What role does FOS play in maintaining healthy gut flora?

FOS is an abbreviation for Fructooligosaccharide, it is a soluble fibre or a prebiotic.  Its name means that it is a compound containing between two and ten simple sugars (or monosaccharides), which in this case are fructose molecules.

In the digestive system FOS resists hydrolysis (break down) by salivary and intestinal digestive enzymes.  Once in the colon it acts as soluble fibre and is fermented by anaerobic intestinal bacteria.  In particular FOS is thought to stimulate the growth of Bifidobacteria species which are considered friendly or beneficial and which help to improve host health.  FOS produces short chain fatty acids such as butyrate – that provide 70% of the energy used by the colon cells.

With fermentation by beneficial bacteria the pH of the colon is reduced, making the environment more acidic. FOS may initially also feed the less beneficial bacteria in the colon but the change in pH is not agreeable to them and will hopefully soon lead to a reduction in their numbers.  The increase in acidity also improves mineral solubility meaning that nutrients such as calcium, magnesium, iron and zinc are more easily absorbed into the blood stream. Great news!

Beneficial bacteria will produce greater amounts of acid and smaller amounts of gas while they are fermenting, compared to the less desirable strains of bacteria that produce less acid but a lot more gas.  This is why FOS is said to be helpful for issues with bloating or flatulence, to help reduce these undesirable symptoms.  It is also why people may experience some issues with gas production when they first start to use FOS as, before the pH of the colon has had a chance to become more acidic, both types of bacteria will be benefitting from the nutritional boost.  If this issue does arise it should decrease after a week or two and is a sign that the FOS was needed.

The product is most often produced by extraction from inulin (a polysaccharide/chain of fructose molecules /type of soluble dietary fibre) in chicory root. It is suggested to start a supplementation programme with 2-5g/day and to build up to 10g/day over a two week period.

FOS has a sweet taste, and is even used quite widely as a sweetener, but due to the body’s limited ability to process fructans (the chain of fructose molecules) it has minimal impact on blood sugar.


This information comes from a recently attended seminar Gut Instinct; the ecosystem by Nigel Plummer PhD, microbiologist who designs supplements for nutraceutical companies such as BioCare.  He is also managing director of Cultech.  Further article references are available if required.

About Katie Clare

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2 Responses to What role does FOS play in maintaining healthy gut flora?

  1. Hey Katie
    Great to see your blog! Do you fancy writing for the Funky Raw magazine? I’d love to get more fermented food in there…

  2. katie says:

    Sure. Let’s talk.

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