Fructan — Intolerance, Food Sources, Health Benefits, & More

by Arpi Gasparyan | Last updated on August 09, 2024

Medically reviewed by Elen Khachatrian

fructan health benefits, food sources and intolerance

Introduction

Fructans are soluble fibers found in many plant-based foods; they are non-digestible oligosaccharides or polysaccharides. As oligosaccharides, they are part of the FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) and are similar to fructose and lactose.

They consist of heterogeneous fructose polymers (fructose units) and a glucose molecule and serve as storage carbohydrates in nearly 15% of flowering plants.

These compounds exhibit a range of health-promoting properties but cause gastrointestinal symptoms such as gas and diarrhea in intolerant individuals.

Table of contents

Fructan Types & Food Sources

Absorption & Metabolism

Fructan Intolerance

Fructan Intolerance & Fructose Intolerance

Fructan Intolerance or Other GI Disorders?

Health Benefits of Fructans

Prebiotic, Antioxidant & Immunomodulatory Effects

The Effects of Fructans on Health & Disease

Applications of Fructans

Summary

Sources

Fructan Types & Food Sources

Based on their structural bonds, fructans are classified into several groups (1, 2):

Inulin: Inulin-type fructans are the most studied type and are primarily found in chicory root, Jerusalem artichoke, dahlia, garlic, agave, and dandelion.
Levan: They are found in grasses such as ryegrass and bluegrass.
Graminan (mixed levan): They are commonly found in wheat, rye, barley, and oats.
Inulin neoseries: They are found in plants of the Liliaceae family.
Levan neoseries: They are considered rare and likely present only in oats.

Fructans are also classified into fructooligosaccharides (FOS) and oligofructans (OF) according to their degree of polymerization (2).

Fructans are mainly found in several plant families: the daisy family (e.g., daisy and chicory), the amaryllis family (e.g., amaryllis, garlic, onions, chives, and leeks), the asparagus family (e.g., asparagus and agave), grasses (e.g., corn, oats, wheat, spelt, barley, and rye), the lily family (e.g., aloe vera), and the Musaceae family (e.g., bananas) (3).

The table below shows the calculated values of fructans of various foods per 100g fresh weight (4).

Food	Fructan levels per 100g
Kidney beans, boiled	0.54g
Haricot beans, boiled	0.26g
Lima beans, boiled	0.29g
Lentils, boiled	0.14g
Split peas, boiled	0.73g
Textured soy protein (TSP)	1.1g
Soy yogurt, plain	0.14g
Wheat germ	2.5g
Jerusalem artichoke	16-20g
Garlic	9.8-16g
Onion	1.1-7.5g
Leek	0.5-7.1g
Asparagus	2-3g
Banana	0.7g
Rye bread (sourdough)	1.1g
Whole wheat bread	0.68g
Button mushrooms	0.27g
Kimchi	3.9-4.1g
Wakame flakes	0.04g

Another study calculated fructan values in foods per 100g fresh weight (5).

Vegetables	Fructans per 100g	Legumes	Fructans per 100g
Onion	1.97g	Canned peas	0.33g
Carrot	0.11g	Green beans	0.03g
Tomato	0.01g	Canned beans	0.24g
Lettuce	0.01g	Fruits	Fructans per 100g
Bell pepper	0.02g	Banana	0.11g
Cauliflower	0.09g	Apple	0.09g
Broccoli	0.02g	Orange	0.21g
Cabbage	0.03g	Grape	0.06g
Leek	0.24g	Pear	0.13g
Zucchini	0.01g	Tangerine	0.11g
Grain products	Fructans per 100g	Nuts	Fructans per 100g
White bread	0.14g	Almond	0.60g
Wheat flour	0.75g	Hazelnut	0.73g
Rolled oats	0.32g	Walnut	0.37g

Fructans are also present in burdock, raisin, Indian shot, palm, purple yam, potato, couscous, arrowroot, beet, Brussels sprouts, and aloe vera (6, 7).

Absorption & Metabolism

Human digestive enzymes cannot hydrolyze or break down fructans; instead, they are fermented by the colonic microbiota to produce short-chain fatty acids (SCFAs), lactic acid, and hydrogen (H2), lowering the pH of the colonic environment and making it more acidic.

SCFAs (acetate, propionate, and butyrate) are the primary metabolic by-products produced by bacterial fermentation of dietary fiber. They have anti-inflammatory and antioxidant effects, beneficially affect the immune system and metabolism, and regulate appetite and energy intake (1, 2, 8).

Additionally, it was found that fructans with a higher degree of polymerization (DP) are more likely to be fermented distally in the large intestine (1).

Fructan Intolerance

As mentioned above, fructans are fermented by the colonic microbiota and produce hydrogen and SCFAs. Additionally, they draw more water into the intestinal lumen. Only about 5-15% of fructans may be absorbed in the small intestine.

Individuals developing symptoms after fructan ingestion are considered fructan intolerant. The produced gas and bulking effects of fructans can result in bloating, abdominal distension, abdominal cramps/discomfort, flatulence (gas), and diarrhea in such individuals (11).

Fructan intolerance is more common in individuals with functional gastrointestinal (GI) disorders, such as irritable bowel syndrome (IBS); these individuals commonly benefit from low-FODMAP diets, including diets low in fructans. According to data, around 24% of IBS patients may develop GI symptoms after fructan intake. IBS patients with unexplained symptoms and negative for fructose and lactose intolerances and SIBO, a common finding during IBS, may test positive for fructan intolerance (11).

Fructan Intolerance & Fructose Intolerance

Fructan and fructose are both considered high FODMAP and lead to similar symptoms; however, they are different types of carbohydrates: fructose is a monosaccharide, whereas fructans are oligosaccharides.

High-fructose foods include the majority of fruits, especially fruit juices, canned and dried fruits (e.g., prunes, raisins, and dates), artichoke, asparagus, broccoli, chutney, leeks, mushrooms, okra, onions, peas, red pepper, shallots, most tomato products, wheat products, many marinated or processed meat products, and flavored milk and other yogurts (11).

Fructan Intolerance or Other GI Disorders?

Many gastrointestinal disorders, such as small intestinal bacterial overgrowth (SIBO), lactose intolerance, celiac disease, and non-celiac gluten sensitivity, may lead to similar symptoms.

Therefore, a healthcare professional is essential for a proper diagnosis and dietary restriction.

Health Benefits of Fructans

Prebiotic, Antioxidant & Immunomodulatory Effects

One of the main health benefits of fructans is linked to their prebiotic effects; fructans stimulate the growth of intestinal beneficial or probiotic bacteria, such as Lactobacillus and Bifidobacterium species, and decrease the number of pathogenic bacteria, such as Clostridium, thus improving the composition of the intestinal microbiota (1, 2, 7).

Moreover, fructans with higher DP values and in greater amounts are likely to have stronger probiotic effects (1).

Maintaining the normal composition of gut bacteria is essential for maintaining homeostasis in a healthy person. Gut bacteria provide the host with nutrients, metabolize indigestible compounds, help defend against harmful pathogens, help develop intestinal architecture, and stimulate the local immune system. The host controls gut microbiota composition by secreting antimicrobial peptides and immunoglobulins.

Prebiotic consumption is linked to modulated local and systemic immune parameters: got-associated lymphoid tissue or GALT, secondary lymphoid tissues, and peripheral circulation. GALT distinguishes between harmful and harmless agents, protects against infections, and avoids generating hypersensitivity reactions to gut bacteria and harmless antigens (2).

Another mechanism by which fructans promote the immune system is linked to the production of SCFAs. SCFAs reduce the growth of some pathogenic bacteria and increase mucin production. They also lead to the activation of G protein-coupled receptors (GPR), recruitment of white blood cells (WBC) to inflammatory sites, and suppression of the production of proinflammatory agents. Butyrate, a SCFA, decreases the requirement of glutamine for epithelial cells and beneficially alters gene expression (2).

Interestingly, recent animal studies proposed the role of fructans as ROS (reactive oxygen species) scavengers, suggesting that inulin may act as a barrier and protect the colonic mucosa against oxidative stress. Additionally, SCFAs have been reported to induce antioxidant enzyme levels and reduce NADPH oxidase in the colon (2, 7).

The Effects of Fructans on Health & Disease

Anti-diabetic effects.

Consumption of fructans may significantly reduce mean fasting blood glucose levels, improve insulin tolerance, and suppress insulin response to foods (2, 7, 9, 10).

Improved lipid metabolism and parameters

Fructan consumption may lead to decreased triglyceride and cholesterol levels and decreased liver, epididymal, inguinal, and subcutaneous fat tissue. It is also linked to decreased weight gain (2, 7, 10). Moreover, inulin and oligofructose may inhibit triglyceride synthesis, leading to decreased cholesterol levels (10).

Constipation relief

Fructans, such as inulin, are soluble dietary fibers that draw water into the intestines and act as a bulking agent, softening stool and relieving functional constipation symptoms in some individuals. The effective daily dose of inulin has been studied to be 15-20g (2, 7).

Improved mineral uptake

Fructooligosaccharides (FOS) are studied to stimulate fractional calcium and iron absorption (2, 9).

Regulated gut peptides and satiation

Fructans may increase glucagon-like peptide-1 and glucagon-like peptide-2 concentrations, reduce ghrelin levels, and induce satiety (2, 7, 9).

Body weight and energy intake reduction by the induction of satiety (2).
Decreased risk of tumors and cancers

Fructans are linked to a decreased risk of cancers, predominantly gastrointestinal, due to prebiotic effects, SCFAs, and enhanced responses for IFN-γ on CD8+T cells. Additionally, inulin may enhance the anti-tumor efficacy of immunotherapy with PD-1 inhibitors (7, 9, 10).

Decreased risk of bad breath

According to a study, inulin decreases the tongue pH and stimulates oral acidic microbiota, thus reducing the chances of halitosis or bad breath (7).

Applications of Fructans

Fructans, mostly inulin and inulin-type, are widely used in several industries. They are used as fat and sugar substitutes and in tequila production.

Fructans and galactooligosaccharides are major components in forming prebiotic foods on the industrial scale.

Inulin enhances the sensory formulation of foods by increasing their size and texture. It also protects foods from browning during heating, prevents food drying, and lowers the freezing temperature of foods.

Fructans can be used to produce high fructose syrup instead of starch or sucrose (sugar). DFAs, which are synthesized from inulin, may be used as a low-calorie sugar alternative.

Interestingly, inulin-containing plant waste may be used in biofuel and co-product production (7).

Summary

Fructans are soluble fibers found in many plants. The primary sources of fructans are chicory, Jerusalem artichoke, garlic, dahlia, agave, dandelion, wheat, rye, barley, oats, ryegrass, and bluegrass.

Human digestive enzymes cannot break down fructans; instead, they are fermented by the colonic microbiota to produce SCFAs, lactic acid, and hydrogen (H2). Fructans stimulate the growth of probiotic bacteria and decrease the number of pathogenic bacteria, thus improving the normal composition of the intestinal microbiota and showing immunomodulatory effects.

Fructans exhibit a range of health-promoting properties, including prebiotic, antioxidant, immunomodulatory, anti-inflammatory, anticancer, and antidiabetic properties; they also improve constipation symptoms and lipid metabolism, regulate gut peptide levels, and aid in weight loss.

Individuals developing symptoms after fructan ingestion are considered fructan intolerant. The produced gas and bulking effects of fructans can result in bloating, flatulence (gas), abdominal cramps or discomfort, and diarrhea in such individuals.

Sources

Author name: Arpi Gasparyan

Education: General Medicine at YSMU

Last updated: August 09, 2024

Medically reviewed by Elen Khachatrian