Prebiotics: A Missing Link to Long-Term Gut Health

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The power of probiotics has been all the rage in the last few years, as these beneficial microorganisms have shown to help with various conditions, such as infant colic, eczema, antibiotic-induced diarrhea, acute infectious diarrhea, and even upper respiratory tract infections (1,2).

However, the therapeutic effects of probiotics are transient, as probiotics are not able to recolonise or reseed healthy bacteria populations in the gut. The probiotic strains only remain in the gut for days or, depending on the persistence of the strain, weeks after we stop taking them (3,4).

To ameliorate this issue, we turn to probiotics’ less spoken about, but very powerful counterpart- prebiotics. Prebiotic food sources are able to selectively feed beneficial bacteria to build up health-promoting bacteria populations while also suppressing the bad ones.  To be considered a prebiotic, the food source:

-       Cannot be digested or absorbed in the stomach or small intestine

-       Must act as a food source for one or more beneficial bacteria in the large intestine

-       Must affect the health composition of the colonic microflora ecosystem in a positive way

-       Must induce changes to improve the health of the host (person, animal, etc) (5).

Three of the most studied prebiotics are partially hydrolyzed guar gum (PHGG), galactooligosaccharides (GOS), and fructooligosaccharides (FOS).

Partially Hydrolyzed Guar Gum

One of our favorite prebiotics is less well known, but incredibly effective and with plenty of research to support it! Meet partially hydrolyzed guar gum, not to be confused with guar gum, as these substances are processed very differently in the body.

Guar gum vs. Partially hydrolyzed guar gum (PHGG)

Guar Gum

Guar gum comes from the guar or cluster leaf (Cyamopsis tetragonoloba), and it’s found by separating the endosperm portion of the seed from the husk and germ portion. Guar gum is often used as a thickener and stabilizer in products, such as juice, ice cream, syrup, ketchup, and sauces. Because of its high viscosity, some sources do not consider it a fiber.

Partially hydrolyzed guar gum

Partially hydrolyzed guar gum (PHGG) is a very different substance than guar gum and is also processed very differently in the body than guar gum. PHGG is derived from guar gum by the process of enzymatic hydrolysis. Enzymes such as mannanse, pectinase, and cellulose act on the mannose-mannose link and produce PHGG, which is a low molecular weight and low viscosity galactomannan. Because this newly formed substance cannot be digested by intestinal secretion, it IS considered a dietary fiber (6).

PHGG Use and Benefits as a Prebiotic

Recent research has explored the possibility of using this PHGG fiber as a prebiotic source. In one particular study, six strains of Lactic Acid bacteria were studied with PHGG, and the researchers found that almost all of these strains showed an ability to assimilate PHGG. Streptococcus thermophilus, a bacteria that has many digestive and immunity health benefits, exhibited the highest growth with PHGG among the strains. The researchers concluded that PHGG can be considered a prebiotic source and that it could play a role in growing probiotic bacteria and balancing out gut microflora (6).

Other benefits

  • PHGG has been found to relieve constipation just as well as laxatives do, but with no adverse effects (7).

  • PHGG has been studied in patients with enteral nutrition (tube feeding) and has shown to lower the incidence of diarrhea (8).

  • PHGG has also been useful in treating IBS symptoms (both constipation- dominant and diarrhea-dominant) and has been successful in both adults and children (9,10).

  • PHGG increases bifidobacterium(11,12), as FOS and GOS do.

  • PHGG has promising results for those who have SIBO (small intestinal bacterial overgrowth) as well. A clinical trial found that outcomes for SIBO patients who used rifaximin with PHGG had better outcomes than patients who used rifaximin alone (13).  

  • Importantly, PHGG is often a preferred prebiotic supplement when compared to other prebiotics (14).

Notes on Use

PHGG is a white powder that is almost tasteless and water-soluble. It is easily mixed in a glass of water or smoothie.

The dosage of PHGG can change based on the condition, but we usually recommend 5-7.5g/day. It’s important to start very slow, perhaps at a third of the full dose. After a couple of days, or after any side effects dissipate, slowly increase the dose until you reach the full dose. As always, speak with your healthcare provider to determine what is right for you.

Potential Side Effects

Possible side effects of PHGG may include abdominal discomfort, gas, diarrhea, and cramps, though they tend to be milder with PHGG than other types of fiber (15). These side effects usually dissipate as the intestinal flora adjust.


GOSs are chains of galactose molecules that are found in all mammalian milk. Like FOS and PHGG, they are not absorbed or broken down in the upper GI tract, which allows them to reach the colon.


GOS is found in all mammalian milk. For supplementation, it is derived from lactose by using the enzyme, beta-galactosidase. GOS is found in significant amounts in human breast milk, and recently, it has been added to some infant formulas in an attempt to mimic breast milk. GOS is also found in some foods, such as legumes, Brassica-family vegetables, and pumpkin seeds.


The benefits of consuming GOS through mammalian milk, other food sources,  and supplementation:

  • GOS increases growth of bifidobacteria, which are bacteria that help you digest fiber, produce short-chain fatty acids, and produce important B vitamins (16).

  • Some research shows that GOS also increases growth of lactobacilli bacteria (17).

  • GOS can significantly improve constipation (18).

  • In combination with FOS, GOS has treated and helped prevent atopic eczema in infants (19).

  • GOS has improved IBS symptoms in regard to bloating, flatulence, stool consistency, and anxiety (20).

  • GOS has a protective effect against various gastrointestinal pathogens, such as E.coli (21), Salmonella typhimurium (22), and Vibrio cholerae (23).

  • GOS has improved calcium absorption (24,25).

Notes on Use

GOS as a supplementation is available in a syrup or a powder.

The dosage of GOS depends on the health goal:

  • Increased bifida bacteria have occurred with 2.5- 15 g/day

  • Treatment of IBS is 3.5 g/day

  • Prevention of traveler’s diarrhea is 2.6 g/day

  • Increased calcium absorption is 20g/day (5)

Once again, start with a low dose, and work up to the optimal dose for the target health goal, as your symptoms decrease.

Potential Side Effects

Potential side effects are abdominal bloating, flatulence, abdominal pain, and distension. These effects will lessen over time as the intestinal flora adjust.

GOS is very safe, as it is found in all mammalian milk. Importantly, GOS is often derived from lactose. Because of the way GOS is produced, it does not often present issues for individuals who have a dairy sensitivity. In fact, GOS is being used to adjust the intestinal microflora to alleviate lactose intolerance in individuals (26). However, it is important to go slow with GOS and be under the care of a knowledgeable practitioner.

Fructooligosaccharides (FOS)

FOS is made up of branched chains of fructose and gluctose molecules. FOS is resistant to digestion in the human upper gastrointestinal tract because of the beta configuration of its bonds, whereas the human GI tract requires alpha configurations.  Therefore, FOSs are considered to be non-digestible oligosaccharides.


FOS is found in over 36,000 plant species, including common vegetables, such as chicory roots, dandelions, garlic, leeks, and rye. The most common way of supplementing FOS is inulin, which is created by the hot water extraction of fresh chicory roots.


The benefits of consuming FOS-containing food and supplement sources:

  • FOS increases growth of bifidobacteria, which are bacteria that help you digest fiber, produce short-chain fatty acids, and produce important B vitamins (27,28).

  • FOS, in combination with GOS, has shown to improve immune system response in infants who were given infant formula with prebiotics as opposed to infant formula without prebiotics (29).

  • FOS  increases absorption of minerals, such as calcium and magnesium (30).

  • FOS, in combination with GOS have improved treatment and increased prevention in atopic eczema in infant formula studies (19).

  • FOS promote satiety or feeling full (31).

Notes on Use

You can achieve the same results from consuming FOS through food sources or through supplementation. The recommended dose for adults to see increases in bifidobacteria is approximately 10g/day. It is recommended to start at about 3g/day and slowly work up to the full dose to avoid uncomfortable GI symptoms (5).

In research with infants and toddlers, participants have generally been administered 1-3 g/day.

Potential side effects

FOS benefits often exceed side effects, which include bloating, flatulence, and discomfort. These side effects often are dose dependent, and usually decrease over time.

There is also a documented anaphylactic allergy to the inulin found in vegetables and some processed foods, though because these items are consumed so widely, it appears to be very rare (32).

Concerns have been raised about FOS increasing the presence of Klebsiella pneumonia, which is a pathogenic bacteria that can cause trouble if it travels to other parts of your body. However, FOS has increased K. pneumonia growth only when K. pneumonia was grown in a Petri dish in isolation, not in the presence of other bacteria, which is more like the human GI tract (33).

However, clinically, we have had mixed results with inulin, especially in patients with autism. On one hand, some patients with autism have seen reversal of symptoms with the use of inulin, but on the other, we have had patients with autism who flare with the use of inulin.

Other foods that may benefit intestinal flora:

Other groups of foods are prebiotic-like in nature, as they are able to make their way to the colon to feed good bacteria groups, but they do not always selectively feed good bacteria, as true prebiotics do. Even so, these foods have shown to positively affect change in the microbiome. These include polyphenols (34), which are phytochemicals found in fruits, vegetables, legumes, tea, coffee, and chocolate. They are mostly known for their antioxidant properties, but they are also known to increase good bacteria, such as bifidobacteria and lactobacilli (34).  

Another food source is resistant starch foods, such as legumes, red kidney beans, and less ripe bananas. These foods have also shown to improve colonic health and increase bifidobacteria and lactobacilli bacteria (35). To see a more complete chart of prebiotic and prebiotic-like food sources, see the table below.

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Our recommendation:

Upon starting the use of prebiotics to improve your intestinal flora, we recommend to start a low dose of PHGG (⅓ of the recommended dose) and work your way up to full dose (5-7.5 g/day). Once again, only increase your dose when any side effects have dissipated. After you are regularly taking PHGG with no side effects, you can move onto FOS and GOS prebiotics, once again starting at low doses (see dosage information above) and working your way up.

In general, we think it’s best to be mindful of what prebiotic or prebiotic-like foods you are consuming with each meal. A diet with a diverse range of prebiotic, fibrous foods will result in a healthier and diverse microbiome and a happier, better-functioning you!

Works cited:





  5. Hawrelak, J. (2013). Prebiotics, synbiotics, and colonic foods In M.M. Pizzorno J (Ed.), Textbook of natural medicine, 4th ed (pp. 966-978).































Ryan Vermeesch