Prebiotics, Inulin, and FOS: Health Benefits and Concerns
Inulin, FOS, and Intestinal Bacteria
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 pass through the small intestine without being digested and absorbed. Prebiotics are food chemicals that provide nutrition for some of the intestinal bacteria. The term is often restricted to nondigestible fibre, which includes inulin and FOS.
Inulin and FOS 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.
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 fructans, which are long molecules made of fructose units. Fructans 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 have longer chains that generally consist of ten to sixty fructose molecules.
The words fructooligosaccharide and inulin are often used in the singular, 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.
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 intestine. 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.
Jerusalem Artichokes or Sunchokes: Rich in Inulin
"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 or 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. 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.
How to Cook Jerusalem Artichokes
Dietary Benefits of Inulin and Fructooligosaccharide
Fructans are considered to be a type of dietary fibre, 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. However, 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 thought 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 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.
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 in 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 in people is needed.
One analysis of clinical trials in humans found that inulin lowered the triglyceride and cholesterol level in the blood of people with high amounts amounts of these chemicals but not in people with normal amounts.
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, flatuence, 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 in 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. There doesn't seem to be any scientific evidence that prebiotics increase the number of bad 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 will vary from individual to individual.
Fructans in a Healthy Diet
The foods that contain inulin and FOS are healthy foods for many reasons. Nutritionists highly 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. Taking concentrated inulin or FOS in supplements is a special situation and should be discussed with a doctor.
- Slavin J. Fiber and Prebiotics: Mechanisms and Health Benefits. Nutrients . 2013;5(4):1417-1435. doi:10.3390/nu5041417.
- Faux fiber versus the real thing from Berkeley Wellness, University of California
- Effect of agave fructans on mineral absorption and bone health in mice from the NIH (National Institutes of Health)
- Inulin-type fructans and the lipid profile from the NIH
- Effects of inulin on the plasma lipid profile from Medscape
- Fructans modulate the immune system in mice from Frontiers in Immunology/PubMed
- Oligofructose ingestion and weight in rats from the CBC (Canadian Broadcasting Corporation)
Questions & Answers
© 2013 Linda Crampton