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Fructans, FOS, Inulin, and Prebiotics: Benefits and Concerns

Linda Crampton is an experienced teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

The root of Cichorium intybus or the common chicory is a great source of inulin.

The root of Cichorium intybus or the common chicory is a great source of inulin.

What Are Fructans?

Our large intestine is home to a huge bacteria population. Most of the bacteria seem to be friendly organisms that help us in some way. They feed on components of food that reach the small intestine. Prebiotics are food chemicals that provide nutrition for some intestinal bacteria. The term is often restricted to non-digestible fiber, which includes FOS and inulin.

FOS and inulin are types of fructans. FOS is also known as fructooligosaccharide or oligofructose. We can't digest fructans, but some of our intestinal bacteria can break them down in a process known as fermentation. Fructans are thought to have important health benefits for humans. They also have properties that make them useful as food additives. They may cause digestive problems in some people, though.

Monosaccharides are single sugar molecules, such as glucose, fructose, and galactose. (The word "sugar" has a different meaning in science than it does in everyday life.) Monosaccharides exist on their own or join together to make new substances.

What Are Fructooligosaccharides and Inulins?

Fructooligosaccharides and inulins are long molecules made of fructose units. They are obtained from plants or produced by food chemists in laboratories.

  • Fructose is a monosaccharide and is the main type of sugar in fruit.
  • Fructooligosaccharides are fructans with a short chain length (generally two to nine fructose molecules).
  • Inulins are fructans that have longer chains and generally consist of ten to sixty fructose molecules.

The words fructooligosaccharide and inulin are often used in the singular— especially in the case of inulin—but each substance actually consists of a range of chemicals with different lengths. The borderline between FOS and inulin classification based on chain length is somewhat variable. In addition, natural inulin often contains a mixture of both short and long chain fructans.

Fructans are made by certain bacteria as well as by plants. The fructans made by bacteria are much longer than plant fructans and are known as levans. A single levan molecule may contain hundreds of thousands of fructose molecules.

In the case of plant fructans, molecules of FOS tend to have shorter chains than those of inulin (though the variability mentioned above should be noted). I use the fact that FOS comes before inulin alphabetically to remember the difference.

Natural sauerkraut is a good source of probiotics.

Natural sauerkraut is a good source of probiotics.

Difference Between Prebiotics and Probiotics

Although their names sound very similar, prebiotics and probiotics are different from one another. Some researchers feel that we need both in order to be healthy.

  • Prebiotics are nutrients found in food that nourish the good bacteria in our intestines. FOS and inulin are examples of prebiotics.
  • Probiotics are good bacteria that can potentially survive in our large intestine and help us in some way. They're found in foods such as yogurt and natural, refrigerated sauerkraut.

Probiotic bacteria may boost the activity of the immune system, improve the condition of the intestinal lining, reduce intestinal inflammation, and improve digestive health.

"Inulin" shouldn't be confused with "insulin," which has a completely different structure and function. Inulin is a carbohydrate made by plants. Insulin is a protein made by our pancreas that helps glucose (blood sugar) leave our blood and enter our cells. The cells break the glucose down to produce energy.

Inulin and FOS in Food

Inulin occurs naturally in many plants, especially onion, garlic, chicory root, Jerusalem artichokes (also known as sunchokes), and the blue agave plant. There are also significant amounts in leeks, dandelion root, burdock, bananas, and asparagus. FOS is found in many plants, too, because they can easily convert inulin into shorter fructans.

In the food industry, inulin is often obtained from the roots of the common chicory plant, which belongs to the dandelion family, or the Asteraceae. The inulin can be broken down in a lab to make FOS. Inulin can also be made artificially from sucrose (table sugar) molecules. A sucrose molecule consists of a glucose molecule joined to a fructose molecule.

Dietary Benefits of Fructans

Fructans are considered to be a type of dietary fiber since they are long molecules that we can't digest. The food industry loves plant-type fructans for a variety of reasons.

Shorter fructans have a sweet taste but don't contribute calories to our body because we can't digest them. They are sometimes used as sweeteners for food. They are safe for diabetics and don't cause cavities.

Longer fructans are either not sweet or only mildly sweet. They give food the texture and mouthfeel that are usually supplied by fat, thereby reducing or eliminating the need for added fat in the food.

Prebiotic Benefits of Fructans

Although our bodies can use fructose as an energy source, we can't use fructans for energy. Fructan molecules are too large to be absorbed through the lining of the small intestine, where the rest of our food is absorbed. In addition, we lack enzymes that can break the bonds joining the fructose molecules together in fructans, so we can't digest them into smaller pieces.

Some of the bacteria living in our large intestine can break down fructans, however. Inulin and fructooligosaccharides appear to promote the growth of friendly intestinal bacteria by providing them with food. They seem to have their strongest effect on bacteria belonging to the bifidobacteria group.

The blue agave plant is a good source of inulin. The plant is also used to make tequila.

The blue agave plant is a good source of inulin. The plant is also used to make tequila.

Other Possible Health Benefits of Fructans

Research suggests that inulin and/or FOS have additional health benefits. These may be produced by the increased population of friendly bacteria, or they may arise due to a different reason. Some of the research into the benefits of inulin and FOS has been done on rodents. The results may apply to humans as well, but this isn't necessarily true.

  • Fructans may lower the level of triglycerides, or fats (a type of lipid), in the blood. Having a high blood triglyceride level increases the risk of heart disease.
  • Fructans relieve constipation by increasing the volume of stool.
  • They may increase the absorption of minerals such as calcium and magnesium from the intestine.
  • In addition, they may modulate the activity of the immune system in the intestine, thereby helping people with inflammatory bowel disease. Modulation is a process in which the overactivity or underactivity of the immune system is corrected.
  • Research in rats indicates that oligofructose is useful in weight loss. One research project found that oligofructose also causes weight loss in humans, but more research on people is needed to confirm this.

One analysis of clinical trials in humans found that inulin lowered the triglyceride and cholesterol levels in the blood of people with high amounts of these chemicals but not in people with normal amounts.

Garlic is another good source of inulin.

Garlic is another good source of inulin.

Fructan and Prebiotic Concerns

The amount of inulin and FOS that the large intestine can tolerate is limited. Bacteria break down fructans by the process of fermentation, which produces gas. If too much gas is produced, a person may experience bloating, flatulence, and diarrhea. The seriousness of the problem depends on the type and amount of fructan that's been ingested, the types of bacteria living in the large intestine, and the ability of the person's intestine to absorb excess gas.

The tendency of fructans to cause diarrhea might actually be an advantage for people who are suffering from constipation. They've been used to help elderly people with this problem, for example. Although inulin and FOS are considered to be safe in normal food amounts, anyone considering taking them in a supplement form should check with their doctor first.

Prebiotics support the growth of good bacteria, but it's been suggested that they might provide food for bad bacteria, too. At the moment, there doesn't seem to be any scientific evidence that prebiotics increase the number of harmful bacteria, however. Research suggests that prebiotics such as fructans have health advantages and not disadvantages, except for their ability to produce digestive upset if eaten in excess. The "excess" amount varies from individual to individual.

The root of the greater burdock contains inulin.

The root of the greater burdock contains inulin.

Inulin and FOS in a Healthy Diet

The foods that contain inulin and FOS are healthy foods for many reasons. Nutritionists recommend that we eat whole, unprocessed foods that come from a wide variety of plants. In this way, we'll obtain not only the fructans but also the many other nutrients that are present in the plants.

"Functional" foods are those that have had a substance added to them to provide health benefits. Some functional foods contain added inulin or FOS. It will be interesting to discover whether ingesting these foods offers any advantages to eating lots of foods that are naturally high in fructans.

Ingesting concentrated inulin or FOS in enriched food or supplements is a special situation and should be discussed with a doctor. Eating a varied and nutritious diet that includes some fructans seems like a good idea for everyone, except perhaps for people who have a fructan intolerance.


  • Fiber and Prebiotics: Mechanisms and Health Benefits from the "Nutrients" journal and MDPI
  • Effect of agave fructans on mineral absorption and bone health in mice from the NIH (National Institutes of Health) : Abstract
  • Inulin-type fructans and the lipid profile from the NIH (Abstract)
  • Effects of inulin on the plasma lipid profile from Medscape (Abstract)
  • Fructans modulate the immune system in mice from Frontiers in Immunology/PubMed
  • Oligofructose ingestion and weight in rats from the CBC (Canadian Broadcasting Corporation)

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2013 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on July 07, 2016:

Thank you for the visit, Kim. I'm glad that the article was helpful for you!

Kim Maravich from Pennsylvania on July 07, 2016:

I'm late to this hub, but I wanted to thank you for your information. I was reading about inulin recently, and your information helped me to understand it better. I also appreciate the video on cooking Jerusalem artichokes!

Linda Crampton (author) from British Columbia, Canada on July 25, 2013:

Thank you so much for the lovely comment, Helen! I appreciate it very much. Thank you for the vote, too.

Helen Murphy Howell from Fife, Scotland on July 25, 2013:

Excellent hub and packed full of information. What I loved about your hubs, is not only their interest factor, but you handle difficult subjects so well you put it across so that everyone can understand the issues at hand. This is not an easy thing to do, so I really take my hat off to you for this wonderful talent you have!

Fascinating hub + voted up!

Linda Crampton (author) from British Columbia, Canada on July 23, 2013:

Thank you, Martie. I appreciate your visit and comment a great deal!

Martie Coetser from South Africa on July 23, 2013:

Awe-inspiring interesting! Alicia, I always learn so much in your hubs. Finally I have a clue why garlic turns my stomach upside down, not to talk about the gas caused by onions, cabbage, etc. Brilliant!

Linda Crampton (author) from British Columbia, Canada on July 22, 2013:

Thanks for the comment and the vote, Eddy. I hope you enjoy your day, too!

Eiddwen from Wales on July 22, 2013:

Oh so very interesting Alicia ;voted up and enjoy your day.


Linda Crampton (author) from British Columbia, Canada on July 21, 2013:

Hi, Deb. Yes, I agree - unless someone has a specific health problem that requires a supplement as a medical treatment, unprocessed foods are the best way to obtain nutrients. Thanks for the comment!

Deb Hirt from Stillwater, OK on July 21, 2013:

Great info! Foods in their natural form, and especially unprocessed is surely best. Thanks once again for the health talk!

Linda Crampton (author) from British Columbia, Canada on July 20, 2013:

Hi, drbj. Thanks for the visit and the comment. Yes, there are so many interesting things that we could learn and so little time available!

drbj and sherry from south Florida on July 20, 2013:

Prebiotics and probiotics. So much good information, Alicia, and so little time. Thanks for your excellent research and explanations.

Linda Crampton (author) from British Columbia, Canada on July 20, 2013:

Thank you very much for the comment and the vote, Gail.

Gail Meyers from Johnson County, Kansas on July 20, 2013:

This is very well written and informative hub, Alicia. I did not know which foods contained FOS. Thanks for the information. Voted up.

Linda Crampton (author) from British Columbia, Canada on July 19, 2013:

Thank you very much for the kind comment, Faith Reaper. I appreciate the share and the hugs as well!

Faith Reaper from southern USA on July 19, 2013:

What a wealth of great information here. Thanks for explaining the difference between the prebiotics and the probiotics, as my sister's doctor has her taking one or the other, so I will share this great information here. It is obvious you care a lot about these types of health issues and thank you for sharing your knowledge with us all.

Vote dup ++++ and sharing


Faith Reaper

Linda Crampton (author) from British Columbia, Canada on July 19, 2013:

Thank you very much for the comment, Pamela. Thanks for the vote and the share as well! I appreciate your visit.

Pamela Oglesby from Sunny Florida on July 19, 2013:

This is really a very interesting hub and you explained everything so well. I learned several things from this hub. Voted up and shared.

Linda Crampton (author) from British Columbia, Canada on July 19, 2013:

Bill, thank you so much for the lovely comment! I find biology fascinating and love trying to help other people understand and appreciate it. I would change my HubPages user name if I could. It seems rude to tell people that I'm really Linda, not Alicia, when they're "talking" to me on HubPages! I chose my pen name when I was still new to online writing and hadn't thought about my online identity carefully. Thanks for the vote, the share and the pin - as always, I appreciate them all. I hope you have a great weekend, too.

Bill De Giulio from Massachusetts on July 19, 2013:

Hi Alicia. Okay, clarify something for me. I know you have a degree in biology and teach high school, but are sure you're not a doctor. Your knowledge on topics that seem so complicated and confusing is amazing. You have an uncanny ability to put these topics into terms that even I can understand. I always learn so much from your hubs.

Hey, on another unrelated topic, I just noticed that your name is Linda, yet we all refer to you by your pen-name here, Alicia. I can't believe that I hadn't noticed this before. Anyway, great job. Voted up, shared, pinned, etc. Have a great weekend.

Linda Crampton (author) from British Columbia, Canada on July 19, 2013:

Thank you very much, pinto2011. I appreciate your comment!

Subhas from New Delhi, India on July 18, 2013:

Hi Alicia! These are very resourceful and helpful study of these three ingredients.

Linda Crampton (author) from British Columbia, Canada on July 18, 2013:

Hi, Sue. Yes, some people haven't heard about prebiotics, or they get the word confused with probiotics! Thank you very much for the vote, the share and the pin.

Susan Bailey from South Yorkshire, UK on July 18, 2013:

I was talking about prebiotics the other week to my daughter and wondering if I should buy some. I've known about inulin for years but never heard of fructans. My daughter told me that I meant probiotics not prebiotics. She hadn't heard of them. One up for mum! Voted up and pinned and shared.

Linda Crampton (author) from British Columbia, Canada on July 18, 2013:

Thanks for the comment, Bill. I'm always amazed by your visits so soon after I publish a hub! Thank you very much for the support.

Bill Holland from Olympia, WA on July 18, 2013:

Very helpful information, Alicia. I'm always a bit amazed that you can take complicated subject matter and make it so easy to understand. Thank you for this.