Side Effects of FOS in Probiotics

Beautiful girl with yoghurt
Woman holding a cup of yogurt. (Image: YekoPhotoStudio/iStock/Getty Images)

In recent years, yogurt and kefir have become popular foods because of the medical community's acknowledgment of the benefits of probiotics found in these foods. Probiotics are simply "good bacteria," and probiotic-containing foods can help increase the levels of these bacteria in the gut and decrease harmful microbes, creating a healthier internal environment. A more recent development of probiotic-laden foods such as yogurt is the addition of certain "prebiotics," which are added components that help the good bacteria thrive. They basically serve as food for the beneficial bacteria. FOS is considered a prebiotic.

What Is FOS?

FOS stands for fructo-oligosaccharides, and these sugars linked together in chain formation. Inulin is a popular version of an FOS that is often added to foods with probiotics and is also marketed under the names Neosugar, Alant Starch, Atlanta Starch, Alantin, Dahlin, Helenin and Diabetic Sugar. FOS is found naturally in certain foods, such as asparagus, garlic, Jerusalem artichokes and chicory root.

While simple sugars are digested by your body, FOS is mostly indigestible because humans don't have the enzymes needed to break it down, and so it functions as fiber in the diet. When FOS reaches the large intestine, some of the bacteria that reside there there do have the necessary enzymes and can begin breaking down the FOS and using the components as their own food. The beneficial Bifidobacterium have been reported to use FOS in this way. In this case, FOS acts almost like a fertilizer for certain strains of gut bacteria.

Why Is There Concern About This Ingredient?

The research is quite mixed on FOS, with many studies showing seemingly opposing results. While there is definitely strong support showing that FOS does indeed foster Bifidobacterium colony growth, it could also serve as food for less desirable strains of bacteria. Some studies have indicated that inulin encourages the growth of Klebsiella, a bacterium at work in Ankylosing Spondylitis, which causes problems with intestinal permeability. It also feeds E. coli and many Clostridium species, which are inharmonious with gut-friendly bacteria. There is also a concern that some kinds of yeast are able to use inulin/FOS for fuel, thereby possibly leading to overactive yeast production in the body.

Of additional concern is that many microbes are able to adapt to almost any environment and energy source. Some bacteria were shown to be able to break down and use industrial solvents in the soil. This is not their normal food source, but they adapted and utilized what was available to them. There is concern that "bad" bacteria and fungi could begin to use FOS as a fuel source. Scientists do not fully understand the complex interactions between all the microbes in our bodies, and disrupting the natural balance is concerning. As with any ingredient, there is also potential for allergic reaction; indeed, there is one documented case of inulin causing an anaphylactic reaction.

Reported Side Effects

The list of reported side effects with FOS consumption include flatulence, bloating, cramps, abdominal discomfort and pain, and diarrhea, especially when taken at doses of 15 grams or more per day. Those with lactose intolerance may experience more of these side effects. The byproducts of fermentation of FOS are hydrogen and carbon dioxide, which are the gases that can cause these uncomfortable symptoms. Adjusting the amount you ingest may alleviate some of the symptoms.

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