If you've ever wondered what oligosaccharides are, you're not alone. These short-chain carbohydrates, made up of simple sugars, play an important role in nutrition and digestion. Found naturally in many plant-based foods—like onions, garlic, beans, and whole grains—oligosaccharides are not only a source of fiber, but also fuel for your good gut bacteria.

However, while some people can tolerate oligosaccharides like fructans and galacto-oligosaccharides in their diet, they can cause digestive discomfort for people with an oligosaccharide intolerance, which includes many people with irritable bowel syndrome (IBS). Read on to learn the basics of oligosaccharides, where they're found, and tips for managing their effects on your gut.

What Are Oligosaccharides?

Oligosaccharides are short-chain carbs made up of sugar molecules. Before diving into the different oligosaccharides, it's important to understand some basic biochemistry (stick with us!). Carbohydrates are made up of tiny building blocks of sugars called "monosaccharide units." Each sugar is like a brick, and when you stack them together in different ways, you get different kinds of carbs. There are three main types of sugars: glucose, fructose, and galactose.

The basics of oligosaccharides

There are several types of oligosaccharides, with the most common being fructans, galacto-oligosaccharides (GOS), raffinose, and stachyose.

Fructans are chains of fructose molecules, often with glucose at one end. Short fructans, called fructo-oligosaccharides (FOS), have 2-9 fructose units, while fructans made of 10 or more fructose units are called inulins. Fructans are found in foods like onions, garlic, wheat, and certain fruits like bananas. Inulin-type fructans are commonly used as a sweetener or fiber-booster in processed foods. Fructan intolerance happens when a person is unable to tolerate fructans in their diet.

GOS are made of chains of galactose. They're found in lentils, chickpeas, kidney beans, cashews, and pistachios. They're also naturally found in human breast milk. 

Raffinose is found in cruciferous vegetables, legumes, and tubers. It's made of galactose, glucose, and fructose joined together. 

Stachyose is made of two galactose units joined to glucose and fructose. It's found in legumes like beans, chickpeas, and lentils.

How oligosaccharides are classified within carbohydrates

Oligosaccharides are a subcategory of carbs. Carbohydrates are divided into three main groups based on how many individual sugar units they contain: sugars (monosaccharides and disaccharides), oligosaccharides, and polysaccharides.

Monosaccharides are single sugar units (glucose, fructose, or galactose), while disaccharides are two sugars linked together (like sucrose and lactose).

In contrast, oligosaccharides are short chains of 3-10 sugar units (like fructans and GOS), while polysaccharides are longer chains of ten or more sugar units (like starch and cellulose).

Common Sources of Oligosaccharides

Oligosaccharides are present in a lot of plant-based foods, but you can also find them hiding in many processed foods. Here are some of the most common food sources of oligosaccharides:

Foods high in oligosaccharides

Galacto-oligosaccharides (GOS):

  • Lentils
  • Chickpeas
  • Black beans
  • Kidney beans
  • Pinto beans
  • Navy beans
  • Fava beans
  • Soy products (such as non-firm tofu, certain types of soy milk, and edamame)

Fructans:

  • Onions
  • Garlic
  • Leeks
  • Shallots
  • Scallions (the white part)
  • Asparagus
  • Artichokes
  • Bananas
  • Watermelon
  • Wheat (bread, pasta, etc.)
  • Rye
  • Barley
  • Spelt
  • Red kidney beans
  • Navy beans
  • Black beans
  • Lima beans
  • Pistachios
  • Cashews
  • Chicory root
  • Jerusalem artichokes
  • Dandelion root
  • Added as a fiber supplement in some breads, cereals, and protein bars

Raffinose and stachyose:

  • Kidney beans
  • Black beans
  • Navy beans
  • Soybeans
  • Lentils
  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Asparagus

Hidden sources of oligosaccharides in everyday diets

In addition to the naturally present fructans, GOS, raffinose, and stachyose in several commonly eaten whole foods, there are many hidden sources of oligosaccharides. Some of the main hidden sources include:

  • Supplements: Many prebiotic fiber supplements contain oligosaccharides like GOS and fructans (like inulin).
  • Meal replacements and shakes: Prebiotic fibers like GOS and fructans are often added for gut health benefits or as sweeteners.
  • Soups and stocks: Broth or stock bases made with onions and garlic contain fructans.

The best way to identify hidden oligosaccharides is to read food labels. Look for terms like "chicory root fiber," "inulin," "prebiotics," "soy," "pea protein," ‘Fructooligosaccharides (FOS),” and "added fiber."

Oligosaccharides and Digestive Health

Oligosaccharides play a key role in the health of the digestive system because they act as prebiotics—food for beneficial gut bacteria. These beneficial gut microbes ferment the oligosaccharides in the large intestine, producing short-chain fatty acids (SCFAs). 

SCFAs have several important roles in the body, including fueling our colon cells, nourishing the gut lining and reducing inflammation. Some research even suggests that SCFAs can reduce the risk of colon cancer. Overall, a balanced gut microbiota supported by oligosaccharides helps digestion, enhances immune function, and protects against harmful microbes.

Why some people experience oligosaccharide intolerance

While most healthy people can tolerate oligosaccharides like fructans and galacto-oligosaccharides without trouble, others experience oligosaccharide intolerance because these carbohydrates are not fully digested in the small intestine. For example, only about 5-15% of fructans are absorbed in the small intestine. 

Due to their poor absorption, when oligosaccharides reach the large intestine they get fermented by the gut microbes. This can cause IBS symptoms like gas, bloating, and discomfort.

What Is Oligosaccharides Intolerance?

Remember how oligosaccharides aren't broken down in the small intestine during digestion? This happens because humans lack the enzymes needed to break the bonds between the sugar molecules that make up oligosaccharides. As a result, the gut microbes in the large intestine ferment them, producing gas. For certain people, such as those with IBS, this can cause abdominal pain and bloating.

Common symptoms of intolerance

Common symptoms of oligosaccharide intolerance include:

  • Gas
  • Bloating
  • Abdominal pain or cramping
  • Diarrhea
  • Constipation
  • Excessive flatulence
  • Discomfort after eating certain foods

How to identify if oligosaccharides are causing your symptoms

There are several ways to identify if oligosaccharides are causing your symptoms. The first is to keep a food and symptom journal. Write down everything you eat and drink, plus any symptoms you experience. Then, you can look back in your food journal to see if there are any correlations between the foods you've eaten and your symptoms.

Another way of identifying oligosaccharide intolerance is a temporary elimination diet like the low-FODMAP diet. Removing high oligosaccharide foods from your diet for a few weeks and systematically reintroducing them can help pinpoint the cause of your symptoms.

Both methods of identifying an oligosaccharide intolerance are best done under the supervision of a dietitian. They will take a medical history to ensure there are no reasons that eliminating FODMAPs may be contraindicated for you. Working with a dietitian can also help ensure you correctly identify trigger foods without unnecessarily restricting your diet. 

Managing Oligosaccharides Intolerance

Reducing your intake of oligosaccharides may help minimize digestive symptoms like gas, bloating, and abdominal discomfort. However, reducing oligosaccharide intake in the long term may negatively affect your gut microbiota since these non-digestible carbohydrates keep your good gut microbes healthy. 

Dietary adjustments to reduce symptoms

Here are some tips for reducing your intake of oligosaccharides:

  • Avoid or reduce foods like onions, garlic, beans, lentils, and certain cruciferous vegetables (like Brussels sprouts and cabbage).
  • Use garlic-infused oils, which provide flavor without the oligosaccharides.
  • Eat canned legumes, as the canning process leaches oligosaccharides from the legumes (make sure to drain and rinse thoroughly before eating).
  • Use digestive enzymes, which can break down the oligosaccharides your body can't.

Low-oligosaccharide food alternatives

Fortunately, you can include many low-oligosaccharide food alternatives in your diet while minimizing your oligosaccharide intake. Here are some suggestions:

  • Vegetables: Carrots, bell peppers, spinach, eggplant, cucumber, green beans, broccoli, and lettuce.
  • Legumes: Firm tofu or canned lentils or chickpeas (rinse well to reduce GOS).
  • Flavor enhancers: Fresh herbs, chives, garlic-infused olive oil, and ginger instead of garlic or onion.
  • Grains: Rice, quinoa, oats, sourdough spelt bread, and buckwheat.
  • Nuts and seeds: Macadamia nuts, pecans, walnuts, and hazelnuts
  • Fiber supplements: Partially hydrolyzed guar gum (PHGG), acacia fiber, and psyllium husk.

Oligosaccharides and the Low-FODMAP Diet

Oligosaccharides are types of FODMAP — the "O" in the acronym. FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols. When high-FODMAP foods are eaten, the carbohydrates are fermented in the colon, producing symptoms like gas and bloating in susceptible individuals, such as those with IBS. This is known as FODMAP intolerance.

How oligosaccharides fit into the FODMAP framework

During the low-FODMAP diet's elimination phase, foods high in oligosaccharides (like beans, garlic, onions, and wheat) are reduced to help manage digestive discomfort. However, the low-FODMAP diet should not be followed long-term, and reintroducing eliminated foods to determine triggers is just as important as the elimination phase.

Digestive Support for Oligosaccharides Intolerance

As previously mentioned, eliminating oligosaccharides permanently isn't a good idea because oligosaccharides act as fuel for your good gut bacteria. 

Digestive enzymes, such as FODZYME, can play an important role in managing oligosaccharide intolerance and reducing digestive discomfort. These enzymes help break down oligosaccharides in foods before they reach the large intestine, which reduces the amount of fermentation in the colon. In other words, digestive enzymes make it easier for the body to process oligosaccharides without triggering unpleasant gut symptoms.

The role of digestive enzymes in managing symptoms

If you struggle with oligosaccharide intolerance, digestive enzymes like FODZYME can help. FODZYME contains three enzymes, two of which break down oligosaccharides (the other enzyme helps with lactose intolerance). Learn how FODZYME can help break down oligosaccharides for easier digestion and improve your gut health today.