scientists from University of Illinois suggested that citrus-based pectin is also capable of turning angry, inflammatory immune cells into anti-inflammatory, healing cells that speed up recovery from infection. According to the USDA, peas and peaches have the highest amount (nearly 1 gram per 1 cup serving). Then apples, citrus fruits, apricots line up next with about .5 gram per serving...followed by all other veggies and fruit.

Back to Nature's Design

Inulin and pectin are naturally occurring compounds found in over 36,000 different types of plants and galactooligosaccharides are present in human breast milk-- suggesting that prebiotics are an intricate part of nature’s design that have long been accessible to humans in order to promote optimal health. Yet due to destructive conventional agricultural processes and a changed natural environment, viable sources of prebiotics are somewhat limited in the modern western diet.

Prebiotic compounds can be found in certain foods that are rich in dietary fiber and in undigestible sugars like fructooligosaccharides. Slavin states, "To date, all known and suspected prebiotics are carbohydrate compounds, primarily oligosaccharides, known to resist digestion in the human small intestine and reach the colon where they are fermented by the gut microflora. Studies have provided evidence that inulin and oligofructose (OF), lactulose, pectin and resistant starch (RS) meet all aspects of the definition, including the stimulation of Bifidobacterium, a beneficial bacterial genus. Other isolated carbohydrates and carbohydrate-containing foods, including galactooligosaccharides (GOS), transgalactooligosaccharides (TOS), polydextrose, wheat dextrin, acacia gum, psyllium, pectin, banana, whole grain wheat, and whole grain corn also have prebiotic effects."

Upping the Intake

Studies have shown that Americans have a very low average prebiotic intake, with most of what we do get (70% of it) coming from allergenic wheat-based sources, and another 25% from onions. Expanding our diet to include more fruits and vegetables, nuts and seeds is the optimum way to boost your stack of prebiotic fiber. Keep in mind that cooking foods appears to reduce existing prebiotic content by 25-75%, so consuming foods in a raw state is the better way to go.
Prebiotic fibers in Foods (Inulin/Pectin/Oligosaccharides) Over 36,000 plants contain prebiotic fiber, especially when consumed raw. Here are some with the highest prebiotic value.
  • Herbs – chicory root, burdock root and dandelion root (inulin)
  • Fruits and Veggies – bananas (inulin and OS), peaches, apples, citrus and apricot (pectin)
  • Sweet vegetables – such as onions, garlic, asparagus, leeks and Jerusalem artichokes (inulin)
  • Legumes and grains - peas, corn, wheat (pectin)
  • Raw apple cider vinegar (inulin)
  • Mother’s milk for babies (inulin)
  • Fructooligosaccharides (OS), a subgroup of inulin, is also a prebiotic and is often added to dairy foods and baked goods.
  • Prebiotic supplements - Probiotic Blend (+FOS) and Exodus GI Sponge (inulin from psyllium, and apple pectin) from Tumtree Gut Health.

Other benefits to your health in addition to maintaining your ideal weight are improved immunity and heart health. Prebiotic inulin may be able to moderate cholesterol and triglyceride levels- both indicators of heart disease. Specifically, one study shows that inulin can reduce artherosclerosis, or hardening of the arteries by 30%. In the large intestine and colon, microorganisms degrade pectin and liberate short-chain fatty acids that have positive influence on health.

Benefits that go beyond...

In preliminary Immunity research, prebiotics boost white blood cells and killer T cells, and may even improve your body’s response to infections. Children in one test group who ate yogurt containing inulin had fewer daycare absences, fewer doctor visits and took fewer antibiotics.

Because prebiotics act in your intestines, they have a profound effect on the pathogens and bad bacteria in your body that can cause disease. Prebiotic fiber is now being used to treat childhood obesity, Irritable Bowel Syndrome and Crohn’s Disease, and may also prove useful for treating cancer, osteoporosis and any other diseases connected with the gut.

8 Great Reasons To Get More Prebiotic Fiber In You Now

So, take a fresh look at what you’re feeding your kingdom within, and consider upping your prebiotic intake using some of the sources above… your whole microbiome (700 trillion microscopic hitchhikers) will thank you.

Exodus Prebiotic GI Sponge is our recommendation for upping your intake of prebiotic fiber and strengthening your overall health. 

Want to learn more about healing your stomach pain with prebiotic fiber? Watch this... 


Jonell FrancisHi, I'm Jonell Francis, an expert in Leaky Gut Syndrome, a nerd when it comes to the science of feeling fabulous, and obsessed with guiding women (and those they love) back to vibrant health.
As a mom of many, I’m known for driving tight corners, burning through blenders and overfilling the washing machine. 
But as your health coach, I’ll teach you to lean into your own intuition, trust your gut and embrace crazy beautiful life however it shows up. Best of all, I'll show you my secrets for keeping your family well, all through the year."
Trust me with your health … but not your home appliances!


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