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What are Oligosaccharides and Why are They Healthy?

So many gut-support and probiotic products contain ingredients ending in “-oligosaccharides,” most commonly, “fructooligosaccharides” or FOS. At first glance, the “fructo” part may sound bad, like “fructose” as in the dreaded “high fructose corn syrup” additive.

Nutrition chemistry is complex. But we are here to break down the multi-syllabic suffix and teach you which “-oligosaccharides” you should be seeking for overall health.

You likely have consumed members of the oligosaccharide family – they are mildly sweet and tend to have a pleasant mouthfeel, or texture. They are found in onions, leeks, garlic, beans, wheat, asparagus, jicama and are very high in a vegetable called Jerusalem artichoke (which is not an artichoke, but a relative of the sunflower).

Additionally, some key members of the oligosaccharide family are fiber, which is essential to take in to maintain normal gastrointestinal and digestive functioning, chiefly to promote regular bowel movements. Americans tend to consume between one and three grams of oligosaccharides per day – Europeans are said to obtain twice to three times that amount.

Oligosaccharides such as fructooligosaccharides and galactooligosaccharides are known as prebiotics, meaning they serve as nutrition for the trillions of microbes residing in your gut so they can thrive and continue to work on keeping you healthy. More specifically, oligosaccharides that act as prebiotics are fermentable products for certain species of the gut microbiota (a term that means only the bacteria members of the microbiome) and also modulate them.

From 2000 to 2010, there have been numerous studies investigating the prebiotic-specific mechanisms of action of oligosaccharides in the human gut. For example, prebiotic oligosaccharides have been found to modulate colonic beneficial bacteria lactobacilli and bifidobacterial while also inhibiting potentially dangerous bacteria that can cause illness and damage. Research has also shown that they can promote bowel health and regularity, and reduce intestinal issues such as diarrhea and constipation.

Prebiotic oligosaccharides also are known to help you get the most out of your healthy diet by assisting your body to absorb the various nutrients within the foods you eat: they stimulate absorption of iron, calcium and magnesium, for example.

In addition, there have been explorations into targeted health response of prebiotic oligosaccharide, including immune support, and cardiovascular support via managing healthy cholesterol profile.

What are the Top Prebiotic Oligosaccharides?

There are several known potent prebiotic oligosaccharides that are also pretty common, with FOS being the most prevalent.

Here are summaries of the four best prebiotic oligosaccharide.



Typically found naturally in both human and cow milk, galactooligosaccharides (GOS) have made the news recently. In mid-June of this year, the FDA announced it would include galactooligosaccharide as one of eight ingredients under its new legal definition of a dietary fiber. FDA Commissioner Scott Gottlieb, MD, said these eight approvals “are based on a careful review of the scientific evidence suggesting that each of these additional fibers has a physiological effect.”

GOS has merit as a powerful prebiotic. In one human study of 45 volunteers given several prebiotic oligosaccharides or placebo, GOS had interesting results. Those who took it as a supplement showed decreased cortisol levels (through saliva testing), and the researchers said that this suggested that it (and potentially others such as fructooligosaccharides) can positively influence the hypothalamic-pituitary-adrenal (HPA) axis. And GOS may have ability to help people who are high strung or anxious. This same study measured vigilance reaction times, which are high in those who are chronically anxious. Those who took GOS showed decrease vigilance when encountering negative signals compared to those taking placebo; this, said the researchers, indicated that GOS may be associated with decreased anxiety.

GOS in higher doses may cause some GI woes in more sensitive individuals. One study looked at dosages of 3.5 g per day or 7 grams a day of GOS in 44 people with IBS, and found that although the lower GOS dose helped to relieve symptoms such as flatulence and bloating, higher doses seemed to exacerbate them.

Xylooligosaccharide (XOS)


These oligosaccharides are naturally occurring in bamboo shoots, several fruits and vegetables and honey. They are preferred by members of the Bifidobacteria genus. In rodents fed XOS, an increase in Bifidobacterium spp levels in the GI tract was observed. One study sought to find a similar link in humans. The randomized, controlled six-week study looked at the prebiotic effects of XOS (given in a breakfast food) on fecal microbiota in healthy individuals. At the end of the study, those who were taking the XOS had a lower number of microbes called fecal coliforms and a pathogenic bacterium, Clostridium perfringens compared to those in the placebo group. The researchers concluded that the XOS potentially suppressed the growth of Clostridium perfringens via fermenting in the gut, an action that produces short-chain fatty acids (SCFA). SCFA production is known to prevent pathogenic bacteria from colonizing and thus causing illness.

However, if you are taking Lactobacilli – you are wasting your money on XOS, because it does not impact this genus, it only has an affinity with Bifidobacteria.




This type of prebiotic oligosaccharide is obtained from a common yeast called Saccharomyces cerevisiae. Some animal studies have suggested that MOS may help prevent infections in the GI tract. Pathogenic bacteria that reach the intestinal walls often attach themselves there, and MOS has been shown to compete for those binding sites, thus preventing the bad bacteria from settling in. Other studies have shown MOS to stimulate antibody production.




This is by far the most prevalent and many will attest, the most studied of all the prebiotic oligosaccharides. Remember that prebiotic oligosaccharides serve to nourish beneficial microflora, and as such, help them do their jobs more effectively, and even optimally. FOS, naturally occurring, have no calories, do not cause dental caries, are a great source of soluble fiber. They have been shown to improve mineral absorption and to decrease serum cholesterol and another harmful lipid, trialglycerols. Further, according to a scientific review of FOS, consuming this prebiotic oligosaccharide can also augment consistency and frequency of healthy bowel movements, and reduce constipation.
And, it appears that FOS works well with Lactobacillus.

How Do FOS and Lactobacillus Work?

Science shows that a combination of fructooligosaccharides and Lactobacillus are symbiotic – meaning they each enhance one another’s actions; greater than the sum of their parts, so to speak.

One recent study, in fact, showed that FOS and a specific strain of lactobacillus (L. paracasei) had a favorable effect on an increasingly common condition called Non-Alcoholic Fatty Liver Disease (NAFLD). Specifically, the combination reduced several biomarkers indicative of this condition especially when a high-fat diet was normally consumed.

Which are the Best Prebiotics?

It’s not so much that there is a “worst” prebiotic oligosaccharide. The real question should be, “What makes for a best probiotic?”

The best prebiotics, such as fructooligosaccharides, are those that will be effective, surviving the gut and allowing its synbiotic probiotic (for most prebiotics are combined this way) to also survive to attach to the intestinal walls. The optimal dose of FOS, many studies have shown, is approximately 3 grams per day and this is an easy amount to consume.

However, here’s the trick to know: if already blended, each may encourage the other to weaken, so the solution is to blend immediately before consuming. A proprietary technology called “microshot” does this. The FOS is in a liquid base (usually flavored) with its companion probiotic such as Lactobacillus paracasei housed in a protective blister in the bottle’s cap. This unique delivery gives superior stability when compared to similar combinations in traditional delivery forms.

Prebiotic oligosaccharides are easy to incorporate into your daily regimen; as you may not be eating enough to feed your friendly flora.

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