Inulin

Inulin is a soluble dietary fiber that occurs naturally in a number of plants. Dietary fibers are compounds that are not digested or absorbed in the human intestine. Soluble fiber attracts water and turns into gel during digestion (1). Inulin is found in over 36,000 plant species, including many that we eat every day such as wheat, onions, bananas, garlic and asparagus. It is also found in less common foods such as Jerusalem artichokes and chicory, with chicory being the main source for the commercial production of inulin (2). Chicory originally grew in Europe and Asia, but is now also grown in America. The ancient Egyptians used chicory as a medicine thousands of years ago. Plants that contain inulin use it to store energy and as protection against cold temperatures. When inulin is exposed to cold temperatures, it acts as a kind of antifreeze (3). Inulin is not absorbed by the small intestine. When it reaches the large intestine, it is fermented by bacteria. Today, inulin is being added to more and more foods due to its benefits and adaptability.

Components of inulin

Inulin consists of a chain of fructose molecules with a glucose molecule at each end. The molecules are linked together in this chain by bonds that cannot be broken by the human digestive system, which is why inulin cannot be digested by humans. Instead, the inulin molecules move slowly through the intestines, absorbing water and swelling into a gel that helps form softer stools. This makes inulin great for digestive health (4). The number of fructose molecules in each chain can vary from 2 to 60. Inulin is called high performance inulin when it has more than 10 fructose molecules in its chain. When this inulin is produced commercially, shorter chains are removed from the product. Chains containing less than 10 molecules are called fructooligosaccharides (FOS). Fructooligosaccharides have a sweet, pleasant taste and are used to enrich foods with dietary fiber (5).

Mechanisms of action

The solubility of inulin allows it to absorb a lot of water. As it swells, inulin forms a gel that absorbs fat particles and transports them out of the body (4). In addition, it increases the number of beneficial gut bacteria by acting as their food source (4).

Natural sources of inulin

Inulin is found in many foods including the following:

• Chicory root
• artichokes
• agave
• Asparagus
• bananas
• Garlic
• leek
• Wheat
• Onions
• Wild yams

Thanks to its creamy consistency, inulin is also used as a fat substitute in margarine and salad dressings. It is also used to replace part of the flour in baked goods.

Health benefits of inulin

Inulin is a prebiotic that can increase the number of "beneficial" intestinal bacteria Inulin acts as a prebiotic because it is not digestible by the human body, but serves as food for the beneficial intestinal bacteria (2, 6). Billions of beneficial bacteria live in the human gut, including bifidobacteria, which are found in the lower part of the intestine. These bacteria ferment complex carbohydrates that cannot be digested in the upper digestive tract, releasing short-chain fatty acids such as butyrate, which are essential for human health (7, 8, 9). Inulin is essentially a food for bifidobacteria and stimulates their growth and activity. Beneficial bacteria fulfill a number of important functions in the body, including the following (9, 10, 5):

• They produce acetic acid and lactic acid, which lower the pH of the intestine and prevent the growth of harmful bacteria in the gut.
• They stimulate the function of the immune system.
• They support the absorption of certain minerals.
• They increase the production of B vitamins such as folate, vitamin B12, thiamine and niacin.

Several studies have shown that inulin stimulates the growth of bifidobacteria. Eight healthy volunteers were given fructooligosaccharides instead of sucrose for 15 days and their stools were monitored. Although the total number of bacteria in their stool did not change, bifidobacteria became the predominant type (11). In another study, 10 elderly patients with constipation were given inulin for 19 days and their stools were monitored. These subjects also showed an increase in bifidobacteria with a simultaneous reduction in the number of harmful bacteria (12). Inulin therefore improves the health of the digestive tract in humans by stimulating the growth of beneficial bifidobacteria.

Some studies with bacteria grown in the laboratory show that inulin can also increase the number of some bad bacteria. These included Salmonella and bacteria such as Klebsiella and Escherichia coli (commonly known as E. coli), which do not usually cause disease in healthy people, but can cause infections in people with weakened immune systems. However, other laboratory studies show that inulin can reduce the growth of harmful bacteria such as Clostridium difficile by increasing the growth of bifidobacteria (13, 14).

Inulin reduces constipation

Due to its ability to swell after absorption of water, inulin is very effective in reducing constipation. In one study, 17 children with constipation aged 2 to 5 years were given inulin and their stool consistency was monitored. It was observed that children who were given inulin had softer stools (15). Several studies have also shown that inulin increased the frequency of bowel movements and improved stool consistency in adults (16, 17, 18). Inulin increases the bulk of the stool by forming a gel-like substance and by increasing the amount of beneficial bacteria in the human digestive tract (19).

Inulin helps to reduce appetite and prevent weight gain

When added to low-calorie foods, inulin can be an effective way to suppress appetite and control food intake (20). A study conducted with 40 women showed that consuming 16 grams of inulin in the form of fructans in the morning for a period of 7 days reduced appetite and helped to reduce food intake during lunch (21).

In another study of 125 overweight and obese adults, a snack bar containing inulin reduced hunger, appetite and food intake over the course of 12 weeks (22).

Inulin may help control appetite in several ways

• By increasing the production of the appetite-suppressing hormone peptide YY (23, 24).
• By increasing the amount of glucagon-like peptide-1 - a hormone that is released after a meal and helps to slow gastric emptying (24, 25).
• By altering neuronal activity in the brain to suppress appetite (26). These are most likely the results of increased production of short-chain free fatty acids (23, 24, 26), but there are also studies questioning their involvement (27).

Inulin could increase weight loss

In a study of 44 patients with prediabetes, those who took inulin over an 18-week period lost significantly more weight than those who took cellulose (another plant fiber) (28). Another study of 35 obese women found that inulin-rich yacon syrup reduced body weight and waist circumference (29).

Inulin could lower blood sugar levels in type 2 diabetics

In a study of 49 women with type 2 diabetes, supplementation with inulin significantly reduced fasting blood glucose (by 8.5%) and HbA1c (by 10.4%) - an indicator of average blood glucose levels over the previous three months (30).

A meta-analysis of 20 studies with a total of 607 adult participants found that there was a tendency for a reduction in blood glucose levels in type 2 diabetics (31).

Inulin reduces cholesterol levels and can improve heart health

Inulin improves heart health by reducing fat levels in the blood through several mechanisms (32):

• Inulin reduces the production of liver enzymes responsible for making fat.
• Inulin increases the amounts of enzymes that break down fat in the muscles.
• Inulin increases the production of short-chain fatty acids.
• Inulin alters the production of compounds that increase the production of peptides that promote satiety and increases the removal of cholesterol from the body in humans and rodents.

In a study of 49 women with type 2 diabetes, inulin reduced total cholesterol levels by 12.9% and triglyceride levels by 23.6% (30). A meta-analysis of 15 randomized controlled trials also concluded that dietary inulin fructans significantly reduced blood triglyceride levels (33). There also appears to be a difference in the effects of inulin in healthy subjects and patients with high cholesterol levels. Inulin reduces triglyceride levels in the blood of healthy volunteers and lowers cholesterol levels in patients with high cholesterol levels (34).

Since clogging of the arteries with cholesterol can lead to high blood pressure by making it harder for the heart to pump blood through the arteries, inulin can be used to reduce or prevent high blood pressure by lowering cholesterol levels (35).

Inulin could prevent the development of colon cancer

Rats fed a diet containing inulin had higher levels of beneficial bacteria such as bifidobacteria, while rats fed a normal diet had more harmful bacteria. Inulin prevented the occurrence of chemically induced colon cancer in these rats (36). Similar results were observed in mice (37). Furthermore, when inulin was administered in combination with beneficial microbes, it reduced the risk of colorectal cancer in rats (38, 39).

Inulin could help control inflammatory bowel disease

Studies conducted in humans and animals have shown that inflammatory bowel disease occurs because some people cannot tolerate the presence of certain gut bacteria. In such cases, prebiotics such as inulin can be used to reduce intestinal inflammation (40, 41). A study conducted with mice showed that inulin reduced the pro-inflammatory cytokine IFN-gamma while increasing levels of the anti-inflammatory IL-10. This reduced intestinal inflammation in these animals (42). However, the results of clinical trials of inulin for the treatment of Crohn's disease - another type of inflammatory bowel disease - are inconclusive (41, 43).

Inulin increases the absorption of calcium and magnesium

Two studies involving 14 women and 9 men found that supplementation with inulin increased calcium absorption and retention (44, 45). In a study of 15 postmenopausal women who were treated with either inulin or a placebo for 6 weeks, increased absorption of magnesium was observed in the inulin group (46). Inulin was also found to increase magnesium absorption and retention in rats (47, 48). One of the reasons proposed to explain this is that inulin stimulates the production of short-chain fatty acids, which reduce the pH value in the colon. This improves the solubility of #calcium and magnesium, making these minerals more available for absorption (49, 50).

Inulin could improve bone health

In a study of 98 teenagers, inulin supplementation over the course of a year increased calcium absorption and bone density compared to a control group (51). Pregnant mice given inulin had thicker bones than mice that followed a normal diet or a calcium-fortified diet. The offspring of these mice given inulin also had higher bone mineral density compared to the offspring of mice in the other groups (52).

Supplementation

Dosage forms

Inulin supplements can be found in various processed foods such as protein and cereal bars, baked goods, frozen desserts, spreads and dressings, but are also available in powder form.

The inulin used can be in the form of natural inulin (usually extracted from chicory), high performance inulin (containing only the longer chains) oligofructose (containing only the shorter chains) and fructooloigosaccharides (containing short inulin molecules made from table sugar) (5).

Dosage

In the Western world, most people consume far less fiber than the daily recommended 25 grams. The average daily consumption of inulin and oligofructose is estimated to be between 3 and 11 grams (63).

Doses of up to 10 grams of inulin per day from natural sources and up to 5 grams per day in the form of oligofructose are generally well tolerated by healthy young adults (64). A number of clinical studies have also shown that up to 20 grams of inulin and/or oligofructose per day is well tolerated and effective (63).

The best way to start taking inulin is to consume foods rich in inulin or oligofructose. If you want to supplement additional inulin, you can start with 2 to 3 grams per day for at least 1 to 2 weeks, after which you can increase the amount to 5 to 10 grams per day depending on tolerance. Based on the results of clinical studies, you can increase the amount up to 20 grams per day (63).

Can inulin be taken with natural food?

Many foods and plants contain inulin. These include asparagus, bananas, burdock, chicory, dandelion roots, garlic, artichokes, leeks and onions. Inulin is also found in some processed foods as a substitute for fat. These include chocolate bars, yogurt, cheese and ice cream. When inulin is mixed with water in a certain way, it can mimic the texture of fat in these foods.

Risks and side effects

Inulin is generally safe and harmless when used as recommended. Due to its safety, it is used to measure the filtration rate of the kidneys in humans (53). However, inulin may have certain side effects in sensitive individuals or when used in excessive amounts, including the following:

• Digestive discomfort including bloating, stomach rumbling, belching and cramping (54)
• Swelling of the intestines (55)
• Diarrhea (55)

Some users recommend starting with a low dosage (1 to 3 grams) and gradually increasing it to minimize side effects. They also report that potential digestive discomfort at the start of supplementation disappears after a few weeks of use.

Not enough is known about the effects of inulin supplementation during pregnancy and breastfeeding. However, chicory and inulin produced from chicory should be avoided by pregnant women, as chicory can lead to miscarriages. Overgrowth of bacteria in the small intestine is a condition in which there is excessive bacterial growth in the small intestine. It was previously believed that foods such as inulin, which are fermented in the digestive tract, should be avoided in this condition. Recently, however, it has been shown that prebiotics such as inulin are actually beneficial in reducing the symptoms of intestinal bacterial overgrowth, especially after antibiotic treatment (57, 58, 59, 60). In rare cases, allergic reactions may occur. In some isolated cases, inulin has led to allergic reactions that may be related to a food allergy reaction (56). Inulin can cause allergic reactions, the symptoms of which include asthma, skin rash and contact dermatitis. Inulin should be avoided if you are allergic to members of the mugwort plant family or chicory. Inulin has been observed to cause liver cancer in mice, but only in mice with an imbalance of intestinal bacteria. When administered in combination with a high-fat diet, inulin caused such an imbalance in the intestinal flora and liver cancer in mice (61).

Interactions

Chicory - and possibly chicory-derived inulin - may interact with certain medications and supplements. Inulin can also increase the amount of calcium absorbed by the body.

Limitations and precautions

Inulin is not suitable for everyone. It is rapidly fermented by bacteria in the gut. The resulting products draw water together in the intestine and release gases. This can be particularly problematic for people suffering from irritable bowel syndrome, causing bloating and a bloated feeling (55).

For people with irritable bowel syndrome, the use of low doses of inulin is recommended, as inulin can alter the intestinal flora and reduce symptoms of irritable bowel syndrome. High doses, on the other hand, have no effect on these symptoms or may even worsen them (62).

References

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Further sources

1. Raninen, K. Nutrition Reviews, January 2011.
2. Bonnema, A. Journal of the American Dietetic Association, June 2010.
3. Natural Standard Bottom Line Monograph: "Chicory (Cichorium intybus)."
4. Marteau, P. International Journal of Food Sciences and Nutrition, March 2011.
5. Charalampopoulos, D. Current Opinion in Biotechnology, April 2012.
6. Kelly, G. Alternative Medicine Review, March 2009.
7. AltCareDex: "Inulin."