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What is Fructooligosaccharide? Understanding the Benefits and Uses

Fructooligosaccharides (FOS) are oligosaccharides, a form of carbohydrate, made up of short chains of fructose molecules. Occurring naturally in various plants, such as onions, garlic, blue agave, bananas, and artichokes, FOS contributes to their sweetness. Their chemical structure involves linear chains of fructose units, linked by beta (2-1) bonds, with the number of fructose units ranging from 2 to 60 and often terminating in a glucose unit.

FOS are not only present in the natural sources mentioned above but are also used as an alternative sweetener in commercial applications. Exhibiting sweetness levels between 30 and 50 percent of sugar in commercially prepared syrups, they offer potential health benefits, as they act as a prebiotic, nourishing the beneficial bacteria in our guts. However, potential risks and side effects, such as extreme consumption, should be considered.

Key Takeaways

  • Fructooligosaccharides are carbohydrates composed of short fructose chains found in various plants.
  • Often used as an alternative sweetener, FOS have potential health benefits as a prebiotic.
  • It’s essential to consider potential side effects and safety concerns related to FOS consumption.

Formation and Structure

Fructose, Sucrose, and FOS

Fructooligosaccharides (FOS) are a type of carbohydrate composed of short fructose chains. These FOS molecules occur naturally in various plants, such as blue agave and yacon. The main monomeric unit of this oligosaccharide is fructose, with a terminal glucose unit attached. The structure contains repetitions of inulobiose, levanobiose, and sucrose. FOS exhibits sweetness levels between 30 and 50 percent of sugar in commercially prepared syrups.

Fructose, a simple sugar, is one of the building blocks of FOS. It can be found naturally in many fruits, honey, and some vegetables. Sucrose, another simple sugar, consists of one glucose molecule and one fructose molecule joined together. Sucrose is commonly known as table sugar and can be found in sugar cane and sugar beet.

Polymerization and Glycosidic Bonds

FOS are formed through the polymerization process, which involves creating glycosidic bonds between fructose units. Specifically, FOS molecules possess β (2 → 1) fructosyl-fructose glycosidic bonds. This type of bond means that it cannot be processed by the digestive enzymes in the mammalian digestive system, making FOS indigestible.

In the FOS structure, there are several molecules worth mentioning:

  • Kestose: This trisaccharide is composed of one glucose molecule and two fructose molecules. It is the smallest FOS type.
  • Nystose: This tetrasaccharide is made up of one glucose molecule and three fructose molecules. It is a larger FOS variety.

To summarize, fructooligosaccharides are carbohydrates composed of short fructose chains, formed through polymerization and glycosidic bonds, and can be found naturally in numerous plant sources. The structure of FOS contains repetitions of various molecules such as inulobiose, levanobiose, and sucrose, and includes specific FOS types such as kestose and nystose.

Sources and Types

Fructooligosaccharides (FOS) are a type of carbohydrate composed of short fructose chains called oligosaccharides. They are naturally occurring in various plants and can also be extracted or synthesized as additives. This section focuses on the natural sources, extracts, and additives of FOS.

Natural Sources

FOS can be found in a range of plant-based foods, including:

  • Garlic: Both a flavorful ingredient and a healthy source of FOS.
  • Onion: Contains FOS and adds a distinct taste to many dishes.
  • Chicory root: A popular source of FOS and inulin, often used as a coffee substitute.
  • Asparagus: Provides a good amount of FOS and is a delicious vegetable with various culinary uses.
  • Artichoke: Both globe artichoke and Jerusalem artichoke contain FOS, with the latter being a particularly rich source.
  • Leeks: A close relative of onions and garlic, leeks also provide FOS.
  • Banana: While not as concentrated in FOS as other sources, bananas provide a small amount of this beneficial carbohydrate.


Some processed extracts that are rich in FOS include:

  • Inulin: Derived mainly from chicory root, inulin is a soluble fiber and a popular source of FOS, often used in food products as a prebiotic and dietary fiber supplement.
  • Blue agave syrup: This natural sweetener, obtained from the blue agave plant, contains FOS as a major component.


In commercially prepared products, FOS can be used as an alternative sweetener. These additives are obtained by extracting and synthesizing FOS from various sources. They provide sweetness levels ranging from 30% to 50% of traditional sugar. An example of a FOS-based additive is:

  • Oligofructose: A synthesized form of FOS that is used as a sugar substitute in various food products, providing a lower-calorie alternative to traditional sweeteners.

In summary, fructooligosaccharides are naturally occurring in a variety of plant-based foods and can also be found in the form of extracts and additives. They provide numerous health benefits, such as promoting gut health, and may act as alternative sweeteners in some products.

Health Benefits

Prebiotics and Gut Microbiota

Fructooligosaccharides (FOS) have been known to act as prebiotics, providing health benefits by promoting the growth of beneficial bacteria in the gut. FOS are non-digestible carbohydrates that serve as a food source for probiotics, such as bifidobacteria and lactobacilli. In turn, these probiotics improve digestion, boost the immune system, and reduce inflammation in the gut.

Cholesterol and Blood Sugar Regulation

FOS consumption is believed to have a positive effect on cholesterol and blood sugar levels. Research has shown that FOS may decrease the levels of serum cholesterol, triacylglycerols, and phospholipids. This helps maintain a healthy cardiovascular system. In addition, FOS intake has been associated with better glucose regulation, which is essential for individuals with diabetes or those at risk of developing the condition.

Bone Health and Mineral Absorption

FOS can enhance the absorption of minerals like calcium and magnesium, which are crucial for maintaining strong and healthy bones. Improved calcium absorption helps reduce the risk of osteoporosis, a condition characterized by weak and fragile bones. Furthermore, magnesium plays a vital role in bone health and general wellbeing, making FOS helpful for overall health.

Potential Side Effects and Safety

Digestive Discomfort

Fructooligosaccharides (FOS) are a type of carbohydrate composed of short fructose chains and naturally occur in fruits and vegetables. As a sweetener, they can cause digestive discomfort in some individuals. Common side effects include:

  • Gas
  • Bloating
  • Diarrhea
  • Nausea
  • Cramps

These side effects may be more noticeable in people with sensitivity to FOS or those consuming large amounts.

Allergic Reactions and Interactions

Although rare, some individuals may experience allergic reactions to FOS. Symptoms of an allergic reaction may include:

  • Hives
  • Swelling of the face, lips, or tongue
  • Difficulty breathing
  • Rapid or irregular heartbeat

If you experience any of these symptoms, discontinue use and seek immediate medical attention.

As for interactions, there is limited information available about any contraindications between FOS and medications. However, it’s important to consult your healthcare provider before adding any new supplements to your regimen, especially if you are taking prescription medications.

Pregnancy and Infant Formula

There is not enough reliable information on the safety of FOS during pregnancy or breastfeeding. Although it is found naturally in some fruits and vegetables, it’s best to consult your healthcare provider before consuming large amounts of FOS during pregnancy.

The use of FOS in infant formula and baby formula is relatively more common, as it is believed to promote healthy gut bacteria in infants. However, the safety and efficacy of FOS usage in infant formulas are still topics of ongoing research.

Dietary Applications and Alternatives

Alternative Sweeteners

Fructooligosaccharides (FOS) are subtly sweet, low-calorie alternative sweeteners that can be used in place of sugar. They are nondigestible, meaning they don’t affect blood sugar levels, making them suitable for diabetics. FOS are naturally found in plants, such as onions, chicory, garlic, asparagus, bananas, and artichoke among others.

Food Industry Uses

In the food industry, FOS are used in various products due to their soluble nature and ability to provide dietary fiber. They are commonly found in yogurt, where they help promote the growth of beneficial bifidobacteria. Since FOS are derived from natural sources like cane sugar and seaweed, they are considered a healthier alternative compared to artificial sweeteners.

Weight Management and Obesity

Fructooligosaccharides can play a role in weight management and obesity prevention due to their low-calorie content. As they are nondigestible, FOS might help reduce overall calorie intake without contributing significantly to weight gain. Additionally, they exhibit prebiotic properties that support healthy gut bacteria, which can potentially aid in digestion and alleviate constipation. However, more research is needed to fully understand the relationship between FOS and body weight regulation.

Research and Future Implications

Cancer and Degenerative Diseases

Fructooligosaccharides (FOS) have been studied for their potential role in preventing chronic diseases like cancer and degenerative diseases. The biomedical research suggests that FOS may have a positive impact on gut health, which in turn could lead to a systemic response that improves overall health. Through the modulation of inflammatory, oxidative, and immune activity in the gut, FOS might contribute to a lower risk of developing these diseases1.

Irritable Bowel Syndrome and Digestive Health

Irritable Bowel Syndrome (IBS) and other digestive disorders may benefit from FOS supplementation, as they promote the growth of good bacteria like Lactobacillus in the intestinal microflora2. By supporting a healthy balance of gut bacteria, FOS can aid in digestion and the absorption of nutrients, potentially alleviating some IBS symptoms. Additionally, FOS are nondigestible and do not affect blood sugar levels or insulin secretion3, making them suitable for diabetic individuals.

Microbial Ecology and Fermentation

FOS play a crucial role in the microbial ecology of the gut, as they can serve as a substrate for fermentation4. This process generates short-chain fatty acids (SCFAs), which are important energy sources for the cells lining the colon and contribute to maintaining gut health. By promoting the growth of beneficial bacteria like Lactobacillus and inhibiting the growth of harmful bacteria such as E. coli, FOS may further enhance gut health and support a healthy digestive system5.

Frequently Asked Questions

How do fructooligosaccharides function as a prebiotic?

Fructooligosaccharides (FOS) act as a prebiotic by providing a food source for beneficial bacteria in the gut. These microbes ferment FOS, and in doing so, produce short-chain fatty acids and other metabolic by-products. This process helps create a healthy gut environment, which supports digestion, immune function, and overall health.

What are the health benefits of fructooligosaccharides?

Fructooligosaccharides provide several health benefits, which include:

  • Promoting the growth of beneficial gut bacteria, leading to improved digestion and nutrient absorption
  • Enhancing immune function through maintaining a healthy gut environment
  • Potentially reducing the risk of certain diseases, such as obesity and type 2 diabetes, by moderating blood sugar levels
  • Contributing to better bone health by increasing calcium absorption

What is the chemical structure of fructooligosaccharides?

Fructooligosaccharides are composed of short chains of fructose molecules connected by β-2,1-glycosidic linkages. They are classified as a type of carbohydrate called oligosaccharides. Depending on the number of fructose units, FOS can be classified into different types, such as 1-kestose, nystose, and fructosylnystose.

How many calories are in fructooligosaccharides?

Fructooligosaccharides have a lower caloric content compared to regular sugar. They provide about 1.5 to 2 calories per gram, whereas sugar contains 4 calories per gram. This makes FOS a favorable alternative sweetener for those looking to reduce caloric intake.

What is the glycemic index of fructooligosaccharides?

The glycemic index (GI) of fructooligosaccharides is much lower than that of regular sugar, as they have a minimal impact on blood sugar levels. FOS have a GI value of less than 20, whereas regular sugar has a GI value of around 65. This low GI may contribute to their potential benefits for blood sugar management and diabetes risk reduction.

Are fructooligosaccharides safe for dogs?

Fructooligosaccharides are generally considered safe for dogs in small amounts, as they can have similar prebiotic effects on dogs’ gut health as they do in humans. However, excessive consumption may cause digestive issues such as gas, bloating, or diarrhea. Consult your veterinarian for guidance on incorporating FOS into your dog’s diet.


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  2. “Fructooligosaccharides: Effects, Mechanisms, and Applications”

  3. “Fructooligosaccharides: Benefits and Risks – Healthline”

  4. “Status and Future Prospects of Fructooligosaccharides as Nutraceuticals …”

  5. “Dietary fructooligosaccharides and potential benefits on health”