What Category is a Fructan in? Understanding the Carb Connection

January 5, 2026 •

4 min read

According to researchers, fructans are the most common FODMAP to trigger gastrointestinal symptoms for individuals with Irritable Bowel Syndrome (IBS). This makes understanding the carbohydrate category that a fructan falls into crucial for many who seek digestive relief. Fructans are not a single molecule but a complex family of sugars that are often misunderstood.

Quick Summary

Fructans are complex carbohydrates classified as oligosaccharides and are part of the broader group known as FODMAPs. They are composed of fructose chains that are poorly digested in the small intestine, leading to fermentation by gut bacteria in the colon, which can trigger symptoms for sensitive individuals.

Key Points

Fructans are Oligosaccharides: They are a category of complex carbohydrates made of chains of fructose molecules.
Fructans are Part of FODMAPs: In the FODMAP acronym, fructans belong to the 'O' category, which stands for oligosaccharides.
Not Easily Digested by Humans: The human digestive system lacks the enzymes required to break down fructans in the small intestine.
Fermented in the Colon: Undigested fructans pass into the large intestine, where they are fermented by gut bacteria, producing gas.
Cause Digestive Issues in Some: For individuals with IBS or other functional gut disorders, this fermentation process can cause symptoms like bloating, gas, and pain.
Found in Diverse Foods: Fructans are present in various foods, including wheat, onions, garlic, and asparagus.
Mistaken for Gluten Sensitivity: Some individuals who experience digestive issues after eating wheat may actually be reacting to fructans, not the gluten.

Fructans: A Complex Carbohydrate Explained

Fructans are a type of carbohydrate, but to fully understand their impact, one must look beyond this basic classification. Specifically, fructans belong to the oligosaccharide family, which is a key component of FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols). FODMAPs are short-chain carbohydrates that the small intestine poorly absorbs. This malabsorption is the primary reason why fructans can cause digestive issues like bloating, gas, and abdominal pain in some people, particularly those with conditions such as Irritable Bowel Syndrome (IBS).

The Role of Fructans in the Plant Kingdom and Diet

Plants use fructans as a storage carbohydrate, similar to how they use starch. They are found in a wide variety of plant-based foods, and their presence is not always obvious. For example, fructans are major components in wheat, barley, onions, and garlic, making them a significant part of many people's diets. For most people, these carbohydrates are beneficial, acting as a prebiotic that feeds healthy gut bacteria. However, the same fermentation process that benefits the gut microbiome can cause discomfort for sensitive individuals.

The Different Types of Fructans

Fructans are not a single compound but a family of polymers made of fructose molecules. These can vary in their chain length and chemical structure, which influences how they are fermented in the gut.

Fructo-oligosaccharides (FOS): These are shorter-chain fructans, typically made of 2 to 9 fructose units. They are rapidly fermented in the colon, which can quickly produce gas and symptoms in sensitive individuals. FOS is found naturally in many foods and is often added to processed foods as a prebiotic fiber.
Inulin: This type of fructan has a longer chain length, with 10 or more fructose molecules. Inulin is commonly found in foods like chicory root and asparagus. Its longer chain structure means it ferments more slowly, but it can still trigger symptoms in those with fructan sensitivity.
Levan and Graminan: These are other classifications of fructans based on their glycosidic linkages. Levans have different bonds than inulins and are common in grasses, while graminans are branched fructans found in cereals like wheat and barley.

Fructan Intolerance vs. Gluten Intolerance

There is a significant misconception that sensitivity to wheat products is always due to gluten, a protein. However, the symptoms people experience after consuming wheat, such as bloating and abdominal pain, are often caused by the fructans present in the grain, not the gluten. Fructans are carbohydrates, while gluten is a protein, and the body digests and processes them differently. This is a crucial distinction for many people with digestive issues. Someone may incorrectly assume they have gluten sensitivity when they are actually reacting to fructans, making it necessary to explore options like the low-FODMAP diet to identify the true trigger.

The Low-FODMAP Diet and Fructans

The low-FODMAP diet is a therapeutic elimination diet often used to manage symptoms of IBS and other functional gut disorders. It involves a temporary removal of high-FODMAP foods, including those rich in fructans, followed by a systematic reintroduction to determine individual tolerance levels. Given that fructans are a common trigger, identifying and understanding one's sensitivity to them is a key step in this process. A registered dietitian can guide this process to ensure nutritional needs are met while isolating problematic food components.

Fructan Digestion vs. Fructose Digestion


Aspect	Fructan Digestion	Fructose Digestion
Carbohydrate Type	Oligosaccharide (chain of fructose molecules)	Monosaccharide (single fructose molecule)
Enzymatic Digestion	Human body lacks enzymes to break down fructan chains in the small intestine.	Absorbed directly through the small intestine, though some individuals may have malabsorption.
Absorption	Poorly absorbed, with most passing into the large intestine.	Efficiently absorbed, though large quantities can overwhelm absorption capacity in some people.
Colon Interaction	Fermented by gut bacteria, producing gas, which leads to bloating and pain.	Excess amounts reach the large intestine and are fermented, causing similar but distinct symptoms from fructans.
Dietary Sources	Wheat, onions, garlic, and chicory root.	High-fructose corn syrup, honey, and various fruits.

Conclusion

In summary, a fructan is a complex carbohydrate that falls into the oligosaccharide category and is a major subgroup of FODMAPs. It is not a single entity but a diverse family of fructose polymers, such as inulin and FOS, that are widely present in plant-based foods. The inability of the human small intestine to break down these molecules leads to their fermentation in the colon, which can cause significant gastrointestinal distress for sensitive individuals. By distinguishing fructans from other dietary components like gluten and understanding their place within the broader FODMAP framework, those with digestive sensitivities can make more informed dietary choices to manage their symptoms effectively. Consulting with a healthcare professional or dietitian is the best approach for anyone considering changes to their diet based on fructan content.

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

Frequently Asked Questions

Yes, fructans are a type of carbohydrate, which is a sugar. Specifically, they are complex sugar chains made of fructose molecules. They are not to be confused with fructose, the simple sugar, though they are related chemically.

Fructose is a single sugar molecule (a monosaccharide), whereas fructans are chains of fructose molecules (oligosaccharides). The human body can absorb fructose, but it lacks the enzymes to break down and absorb fructans, which is why fructans can cause digestive issues.

FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols. Fructans are the 'O' in this acronym, representing oligosaccharides.

Fructans are hard to digest because the human body does not produce the specific enzymes, like fructan hydrolase, needed to break the bonds linking the fructose units. This causes them to pass largely intact into the large intestine.

Common foods high in fructans include wheat, onions, garlic, barley, rye, and asparagus. Inulin, a long-chain fructan, is also added to many processed foods to increase their fiber content.

Yes, fructan intolerance is often mistaken for gluten intolerance. Many high-fructan foods, like wheat, also contain gluten. The digestive symptoms experienced may actually be a reaction to the fructans, not the gluten protein.

Identifying a fructan sensitivity is typically done through an elimination diet, such as the low-FODMAP diet. Under the guidance of a dietitian, high-fructan foods are removed and then systematically reintroduced to observe any symptoms.