What are Fructooligosaccharides?

You are likely familiar with fiber and prebiotics, and how prebiotics are good for “feeding” your probiotics or microbiota. But there are so much more to it than that.

Of all the prebiotics, fructooligosaccharides (FOS) are the primary type found in many dietary supplements. FOS is a dietary ingredient that wears a few hats – technically speaking, it is a carbohydrate but is listed as a fiber as this activity is its core strength. Another way of understanding this is that FOS are those carbohydrates that are not digested in the small intestine are subject to bacterial fermentation. And because the suffix “saccharide” means “sugar,” it is a sweet substance. As an agent for sweetness, by the way, FOS does not cause blood sugar levels to rise or spike.

Fructooligosaccharides are naturally occurring in fruits and vegetables, and are thus perfect for vegetarians and vegans. You obtain some in common produce items such as bananas, garlic, onions, artichokes and asparagus.

FOS, as with probiotics, need to reach the site within your digestive system where they can work and be effective. FOS can pass through the hydrolyzing activity of the small intestine to reach the cecum, the pouch-like area that joins the small and large intestines, where FOS become metabolized by resident microflora. Once in its preferred environment, FOS exerts a bifidogenic effect, meaning it selectively stimulates the growth of bifidobacteria residing in the colon.

How Does Fermentation Play a Role?

FOS is the perfect example of the paraphrase, “you aren’t necessarily what you eat, but what you ferment.” Your colon is a fermentation tank, the more it works this way, the healthier you are. But there is a challenge: we no longer eat enough fermented foods like our grandparents and their forebears did. Up until mass manufactured, packaged foods laden with preservatives and other additives became the staple of our diets, we used to eat a high amount of fermented foods. Homes had root cellars that existed mainly to store fruits and vegetables that were canned in jars that would naturally ferment during storage.

The upper GI primarily focuses on digesting meat (proteins) and fats, while your large intestine/lower GI acts as a fermentation tank, and this is where your gut bacteria largely reside. Part of your microbiome is composed of bacteroides, anaerobic molecules that flourish in your colon. These bacteroides ferment soluble fiber, turning it into short-chain fatty acids. When FOS from foods or dietary supplements enter the colon, they are hydrolyzed into sugars that are fermented by the bacteroides. FOS serve as the main growth factor for good bacteria residing in the gut, which then allows them to crowd out incoming pathogenic bacteria, keeping the host (you) more capable of withstanding development of conditions such as cold and flu.

Why is FOS The Best Prebiotic?

Higher intakes of dietary fiber such as FOS have long been scientifically associated with lowered risk of cardiovascular disease, supporting digestive health and weight management. Also, FOS used in foods are free of calories, offer a mild but favorable sweetness level and do not cause dental caries.

Among all the oligosaccharides that act as prebiotics, fructooligosaccharides (FOS) are one of the most researched, and shown to selectively encourage the growth of health-promoting bacteria in the gut.

One study that gave healthy participants 20.1 grams of FOS per day in three divided doses after eating showed that most of the FOS was not absorbed in the small intestine and none was excreted, which means that the FOS that reached the colon was completely fermented by the colonic bacteria.


Can FOS Help Me Lose Weight?

Yes, FOS can help with weight control. Studies show that those who consume higher amounts of fiber have lower body weight. And according to researchers of one study, overall, dietary fiber may prevent obesity by reducing body weight and even appetite control. But not all fibers exert equal action, and among the fibers this team studied, FOS affected satiety at 16 g per day for between 12 and 16 weeks. This is great news because the body needs quality fiber every day.

Another trial that gave obese participants FOS-enriched cookies found that the 9 g FOS increased satiety. And in one study that sought to link FOS consumption and satiety, researchers suggested that FOS’s satiety effects may be caused by colonic fermentation. They found that FOS is fermented in the colon within 240 minutes after consumption.

Other Benefits of FOS


Consuming FOS regularly will give you other health benefits, as some studies have shown. For example, did you know that FOS can help promote better cognitive function? First, researchers gave FOS and other prebiotic fibers to rats for 5 weeks. They showed increased activity of neurochemical receptors important in learning and memory.

In elderly individuals with frailty syndrome, a prebiotic formula containing FOS was shown in a placebo-controlle,d randomized, double-blind study to provide improvements in two criteria – exhaustion and hand-grip strength. The researchers concluded that therapeutic approaches that impact the gut microbiota-muscle-brain axis may be useful in these cases. In relatively healthy individuals, this study suggests that FOS and inulin can help provide energy.

FOS may also favorably impact cholesterol profiles, especially in those individuals who are actively following a healthy lifestyle. Researchers who performed a meta-analysis found that FOS consumption may have a beneficial effect on lipid metabolism and regulation of serum cholesterol levels in people who change their lifestyle. The scientists concluded that FOS supplementation may be a viable strategy for lowering cholesterol.

Where Can I Get FOS?

There are some foods that have good levels of FOS. You just have to ensure that you eat them every day and enough of them to obtain the fructooligosaccharide amount your gut needs.



This South American tuber is considered the best source of FOS. One scientific review of yacon highlighted studies showing that its FOS content can reduce glycemic index, body weight and the risk of colon cancer. The review discussed how yacon’s FOS content positively affects the intestinal microbiota, increase glucose absorption, stimulate insulin secretion in the pancreas and influence cholesterol profile. The scientists concluded that based on the studies they evaluated, yacon roots may be effectively used as a dietary supplement to support overall health.

Jerusalem Artichoke


Jerusalem artichoke is also a tuber; it is very similar to the potato and is a great source of FOS and other good carbohydrates. One study that gave Jerusalem artichoke to rats showed significant improvement in expression of specific genes associated with blood sugar insufficiency, diabetes type 2 and non-alcoholic fatty liver disease. The researchers asserted that Jerusalem artichoke may be a viable supplement to support against the risk of development of these conditions.

Dietary Supplements


FOS as part of a dietary supplement that also provides probiotics, such as L. paracasei, taken daily can dramatically bolster your well-being in many ways, especially after several months. You will notice your gut feeling calmer, among other signs of general health.

Why Are Fermented Foods Good?

As discussed, in modern society, we do not eat anywhere as near the amount of fermented foods as our ancestors. But they are widely available and tasty; also many are low in calories. Although they don’t contain FOS, some fermented foods (below) contain beneficial bacteria, which is needed to replenish your own colonies that feed and grow from FOS.



Yogurt is perhaps the most popular fermented food. However, as more types are launched into an already crowded marketplace due to continued surging demand, you want to stay away from those that are more like desserts, with added sugars and “crunchies.” Non-fat or low-fat plain yogurt is your best bet; blend it with fresh fruit and enjoy the benefit of added antioxidants.



Similar to yogurt is a fermented beverage kefir, which is a liquid (consistency of a milkshake). Drinking kefir, according to some studies, may decrease intestinal inflammation, reducing the amount of toxins entering the bloodstream. A similar caution here, read the labels to ensure there isn’t added sugars.




Fermented cabbage is a very good source of friendly bacteria; but make sure that the type you buy is not heat-treated (which destroys the probiotics). Its sour taste is due to the probiotics’ breakdown of lactose (lacto-fermentation).




This is a beverage that is now widely available in supermarkets as a cold, fizzy beverage. It is made from tea, and other ingredients, and research shows it protects the digestive tract against several pathogenic bacteria, as well as supports smooth, calm digestion.




As many devotees will tell you, pickles are the best fermented food ever, in chips, slices or whole. They are said to support immune function and assist in digestion.

As you can see, fructooligosaccharides (FOS) are a versatile prebiotic that can benefit your body in many ways. Add some healthy fermented foods to your daily diet, and see how much better you will feel!

What are the Benefits of Herbal Teas?
What are the Benefits of Pea Protein?
What’s New in Microbiota Research?