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Fructo-oligosaccharides (FOS) or Oligofructose

What are fructooligosaccharides (FOS)?

Fructooligosaccharides (FOS) or oligofructose are indigestible carbohydrates made mainly of fructose ^[1]. They are soluble fiber.

Nutrition Facts

FOS is not digested in the small intestine, so it passes to the large intestine, where it is broken down (fermented) by beneficial large intestinal bacteria into gases, like hydrogen, and short-chain fatty acids (SCFAs), which are absorbed and can provide 1.5-2.7 kilocalories per gram ^[1,2,3]. FOS is mainly used as a sweeteners–it is 30-50% as sweet as sucrose–, taste enhancers or as “added fiber” ^[4]. On the Nutrition Facts labels, FOS is included in the total carbohydrates under “dietary fiber.”

FOS Structure

FOS is made of fructose molecules with one glucose molecule on the end, altogether of less than 10 simple sugars ^[1].

Short-Chain FOS or scFOS

Short-chain FOS is defined as unbranched chains made of ≤9 fructose molecules ^[17].

Picture 1. Examples of foods high in fructooligosaccharides

List of Foods Containing FOS

FOS or oligofructose occurs naturally in significant amounts in ^[6,7]:

Jerusalem artichokes (up to 6 g/100 g)
Shallots (up to 5 g/100 g)
Red onions (up to 2,5 g/100 g) ^[6,7]

Examples of other foods containing smaller amounts of FOS: asparagus, ripe bananas, brown sugar, chicory roots, dahlia, endive, garlic, leeks, onions, murnong (Australian tuberous plant), yacon (Peruean tuberous plant) ^[5].

FOS can be added as a sugar substitute to “low-calorie foods,” or as a bulking agent or “added fiber” to nutritional bars and beverages, baby foods, biscuits, cakes, confectionery, milk, hard candies, ice cream, yogurt, jams, jellies, muffins, ready-to-eat cereals, sorbet, pre-prepared soups or other commercial foods ^[5].

FOS Supplements

FOS can be extracted from chicory roots or produced from inulin (using the enzyme inulase) or sucrose (using the enzymes derived from Aspergillus japonicus yeasts) ^[5]. FOS is available as powder or capsules. It can be found in some prebiotic, probiotic and fiber supplements. Before buying FOS-containing supplements, consider there are plenty of natural foods containing prebiotics and fiber.

Insufficient Evidence About FOS Health Benefits

Irritable bowel syndrome. FOS does not improve symptoms of IBS; it can even worsen them ^[11].

Constipation. In one study, FOS did not speed up the passage of food through the gut or increased the stool weight ^[9]. In some other studies FOS increased the frequency of bowel movements, but since FOS may produce quite some gas, it does not seem to be a suitable remedy to prevent constipation.

Crohn’s disease. In one study, FOS decreased activity of Crohn’s disease but more research is warranted ^[10,^16].

Diabetes mellitus. In 2 studies, consumption of FOS in doses 15-20 g/day for 20 days to 4 weeks did not affect glucose and cholesterol levels in individuals with diabetes type 2 ^[19,20].

Cholesterol levels. There is insufficient evidence about the effect of FOS on blood LDL cholesterol or triglyceride levels ^[9,12].

Calcium and magnesium levels. In some, but not all, studies FOS increased absorption of calcium and magnesium ^{[5,21,22,23,24]}, but it is not clear if this has any beneficial effect for humans.

Weight loss. In one small study, overweight individuals, after consuming oligofructose in the dose 21 g/day for 12 weeks, had increased feeling of satiety and lost 0.4-1 kg of body weight in average ^[16].

FOS in infant formula. According to The European Scientific Panel on Dietetic Products, there is no evidence that adding FOS to infant formula would have any benefits for infants ^[15].

FOS Is a Prebiotic

FOS is a prebiotic – it promotes the growth of beneficial intestinal bacteria (Bifidobacteria and Lactobacilli) in the large intestine ^[5,9,25]. The actual benefit of prebiotics for humans is not yet well known, though.

Safety: Risks, Dangers

FOS is considered a novel food – food that does not have a long-term history of safe use ^[14]. Acceptable Intake Level for FOS for individuals older than one year is 20 g/day, and for infants 4,2 g/day ^[5]. Within the mentioned intake levels, FOS is Generally Recognized As Safe (GRAS) by the US Food and Drug Administration (FDA) ^[5]. FOS does not significantly increase blood sugar and insulin levels ^[5].

FOS can promote dental caries to about the same extent as sucrose ^[13].

During Pregnancy

Do not take FOS supplements during pregnancy or breastfeeding because not enough research has been made to prove their safety during these periods ^[18].

FOS Side Effects

FOS, when consumed in amounts exceeding 20 g/day by healthy people, may cause abdominal bloating, pain or cramps, excessive gas (flatulence), loose stools or diarrhea ^[5].

FOS Intolerance

FOS is fermentable by intestinal bacteria, so it belong to FODMAPs (Fermentable, Oligo-, Di- and Monosaccharides and Polyols), which can, even in small amounts, trigger excessive gas and diarrhea in sensitive individuals, mainly in those with fructose malabsorption and irritable bowel syndrome (IBS).

FOS and Cooking

FOS is commercially available as FOS syrup or powder ^[5]. Properties:

30-50% as sweet as sucrose ^[4]
More soluble in water than sucrose; it does not crystallize ^[8-p.386]
Can undergo the Maillard browning reaction during cooking ^[8-p.386]

Frequently Asked Questions

1. Is FOS vegan?

Artificially produced FOS is made from inulin by the help of yeasts, so they are not vegan.

2. Does FOS contain gluten?

FOS can be derived from wheat but should be gluten-free.

3. Why is FOS added to probiotic supplements?

FOS promotes the growth of probiotic bacteria.

4. Is FOS fructan?

Yes, FOS belong to fructans, which are oligo- or polysaccharides that contain at least 3 simple sugars, from which the main one is fructose.

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