Some people with irritable bowel syndrome (IBS) are sensitive to fermentable carbohydrates called FODMAPs. Fructans are a type of FODMAP commonly found in foods like wheat, onions, and garlic, and are among the most common FODMAP triggers (along with galacto-oligosaccharides, or GOS) for people with IBS.
Some individuals with fructan intolerance may experience digestive symptoms after eating foods containing fructans. Abdominal bloating and pain are two of the most common and distressing symptoms associated with fructan intolerance.
This article will cover what fructans are, which foods contain them, how fructans fit into a low FODMAP diet, and tips for identifying and managing fructan intolerance.
Introduction to Fructans
Fructans are a type of carbohydrate found in many foods that we eat every day, including wheat, onions, garlic, and a variety of fruits and vegetables. Classified as fermentable oligosaccharides, fructans are made up of chains of fructose molecules. The human body has a limited ability to break these carbohydrates down in the small intestine. As a result, fructans pass through the digestive tract undigested until they reach the colon, where they are fermented by gut bacteria.
For most people, this process is harmless. However, for individuals with IBS or other functional gastrointestinal disorders, the fermentation of fructans can lead to uncomfortable gastrointestinal symptoms such as bloating, gas, and abdominal pain. Because fructans are just one group within the broader category of fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs), they are a key focus of the low FODMAP diet.
This specialized diet restricts certain fermentable carbohydrates to help manage symptoms and determine your individual food triggers and tolerated portion sizes. Understanding where fructans are found and how they affect the body is an important first step in managing symptoms and making informed dietary choices.
What Are Fructans?
As mentioned, fructans are a type of FODMAP. Advances in food chemistry have led to the development of digestive enzymes that can help break down certain FODMAPs (including fructans) for individuals with sensitivities (we'll dive into this later in this article).
There are five FODMAP categories, including:
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Excess fructose: A simple sugar (monosaccharide) found in foods like apples, apricots, and pears.
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Fructans: An oligosaccharide made of long chains of fructose, often with a sucrose (fructose + glucose) molecule at one end. Inulin-type fructans are a specific subclass characterized by longer fructose chains and are often used as dietary fiber or sugar replacements in food formulations due to their functional properties. Beyond inulin, other types of fructans include graminan, levan and agavin.
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Galacto-oligosaccharides (GOS): An oligosaccharide made of 2 to 8 galactose sugars joined together with a glucose molecule at the end.
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Lactose: A disaccharide made of glucose and galactose joined together.
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Polyols (mannitol and sorbitol): Also called sugar alcohols, polyols are molecules with two or more hydroxyl groups (an oxygen and hydrogen atom bonded to a carbon atom) attached to a carbon backbone.
Fructans and other FODMAPs help certain foods, such as vegetables, fruits, and cereals, store carbohydrates. While most people with IBS are sensitive to several FODMAP groups, it’s rare for a person to be sensitive to all five FODMAP categories.
Why Fructans Cause Digestive Symptoms
The reason fructans sometimes cause digestive symptoms is related to how they’re digested. Fructans do not fully break down in the digestive tract (in fact, only about 5% to 15% of fructans are absorbed; most end up feeding gut bacteria or are excreted). This is because humans lack the enzymes (fructan hydrolases) to break down fructans before they reach the colon. Instead, undigested fructans reach the colon intact, similar to how undigested lactose does in people with lactose intolerance. Both conditions involve undigested carbohydrates that lead to uncomfortable digestive symptoms, but in the case of fructan intolerance the body does not make an enzyme to break down fructans
FODMAPs, like fructans and GOS, are important “food” for gut bacteria. These bacteria feed on FODMAPs by fermenting them, which produces gas. While the pressure of the gas on your intestinal walls typically doesn’t cause symptoms, it can be perceived as painful by people with visceral hypersensitivity. Visceral hypersensitivity is common in people with IBS, and, in simple terms, describes a condition where your organs—especially those in your gut—are extra sensitive to normal sensations. This means that the gas that is produced by your gut bacteria as a normal part of fructan digestion may be extremely painful for people with visceral hypersensitivity.
Fructan intolerance is common in people with IBS, with some studies estimating that over half of people with IBS are sensitive to fructans. Even small portions of high-fructan foods (like onions and garlic) can trigger symptoms, making managing fructan intolerance tricky. Fructose (another FODMAP) malabsorption can also contribute to symptoms, and breath testing is sometimes used to distinguish between fructan and fructose intolerance.
Symptoms of Fructan Intolerance
There are many possible symptoms of fructan intolerance, but some of the most common include:
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Gas
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Bloating
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Distention
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Cramping
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Abdominal pain
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Intestinal noises
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Altered bowel movements
Some individuals may experience symptoms such as abdominal bloating and altered bowel movements, and severe symptoms can occur even with small amounts of fructans. People with fructan intolerance may experience symptoms that significantly impact their daily life.
It’s important to note that not all people with IBS have fructan intolerance, and not all people with fructan intolerance have IBS. Additionally, some people who think they’re gluten-intolerant may actually be intolerant to fructans.
What’s the difference between gluten and fructans? Most basically, gluten is a type of protein, while fructans are a type of carbohydrate. Gluten can cause digestive problems and must be strictly avoided by those with celiac disease, whose bodies mount an autoimmune reaction to gluten that damages their small intestinal wall.
But what about non-celiac gluten sensitivity? While it’s true that some people without celiac disease do have reactions to gluten, most people are actually reacting to the fructans found in gluten-containing foods. That’s why some people with IBS feel better when they cut out foods with gluten, like wheat bread and pasta. Since many gluten-containing foods also contain fructans, removing those fermentable fructans from the diet may, in fact, be what’s providing relief.
This highlights the importance of working with a registered dietitian who can help you understand your individual food triggers and develop a plan for managing fructan intolerance that doesn’t involve over-restricting your diet.
Foods High in Fructans
There are many foods high in fructans, including grains such as wheat, barley, and rye; vegetables such as onions, garlic, and leeks; some fruits such as cranberries, dried figs, and ripe bananas; legumes such as kidney beans; nuts like cashews and pistachios; and food additives like inulin, fructo-oligosaccharides (FOS) and chicory root.
High-fructan foods that contain gluten include wheat, spelt, rye, and barley, while high-fructan foods that do not contain gluten include garlic, onions, artichokes, and certain fruits. Inulin and chicory root are often added to 'fiber-enriched' or 'low-calorie' processed foods. Processed foods and processed grains can also be significant sources of fructans, so it's important to check ingredient labels, especially if you are sensitive to fructans.
Different foods contain different amounts of fructans. That means that different portion sizes of different high-fructan foods, as well as how many moderate-to-high fructan foods you’ve eaten throughout the day (known as cumulative FODMAP load), can have different effects on different people.
If you’re unsure which FODMAPs you may be sensitive to, it can be beneficial to do a short-term FODMAP elimination for 2 to 6 weeks, followed by structured reintroduction. You can also try a fructan-targeting enzyme with meals for several days to see if your symptoms improve.
If eliminating FODMAPs, reintroducing them is critical for identifying your personal FODMAP triggers and the portion sizes you can tolerate so that you don’t have to restrict your intake forever. It’s important not to skip this step.
There are a few situations where limiting fructans temporarily may be helpful, including:
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If you’re in an active IBS flare, reducing your FODMAP intake (including fructans) for a few days to let your digestive system settle can be helpful.
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If you’re undertaking the low FODMAP diet to identify your food triggers, you will need to limit your intake of all FODMAPs (including fructans) for 2 to 6 weeks.
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If you consistently notice that you get symptoms when you eat high-fructan foods, you may need to take digestive enzymes containing fructan hydrolase so you can eat these foods with fewer symptoms.
However, fructans are prebiotics (food for your gut microbiome), so avoiding them long term could reduce your gut microbiome diversity because you’re restricting one of your bacteria’s main food sources.
And the nutritional and social downsides shouldn’t be ignored either. Eating out at restaurants or events like weddings can be difficult when you’re avoiding a long list of foods. This highlights the importance of working with a dietitian who can guide you through the low FODMAP diet and help you determine which FODMAPs you’re sensitive to. It’s rare for someone to be sensitive to all FODMAPs at all portion sizes, so learning which ones you can tolerate is key to expanding your dietary variety.
Grains and Grain-Based Foods
Grain and grain-based foods are some of the most common fructan-containing foods, and include the following foods:
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Wheat (bread, pasta, cereals, farro, bulgur, cous cous, bran)
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Barley
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Rye
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Baked goods made with wheat flour
Both fructose and fructans can be present in these foods, so determining which one you're sensitive to is important for individuals with sensitivities.
Because these foods contain both gluten and fructans, fructan intolerance is often confused with gluten sensitivity. However, some gluten-free foods are not suitable for people with fructan intolerance because they contain high levels of fructans, such as inulin (often added as a fiber booster or sweetener).
Vegetables
Several aromatic and cruciferous vegetables are high in fructans, including:
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Garlic
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Onions
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Leeks (white part)
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Shallots
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Broccoli
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Cabbage
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Brussels sprouts
Garlic and onion are common triggers because even small amounts can cause symptoms. They're also used as seasonings in a wide variety of foods, so it's easy to accidentally eat onion or garlic, which can lead to gut symptoms.
Fruits
Not many fruits contain fructans, but dried fruit often does. Here are some of the fruits that contain fructans:
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Cranberry
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Dried fruit
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Ripe banana
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Dates
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Certain melons in large portions
Remember, fructans differ from excess fructose. Fructose is a monosaccharide (single sugar), while fructans are long chains of fructose, usually with a sucrose molecule on one end.
Legumes, Nuts, and Other Sources
Legumes and nuts are both high in fructans, and some varieties also contain another oligosaccharide called GOS. Here are some other sources of fructans:
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Chickpeas (some people can tolerate canned, drained chickpeas in portion sizes up to ¼ cup)
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Lentils (some people can tolerate canned, drained lentils in portion sizes up to ¼ cup)
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Kidney beans
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Black beans
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Cashews
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Pistachios
When you're sensitive to fructans, it's important to be mindful of fructan stacking. This is where you eat several foods that may contain only moderate amounts of fructans, but the total amounts add up enough to trigger symptoms.
Think of fructan stacking as filling a bucket. When you combine multiple fructan-containing foods in one meal, the bucket may overflow past your personal tolerance. This doesn't mean you need to avoid all fructans, but you may need to be mindful of portion sizes and timing.
How to Identify Fructan Sensitivity
While it’s best to work with a professional who can help you identify food intolerances, here are some simple steps you can take yourself to determine whether you might have a fructan sensitivity:
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Look for patterns: Notice whether symptoms such as bloating, gas, or abdominal discomfort occur after eating foods containing wheat, onion, or garlic.
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Keep a simple food and symptom journal: Track what you eat, when symptoms start, and how intense they feel for one or two weeks. It’s also important to track other variables like stress levels, sleep patterns, and exercise, as these can also trigger IBS symptoms.
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Avoid self-diagnosing after one bad meal: Stress, large portions, or fatty foods can mimic fructan sensitivity.
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Try a structured approach: A low FODMAP diet elimination followed by structured reintroduction is one of the most reliable ways to test fructan intolerance.
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Work with a professional when possible: A GI dietitian can help rule out other conditions and prevent unnecessary restriction.
Using a Low FODMAP Diet
The low FODMAP diet is a short-term dietary approach to help you determine your individual food triggers and tolerated portions. It starts with a short elimination phase lasting 2 to 6 weeks, during which high FODMAP foods are replaced with lower FODMAP alternatives. A low fructan diet is often used as a management strategy for those with fructan sensitivity or intolerance.
After the initial elimination, foods are systematically reintroduced to test tolerance. Testing for fructan tolerance typically involves reintroducing several fructan-containing foods one at a time, since fructans from wheat, onion, garlic, fruits, and vegetables can affect people differently. Testing foods one at a time in set portions helps you understand your personal triggers and tolerance levels.
To achieve clear results, it’s important to minimize confounding variables during the reintroduction phase by keeping stress levels low, prioritizing sleep, maintaining a consistent fiber intake, and avoiding introducing multiple new foods at once. This helps you link symptoms to the single food being tested.
Food Journaling and Symptom Tracking
Keeping a detailed food and symptom journal can help you draw connections that may not be obvious day to day. Here are some things to consider tracking:
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Food eaten, including portion size and timing
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Digestive symptoms and when they occur (including bloating, gas, pain, bowel changes)
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Stress levels
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Menstrual cycle
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Supplements and medications
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Exercise
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Changes to your normal routine, such as travel
These factors can all influence gut symptoms and can help explain why the same food may only trigger symptoms on certain days. Patterns that suggest fructan intolerance include symptoms that occur a few hours after eating food like garlic, onions, and wheat. Repeated bloating or discomfort after higher-fructan days, but not on lower-fructan days, can be a useful clue that you may be fructan intolerant.
Managing High Fructan Foods Without Full Elimination
Ideally, you’ll move past the strict restriction of high FODMAP foods and shift to improving tolerance and building flexibility in your diet. Fructans are an important source of prebiotics that can support a healthy gut microbiome, so including them in amounts you can tolerate is important for promoting overall gut health. Fructans also support immune function by nourishing beneficial gut bacteria, which can help bolster your immune system.
Dietary and Lifestyle Strategies
There are several dietary and lifestyle strategies that can help improve fructan tolerance:
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Pair fructan-containing foods with protein and fat: While adding protein or fat doesn't "cancel out" fructans, mixed meals can slow digestion, which may help reduce rapid fructan fermentation in the gut for some people.
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Eat slowly and chew your food well: Thorough chewing starts mechanical digestion and may reduce swallowed air, which can lessen gas and bloating with high-fructan meals.
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Be mindful of garlic and onion portions: Both are very high in fructans, so if you have fructan intolerance, try limiting your intake or use a digestive enzyme supplement containing fructan hydrolase.
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Gentle movement after meals: A short walk can stimulate gut motility and help clear gas.
Smart Substitutions and Preparation Methods
A few smart swaps or different preparation methods can go a long way in reducing your fructan intake:
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Use garlic- or onion-infused oils: Fructans are water-soluble, not fat-soluble, so infused oils provide flavor without the fermentable carbohydrates.
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Choose low FODMAP seasoning blends: Check the label for onion and garlic powder.
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Choose low-fructan grains: Swapping wheat-based grains for options like rice, quinoa, or traditionally fermented sourdough can help reduce fructan-related symptoms.
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Soak or use canned legumes: Soaking legumes and discarding the soaking water, or using canned, rinsed legumes, reduces the amount of fermentable carbohydrates.
Digestive Enzymes for Fructan Breakdown
Digestive enzyme supplements can help you expand your diet to include more high-fructan foods. Fructan hydrolase breaks down a wide range of fructans (including inulin, levan, graminan, agavin, and FOS), while inulinase targets inulin specifically. Alpha-galactosidase breaks down GOS but not fructans.
Enzymes can reduce symptoms by breaking fructans into smaller sugars before they reach the colon, thereby reducing bacterial fermentation. However, they don’t “cure” IBS, and extremely large FODMAP portions may still cause symptoms if you don’t use enough digestive enzymes. Enzymes can be particularly useful when you don’t have control over your food, such as when eating out or traveling.
Using FODZYME With High Fructan Foods
If you want to expand your dietary variety and reduce anxiety around high FODMAP foods while minimizing digestive symptoms, a targeted enzyme supplement like FODZYME can help.
FODZYME contains digestive enzymes to break down fructans, GOS, and lactose. Sprinkling it on your meal helps break down fructans before they reach your large intestine, reducing bacterial fermentation and potentially easing symptoms like gas, bloating, and abdominal discomfort.
Try FODZYME today and enjoy more freedom to enjoy the foods you love with less discomfort.
High Fructan Foods FAQ
What's the Difference Between Fructans vs. Gluten Intolerance?
If you've ever tried going gluten-free to solve your digestive problems without it making a difference, it may not be gluten intolerance. Since products like wheat and barley contain both gluten (a protein) and fructans (a fermentable carbohydrate), fructan intolerance is often misattributed to gluten. However, many foods that contain fructans don't contain gluten, so it's important to work with a healthcare professional to determine the true cause of your symptoms. While celiac disease (an autoimmune reaction to gluten) may cause some of the same symptoms of fructan intolerance, it can also cause symptoms like unintentional weight loss, iron-deficiency anemia, joint pain, and skin rashes. It's important to determine whether you're dealing with celiac disease or fructan intolerance, as the treatments are very different.
Are All Fructans Bad?
Fructans are not "bad," although because they're rapidly fermented in the colon, they may cause uncomfortable digestive symptoms in some people. However, small amounts may be tolerated, especially when paired with a digestive enzyme supplement containing fructan hydrolase. Ideally, you should not over-restrict fructans, as they can support a healthy gut environment by acting as food for your gut microbiome.
What Vegetable Is Highest in Fructans?
Garlic is the highest-fructan vegetable, followed closely by Jerusalem artichoke.
Is Oatmeal a Fructan?
While rolled oats do contain fructans, they are considered to be low FODMAP at serving sizes of half a cup. Larger portions contain more fructans and may trigger symptoms for people with fructan intolerance.
Why Am I Suddenly Sensitive to Fructans?
While the exact cause of fructan intolerance is not well understood, some people appear to have less capacity to digest fructans than others. Combined with visceral hypersensitivity, this can lead to uncomfortable digestive symptoms. Other factors, like stress and poor sleep, can also reduce your tolerance to high FODMAP foods by lowering your pain threshold, so if you're currently experiencing significant stress or poor sleep, this could explain why you're suddenly sensitive to fructans. Additionally, some small studies suggest that gastroenteritis or food poisoning can trigger sensitivity to FODMAPs, including fructans. This is known as post-infectious IBS.