Prebiotics: What You Need To Know

by | Oct 22, 2018 | Blog, General Wellness, Gut Health, Nutrition | 0 comments

What are Prebiotics?

You may be familiar with probiotics, the friendly bacteria that we get from certain foods and supplements. Probiotic supplements are increasingly popular, and with good reason. Populating the gut with enough good bacteria supports digestion and proper immune function, helps us to ward off harmful bacteria, yeast, and other pathogens, and even influences our mood and cognitive function.

If you’ve already got your probiotic intake taken care of, it may be time to talk about prebiotics. Prebiotics are various kinds of non-digestible fiber compounds that feed the good bacteria in our guts. Prebiotics and probiotics work synergistically to build and support a balanced gut microbiome that is critical for overall health. 

There are a few different categories of prebiotics including inulin, oligosaccharides, galactooligosaccharides, and fructooligosaccharides (FOS).

One thing that prebiotic fibers all have in common is that our bodies can’t break them down. Instead of being digested the way most foods are, these dietary fibers bypass the small intestine and end up in the colon. There, our gut bacteria– especially strains like bifidobacterium and lactobacilli that are known to be beneficial– get to feast on them to support their own survival and growth (1). This involves a fermentation process. 

Health Benefits of Prebiotics

The balance of the gut microbiome (our massive internal community of bacteria and other microorganisms) influences the health of the whole body, and supporting gut health with both prebiotics and probiotics can help to improve immune system health (2), decrease inflammation throughout the body (3), support mood and hormonal balance (4, 5), improve various metabolic functions, and reduce the risk of numerous chronic illnesses including type 2 diabetes and cardiovascular disease (6).

A healthy gut microbiota supported by prebiotics can help to regulate blood sugar levels, reduce the risk of obesity (7), normalize cholesterol levels (8), limit incidence and symptoms of some allergies, reduce the risk of autoimmune reactions, improve mineral absorption (9) including magnesium, iron, and calcium, and improve digestive health and gastrointestinal symptoms (10).

Prebiotics have been shown to have anti-inflammatory, antioxidant, and even anti-cancer properties, potentially both protecting against certain kinds of cancer and reducing the incidence of cancer cells (11), (12).

We’re also learning more and more about the gut-brain connection, and the many ways that the gut microbiome and balanced gut flora influences mood, stress response, and emotional regulation (13). Prebiotics have been shown to lower levels of cortisol (14) (often referred to as the “stress hormone”), improve levels of positive mood chemicals like serotonin, and impact behaviours and emotions associated with depression and anxiety (15, 16).

Past, Present, and Future of Prebiotics

The term “prebiotic” was introduced in 1995 by two scientists who learned that giving food to beneficial bacteria in order to support their growth may have been a more effective approach to improving and maintaining gut health than directly increasing populations of the same bacteria.

Their early definition of “prebiotic” consisted of certain criteria: prebiotics had to be non-digestible, and they had to specifically stimulate the growth or activity of bacterial strains in the colon that would affect us in beneficial ways.

As more research comes out about prebiotics, probiotics, the microbiome, and the overall impact of the gut on health, experts in gastroenterology are reviewing the definition of prebiotics, and have recently expanded it to make room for the pieces of the puzzle that we’re still filling in (18).

The new, broader definition of prebiotics makes room for the fact that we don’t know everything there is to know about which bacterial strains are beneficial and which are not, as well as the idea that some prebiotics may feed beneficial microbes in places other than the large intestine (colon).

This new definition is an exciting one, as it opens the door to even bigger ideas and more research about prebiotics, the microbiome, and our overall health.

How to Make Sure You’re Getting Enough Prebiotics

There are a number of prebiotic-rich foods that are pretty easy to build into most diets, and many of them are also high in other important nutrients. Most vegetable sources of prebiotics are best consumed raw as they lose some of their fiber content when cooked.

Prebiotic Food Sources Include:

-Raw chicory root

-Raw onion; leeks

-Raw garlic

-Legumes including chickpeas, beans, and lentils

-Asparagus (best raw)

-Spinach & other leafy greens

-Raw Jerusalem artichoke

-Raw honey

-Raw dandelion greens



-Whole grains

Eating prebiotic foods together with probiotic foods like yogurt, kefir, sauerkraut, and other fermented foods may help to enhance their effects. Even if you’re eating them separately, it’s important to get enough of both– prebiotics are not of much use without probiotics to feed!

There are options available for prebiotic supplements, as well as “synbiotic” supplements containing both prebiotics and probiotics. Prebiotic supplements can be a little hard on the digestive system at first, as we may not be used to consuming large quantities of non-digestible compounds all at once, so it’s best to start slowly. It’s also important to drink lots of water when taking prebiotics or eating prebiotic-rich foods, in order to reduce the risk of digestive side effects.

Should you Avoid Prebiotics If You Have SIBO or Are Following a Low FODMAP Diet?

For many people, the names of prebiotic food categories like “oligosaccharides” and “fructooligosaccharides” are probably vaguely alien sounding. But if you have small intestinal bacterial overgrowth (SIBO), irritable bowel syndrome (IBS), and/or are following a low FODMAP diet, you may be familiar with these words: they’re the things you’ve been advised not to eat. You may have also noticed that many of the prebiotic-rich foods on the list are actually high FODMAP foods like garlic and onion that you’ve trying to avoid, and, well, you’re right.

Prebiotic supplements and many dietary prebiotics can actually cause symptoms like bloating or constipation to worsen for those with SIBO (Small Intestinal Bacterial Overgrowth) or FODMAPS intolerance. Why? Well, if you have an overgrowth of bacteria that you’re trying to control, consuming foods that feed bacteria is exactly the opposite of what you want to do.

If you’re not sure, you may want to start by slowly increasing your prebiotic intake and observing your symptoms and the way you feel. And luckily, there are also some prebiotic-containing foods that are lower in FODMAPS, and may be more easily tolerated if you’re following a low-FODMAP diet.

Low-FODMAP Prebiotic Foods Include:


-Bananas (unripe)


-Canned lentils


-Fennel bulb



Jumping into taking a prebiotic supplement is not recommended if you have (or think you may have) SIBO or IBS, as they can be especially hard on your digestive system. But don’t give up on the concept altogether, as prebiotics have been found to improve symptoms of IBS. It’s all about finding balance.

For more personalized guidance, request a consultation with Dr. John Gannage, MD.

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