Fructans: Foods, Sensitivity, and Digestive Health

Fructans are a type of carbohydrate found in many commonly eaten foods, but for some people, such as those with functional gut disorders like irritable bowel syndrome (IBS), they can cause uncomfortable digestive issues. 

If you've ever noticed that certain foods, like garlic, onions, or wheat, cause you to become bloated, gassy, or generally uncomfortable, fructans may be to blame. These small carbohydrates are difficult to digest because the human body lacks the enzymes needed to break them down.

Managing fructan sensitivity often involves identifying and avoiding foods high in fructans, and for many, the low-FODMAP diet is a helpful tool. However, this diet is very restrictive, and following it long-term isn't recommended. Luckily, digestive enzyme supplements like FODZYME can offer relief to people with fructan sensitivities, making it easier to enjoy a wide variety of foods without gut symptoms.

In this article, we'll cover everything you need to know about fructans, from how they cause issues in the gastrointestinal tract to which foods are highest in fructans. Plus, we'll review how digestive enzymes can help with the long-term management of a fructan intolerance.

What Are Fructans?

Fructans are a type of FODMAP. FODMAPs stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols. Fructans are a type of oligosaccharide – the "O" in FODMAP. While they sound similar, they differ from fructose molecules, a monosaccharide (the "M" in FODMAP) or simple sugar. Fructose malabsorption only occurs when there are more fructose molecules than glucose molecules, whereas fructans are not absorbed in any amount.

Fructans are carbohydrates made of chains of fructose, often with a glucose molecule at one end. Fructans with 2–9 fructose molecules are called "oligofructose" or "fructo-oligosaccharides" (FOS), while those with more than 10 fructose molecules are called "inulins." These inulin-type fructans are often added to foods as a sugar replacement or a fiber booster.

The role of fructans in the diet

Fructans are a type of prebiotic fiber. Prebiotic fibers feed the good bacteria in your gut. You can think of prebiotic fibers (such as fructans) as a food source specifically for these good gut microbes.

Unlike other nutrients that get digested and absorbed before they reach the large intestine, prebiotic fibers pass through to the large intestine intact. Here, these fermentable carbohydrates act as fuel for the good gut bacteria. By feeding these bacteria, prebiotic fibers can help support digestion, immune function, and overall gut health.

How the body processes fructans

The human digestive system struggles to digest fructans in the small intestine, and only about 5% – 15% of fructans are absorbed. This is because the human body lacks the enzymes needed to break apart the glycosidic linkages (bonds) connecting the simple sugars that make up a fructan molecule. 

When fructan-containing foods reach the large intestine undigested, they get fermented by the gut bacteria, which can cause gas. Plus, since fructans are a small molecule, they pull water into the large intestine, which can cause bloating, diarrhea and additional gas. This is similar to what happens when people with lactose intolerance eat foods containing lactose.

It's important to note that fructans do not cause digestive issues for everyone. However, for those with a FODMAP intolerance (such as people with irritable bowel syndrome, or IBS), the non-digestible fructans can cause some seriously frustrating gut symptoms. In fact, some studies show that fructans are the most common FODMAP to trigger symptoms. A 2021 study found that fructans and galacto-oligosaccharides (GOS) were the most common FODMAPs associated with worsening abdominal pain. Another 2024 study found that fructans were the most common FODMAP trigger, causing symptoms in 56% of study participants.

Foods High in Fructans

Many foods are high in fructans, from whole and processed grains to certain fruits and vegetables. Here are some of the most common foods high in fructans:

  • Wheat (bread, pasta, etc.)
  • Barley
  • Spelt
  • Rye
  • Onions
  • Garlic
  • Shallots
  • Scallions (the white part)
  • Leeks (the white part)
  • Asparagus
  • Brussels sprouts
  • Cabbage (such as Savoy cabbage)
  • Artichoke
  • Watermelon
  • Persimmon
  • Ripe banana
  • Red kidney beans
  • Navy beans
  • Black beans
  • Lima beans
  • Pistachio
  • Cashews
  • Inulin
  • Chicory root

Consider using the Monash or FODMAP Friendly apps for the most up-to-date information about which foods are high in fructans.

Fructan Sensitivity and Intolerance

Fructan sensitivity and fructan intolerance can be used interchangeably, and the symptoms are similar to what many people with IBS experience when they eat FODMAPs.

Common symptoms of fructan sensitivity

Common symptoms of fructan intolerance are typically digestive symptoms such as:

  • Gas
  • Abdominal bloating
  • Abdominal pain
  • Constipation
  • Diarrhea

These common IBS symptoms can range from mild to severe. Often, gastrointestinal symptoms will be worse the more fructans someone with a fructan intolerance eats. However, some people are very sensitive to fructans and may experience severe symptoms even after eating a small amount of fructans.

How fructans trigger digestive discomfort

Remember, fructans aren't digested but instead enter the large intestine intact. Once they reach the large intestine, they act as food for the good gut bacteria. After being fermented by the gut bacteria, they produce gas. Since they're small molecules, fructans also pull water into the large intestine.

The production of gas and the pulling of water into the large intestine stretches the colon. For most people, this doesn't cause too many issues beyond some mild gas and bloating. However, for people with a fructan intolerance, such as those with IBS, it can cause troublesome digestive symptoms.

This is thought to occur because people with IBS experience visceral hypersensitivity. This means that the nerves in the digestive system are extra sensitive. When the large intestine stretches in response to gas production and water introduction into the large intestine, it's perceived as painful due to this heightened sensitivity. However, other factors like gut dysbiosis (an imbalance of beneficial and harmful bacteria) and inflammation may also be at play. Research into the exact causes of IBS remains ongoing.

Managing Fructan Sensitivity

People with fructan sensitivity may benefit from identifying and avoiding high-fructan foods. The low-FODMAP diet is a common approach to managing fructan intolerance. This diet involves temporarily removing all high-FODMAP foods for a while (typically 2–6 weeks) to get symptoms under control and determine whether FODMAPs cause their symptoms. 

However, the low-FODMAP diet isn't right for everyone, and people with or at risk of disordered eating, children, the elderly, and those at risk for malnutrition should avoid it and use other management strategies, such as digestive enzymes.

Once you've completed the elimination phase of the low-FODMAP diet, you'll move on to the reintroduction phase. This is where you'll find out whether you're sensitive to fructans. During the reintroduction phase, you reintroduce FODMAPs one group at a time. If you develop symptoms when you reintroduce high-fructan foods (like onion, garlic, and wheat), you likely have a fructan intolerance.

Identifying and avoiding high-fructan foods

The best way to identify high-fructans foods is to use the Monash or FODMAP Friendly apps. These apps allow you to search a wide variety of different foods. When you select a food, the app will tell you which kind of FODMAPs the food contains. For example, when you search "garlic," the apps will tell you that garlic is high in fructans.

Another feature of the Monash app is the filtering system. This feature allows you to filter foods by type of FODMAP. If you're intolerant to fructans, you can select fructans, and the food lists will have a red traffic light next to them if they contain any amount of fructans. This makes it easy to identify high-FODMAP foods at a glance. If a food doesn't have a red traffic light symbol next to it, it's low in fructans and shouldn't cause symptoms for people with a fructan intolerance.

You may also find it helpful to shop for low-FODMAP foods on an online store  specializing in low-FODMAP food products.

Low-fructan food alternatives

If you need to reduce fructans in your diet, there are plenty of low-fructan options available. Here are a few substitutions for common high-fructan foods

  • Instead of onions, try using the green parts of green onions or chives for added flavor.
  • Instead of garlic, try garlic-infused oil, which doesn't contain the fructans contained in garlic cloves.
  • Substitute wheat products for gluten-free grains like rice or oats, which are generally low in fructans (keep in mind, it's not actually the gluten you need to avoid. Gluten is a protein, while fructans are a carbohydrate, and gluten intolerance is different from fructan intolerance. However, gluten-free products are generally wheat-free, making them low in fructans).

For a more comprehensive list of low-FODMAP foods, check out our article about FODMAP intolerance and the low-FODMAP diet.

The Low-FODMAP Diet and Fructans

Fructans are one of the primary FODMAP groups, so they're avoided during the elimination phase of the low-FODMAP diet. 

Where fructans fit into a low-FODMAP diet

Fructans are the "O" in FODMAP – oligosaccharides. Galacto-oligosaccharides (GOS) are also part of the oligosaccharides group.

The other FODMAP groups include disaccharides (lactose), monosaccharides (excess fructose), and polyols (sugar alcohols like sorbitol and mannitol). These short-chain carbohydrates can all cause symptoms because the intestinal bacteria feed on them. Plus, they pull water into the large intestine, which can stretch the walls of the bowel, causing pain in people with functional gastrointestinal disorders like IBS.

Balancing fructans with other FODMAPs

Balancing fructan-containing foods with other FODMAPs is important, as eating many low- or medium-FODMAP foods at once can lead to FODMAP "stacking." This happens when several FODMAPs are consumed at once, which can amplify symptoms. 

This is where using an app can come in handy. In addition to telling you which foods are high in fructans (or other FODMAPs), the Monash and FODMAP Friendly apps can tell you which foods have a moderate amount of FODMAPs. While eating one of these foods might not trigger symptoms, eating several moderate FODMAP foods throughout the day can add up and may lead to symptoms.

Digestive Support for Fructan Sensitivity

Fortunately, advances in food chemistry and technology have led to the development of enzymes that can help digest fructans. Since the human body lacks the enzymes needed to properly break down fructans, leading to high-fructan foods being poorly absorbed, digestive enzyme supplements containing fructan hydrolase (the enzyme that breaks down fructans) may be helpful for people with fructan sensitivity. 

The role of enzymes in digesting fructans

Using a digestive enzyme supplement like FODZYME may be beneficial when following a low fructans diet isn't practical or when trying to reintroduce small amounts of fructans to gauge your tolerance. They can also help you avoid making unnecessary dietary restrictions.

FODZYME is a digestive enzyme supplement specifically designed to help break down fructan-containing foods and other problematic FODMAPs, all while avoiding gut symptoms. It contains three enzymes – fructan hydrolase (to break down fructans), alpha-galactosidase (to break down GOS), and lactase (to break down lactose).

By providing the enzymes the body lacks to digest fructans and other FODMAPs, FODZYME helps reduce the fermentation process in the gut that leads to gas, bloating, and digestive discomfort. This is because the enzymes in FODZYME digest the FODMAPs before your gut bacteria can feed on them. This may make you less likely to experience symptoms when you eat high-fructan food.

For people with fructan sensitivity, FODZYME can make it easier to enjoy high-fructan food without triggering symptoms. If you struggle with fructan-rich foods like garlic, onions, or wheat, FODZYME could be a practical solution to support your digestion.

Click here to support your digestion with FODZYME.

References

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