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A Short Guide To Oligosaccharides (FOS, GOS & More)

Researched and Written by:
Richelle Godwin, RDN Richelle Godwin, RDN

Oligosaccharides may be one of the most important types of prebiotic fiber.  From fructooligosaccharides (FOS) to less sexy ones like AXOS, there's a bit to unpack.  Let's explain it all.

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Table of Contents

    What are oligosaccharides?


    • Indigestible carbohydrates made up of 3-9 saccharide or “sugar” have traditionally been classified as oligosaccharides. S  
    • Oligosaccharides may offer physiological benefits such as increased stool volume, improved bacterial fermentation in the colon, accelerated colonic transit, reduced blood cholesterol, and improved after-meal blood sugar control. S 
    • Many prebiotics belong to the group of nondigestible oligosaccharides, which resist digestion and absorption in the human small intestine and are fermented in the large intestine. S
    • Examples of common oligosaccharides are listed below:
    • Fructooligosaccharides (FOS)
    • Galactooligosaccharides (GOS)
    • Xylooligosaccharides (XOS)
    • Arabinoxylooligosaccharides (AXOS)
    • Soybean Oligoosaccharides

    Fructooligosaccharides (FOS)

    • Fructooligosaccharides (FOS) are oligosaccharides that occur naturally in plants such as onion, chicory, garlic, asparagus, banana, artichoke, and others. S They are made up of linear chains of fructose units. The number of fructose units ranges from 2 to 60. Dietary FOS are not broken down in the small intestine, meaning they reach the colon intact. FOS have important beneficial physiological effects such as a prebiotic effect and  improved mineral absorption. S 

    Galactooligosaccharides (GOS)

    • GOS is a prebiotic fiber found in foods such as legumes and beans. It may be synthesized in supplement form from soybeans or lactose which is derived from cow’s milk.  S 
    • GOS is also known as oligogalactosyllactose, oligogalactose, oligolactose, or transgalactooligosaccharides (TOS). S 

    Xylooligosaccharides (XOS)

    • XOS are sugar oligomers made up of xylose units, which appear in bamboo shoots, fruits, vegetables, milk, and honey However, there are no reports available on the exact quantity of XOS present in these sources. S 
    • Xylooligosaccharides have been found to have prebiotic potential. S

    Arabinoxylooligosaccharides (AXOS)

    • AXOS is a prebiotic fiber produced from arabinoxylan S which is derived from the cell walls of cereal grains and bran. 

    Evidence Based

    An evidence hierarchy is followed to ensure conclusions are formed off of the most up-to-date and well-designed studies available. We aim to reference studies conducted within the past five years when possible.

    • Systematic review or meta-analysis of randomized controlled trials
    • Randomized controlled trials
    • Controlled trials without randomization
    • Case-control (retrospective) and cohort (prospective) studies
    • A systematic review of descriptive, qualitative, or mixed-method studies
    • A single descriptive, qualitative, or mixed-method study
    • Studies without controls, case reports, and case series
    • Animal research
    • In vitro research

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