Prebiotics: Another Piece of the Gut Health Puzzle

Prebiotics, perhaps less known than probiotics, are an important piece of the gut health puzzle. We have reviewed in recent weeks how a balanced microbiome, along with probiotics, supports our overall health, particularly digestive health. Prebiotics are a vital component to include in one’s day to day diet for a healthy digestive system.

The definition of prebiotics has been adapted multiple times since first defined in 1995 as “a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria already resident in the colon.” The most current definition, released last month by expert consensus from the International Scientific Association for Probiotics and Prebiotics (ISAPP) simplified the definition to state, “a substrate that is selectively utilized by host microorganisms conferring a health benefit.”

Prebiotics are dietary carbohydrates that are not digested in the gut, but instead are fermented by the bacteria of the gut. As previously stated, our gut consists of various bacteria, bifidobacteria being the most prevalent and thus the most studied in research. Overall, prebiotics promote the growth of certain beneficial bacteria, mainly bifidobacteria and to a lesser extent, lactobacilli. Simply put, prebiotics are food for our microbiota.

What are the benefits of prebiotics?

Some of the health benefits of prebiotics that have been identified include reduction of the occurrence and length of diarrhea due to antibiotic use, a reduction of symptoms and inflammation in people with inflammatory bowel disease (Chrohn’s disease and ulcerative colitis), increased absorption of minerals, calcium in particular, reduced risk of cardiovascular disease, and protective effects on the colon.

Prebiotics are also fiber. Fiber is found in fruits, vegetables, whole grains, legumes, nuts, and seeds. They are a dietary component that is beneficial for health. Overall in the U.S., fiber is under consumed. The recommended daily goal for men is 38 grams and for women 25 grams. According to the USDA, the average daily fiber intake in 2009-2010 was 16 grams — well under the recommended daily goal.

Fiber provides substance to a diet, helping you to feel fuller, which can reduce the amount of food you eat and potentially assist with weight management. Fiber is also vital for healthy gastrointestinal function, reducing constipation, and regulating bowel movements. Eating a high fiber diet has the potential to reduce the risk of cardiovascular disease and type 2 diabetes, and improve blood sugar levels in those with diabetes.

Fiber has so many benefits, yet is it very underutilized in American diets. Besides the advantages listed above, we have the additional benefit of many types of fiber also being prebiotics. To clarify, not all foods containing fiber are considered a prebiotic, but at this point in time all prebiotics are fiber.

Human milk oligosaccharides (HMO)

One of the first prebiotics we are exposed to as infants are the human milk oligosaccharides (HMO) which are found in breast milk. Very little oligosaccharides are found in cow milk or infant formula, but many formula companies are now incorporating galacto-oligosaccharides (GOS) and fructo-oligosaccharides (FOS) into their formulas to try to duplicate the prebiotic benefits found in breast milk.

HMO’s not only promote the growth of Bifidobacterium bifidum, the most prevalent beneficial bacteria in the infant gastrointestinal tract, they are vital in the development of the nervous, immune, and metabolic systems of newborns. They help to establish beneficial bacteria in the infant’s digestive system where their microbiome resides. Additional benefits include hindering pathogens from bonding to the infant’s digestive tract and protection from infections and diarrhea.

Prebiotic fructans

Fructans are a category of prebiotics. Fructans are comprised of inulin, GOS, and FOS. Inulin is naturally found in onions, garlic, leeks, asparagus, whole wheat, bananas, Jerusalem artichokes, artichoke, dandelion greens, and chicory. These foods can easily be incorporated into one’s daily diet. Higher amounts are found in the raw forms of asparagus, garlic, onions, and leeks versus the cooked forms, so make sure to eat a variety of these foods raw and cooked to get the most benefit.

Prebiotics may also be added to many commercial food products including cereals, bread, yogurts, drinks, and supplements. Look for terms such as GOS, FOS, chicory fiber or inulin on product labels to ensure they have prebiotics included.

The majority of prebiotics are bifidogenic, meaning they promote the growth of bifidobacteria. Bifidobacteria are regarded as beneficial to our health. Bifidobacteria is effective for constipation, H pylori infections, IBS, different types of diarrhea, respiratory tract infections and ulcerative colitis.

Lactobacilli, also supported by prebiotics, are likely effective for rotaviral diarrhea and possibly effective for allergic rhinitis, antibiotic associated diarrhea, and atopic dermatitis (eczema) to name a few.

Besides residing in the gut, bifidobacteria and lactobacilli are two types of probiotics that can be purchased in supplement form. As mentioned previously, probiotics are strain specific, so they have very precise actions. No wonder our gut microbiota is predominately made up of bifidobacteria and lactobacilli. Their overall health benefits are astounding!


When you combine probiotics with prebiotics you have synbiotics. Probiotics which are beneficial bacteria, combined with prebiotics, which support the growth of probiotics, make for a winning team

In the United States we have some work to do to increase prebiotics in our diets. Analysis of coprolite, otherwise known as fossilized dung, found that an average male hunter gatherer consumed around 135 grams of the prebiotic inulin per day. Estimates from the U.S. Department of Agriculture’s 1994-1996 Continuing Survey of Food Intakes by Individuals found an average intake of 2.6 grams of inulin per day. The majority of intake was from wheat (70%), followed by onions (23%), with bananas and garlic at 3% each.

Many other “candidates” or potential prebiotics may exist, but more research is needed to confirm their potential beneficial effects on humans. A balanced microbiome is something we should all strive for. Repopulating the gut with probiotics and nourishing those beneficial bacteria with prebiotics may be the key to overall health. We will be keeping our eyes and ears open, and anticipating future research as scientists and researchers expand their knowledge and ours on the health of the microbiome.

by Emily Melby, RDN, Allergy Associates of La Crosse


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