Oligosaccharides are a type of carbohydrate naturally found in an array of plant foods.

Their ability to act as a prebiotic (food for your gut bacteria) may offer a wide range of health benefits, including a stronger immune system, a reduced appetite, and improved gut health.

Because of this, it’s now becoming popular for food makers to add oligosaccharides to foods that don’t naturally contain them, including protein bars and glucose syrup.

In this article, I’ll describe what oligosaccharides are and how they compare with polysaccharides.

I’ll also discuss which foods you can find them in, and whether these foods are truly worth adding to your diet.

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Oligosaccharides are a type of carbohydrate chain made up of three to 10 simple sugars, which are also known as monosaccharides (1).

To give you some perspective, table sugar, also called sucrose, is made up of two simple sugars joined together — glucose and fructose.

Many oligosaccharides are naturally present in common fruits and vegetables, so it’s very possible you eat them regularly.

The large majority of oligosaccharides cannot be broken down by the human digestive tract. Instead, they travel through your gut all the way to the colon, where they feed and support the growth of beneficial bacteria (2, 3).

Because of this, oligosaccharides are considered prebiotics — a source of prebiotic fiber.

Many different types of oligosaccharides exist. The most commonly known ones include (3):

  • fructooligosaccharides (FOS)
  • galactooligosaccharides (GOS)
  • human milk oligosaccharides (HMO)
  • gluco-oligosaccharides
  • lactulose-derived galactooligosaccharides (LDGOS)
  • xylooligosaccharides (XOS)
  • arabinooligosaccharides (AOS)
  • algae-derived marine oligosaccharides (ADMO)
  • pectin-derived acidic oligosaccharides (pAOS)
  • maltooligosaccharides (MOS)
  • cyclodextrins (CD)

Oligosaccharides vs. polysaccharides

Like oligosaccharides, polysaccharides also consist of a chain of monosaccharides.

However, while oligosaccharides are made up of three to 12 simple sugars, polysaccharides can contain hundreds.

Therefore, the main difference between the two is that polysaccharides are much longer chains of simple sugars than oligosaccharides.

The most commonly discussed polysaccharides include starch, cellulose, beta-glucan, pectin, xanthan, carrageenan, agar, and inulin (4).

It’s worth noting that inulin is sometimes also considered an oligosaccharide, depending on the length of its chain.

Just like oligosaccharides, some polysaccharides can act as prebiotics, improving the balance of beneficial to harmful bacteria in your gut (4).

Summary

Oligosaccharides are chains of carbohydrates that can act as prebiotics in the body, feeding your gut bacteria. Polysaccharides are also chains of carbohydrates, but they are much longer in structure than oligosaccharides.

Oligosaccharides occur naturally in some foods, and manufacturers add them to others. The foods naturally richest in oligosaccharides include (3, 5, 6):

  • Vegetables: scallions, white onions, leek, garlic, kale, red cabbage, green cabbage, broccoli, and Jerusalem artichoke
  • Fruit: nectarines, watermelon, pears, blueberries, sour cherries, mulberries, red currants, raspberries, cantaloupes, figs, and bananas
  • Grains: wheat and rye
  • Legumes: allbeans, peas, and lentils

Although other foods do naturally contain some oligosaccharides, the amount they contain is minimal, so they aren’t considered a good source of oligosaccharides, according to older research (6).

What are human milk oligosaccharides?

Oligosaccharides are also naturally present in human milk.

So far, about 15 different human milk oligosaccharides (HMOs) have been identified, and each is made up of a chain of five basic monosaccharides (7).

Infant formula contains no HMOs, but some varieties do have galactooligosaccharides (GOSs) and fructooligosaccharides (FOSs) added to them.

When they’re used in infant formula, GOSs and FOSs are meant to mimic the prebiotic composition of breast milk. Animal research suggests they may provide some similar health benefits as breast milk (7).

That said, GOS and FOS are structurally different from the oligosaccharides found in breastmilk. Moreover, breastmilk contains a larger variety of oligosaccharides (7).

Therefore, more research is needed on this topic before scientists can make strong conclusions.

Foods with added oligosaccharides

Manufacturers sometimes add oligosaccharides to other foods that don’t naturally contain them.

Inulin is the most common oligosaccharide manufacturers use. It’s often used as a replacement for fat or sugar, to modify a food’s texture, or to increase its prebiotic content (8).

Inulin is most commonly added to (8):

  • bakery foods, such as breads and cakes
  • breakfast cereals
  • dairy products
  • meat products
  • frozen desserts
  • table spreads
  • fillings
  • salad dressings
  • chocolate
  • protein bars and meal replacers

Oligossacharides can also be used as low-calorie sweeteners.

Mogrosides are one example. These are oligosaccharides extracted from monk fruit. Oligosaccharides may also be added to glucose syrups to reduce their sugar content without affecting their sweetness (9).

However, due to the current popularity of other types of low-calorie sweeteners, sweeteners made from oligosaccharides are not very common (3).

Summary

Oligosaccharides can be naturally found in human milk and various plant foods. Food manufacturers also artificially add them to packaged foods to enhance their flavor, texture, or prebiotic content.

Due to their prebiotic action, oligosaccharides have been linked to a variety of benefits.

Improved gut health

Prebiotics are a form of dietary fiber that feeds the healthy bacteria residing in your gut.

When gut bacteria feed on prebiotics, they produce a variety of beneficial substances, including short-chain fatty acids (SCFA)s. SCFAs help lower the gut pH, which in turn, limits the growth of harmful bacteria (10).

For instance, by increasing the growth of healthy bacteria in a baby’s gut, HMOs may help reduce their risk of experiencing necrotizing enterocolitis (NE) (11, 12, 13).

NE is a life-threatening illness that most commonly affects newborns. It causes inflammation in the gut, which can then progress to a full-body infection and may result in death in as many as half of cases (2).

In addition, some studies suggest that taking 3.5–20 grams of FOSs per day may help reduce symptoms of irritable bowel syndrome and Crohn’s disease — two disorders that can affect the gut in adults (14, 15).

However, other studies found that taking FOSs had no effect at all, so more research on their effects is needed.

There is also some evidence linking prebiotics to a lower risk of colon cancer. However, most of this evidence comes from animal studies, and not all human studies find similar results. Therefore, more research is needed (14, 16, 17).

Finally, oligosaccharides such as FOS and inulin can add bulk to stools and reduce the likelihood of constipation (14).

Stronger immune system

Oligosaccharides can strengthen your immune system, both directly and indirectly.

Indirectly, their prebiotic action promotes the growth of beneficial bacteria, such as Bifidobacteria and Lactobacilli, which help fight off harmful bacteria (18).

The SCFAs that are produced when bacteria ferment oligosaccharides in the colon further help reduce the growth of harmful bacteria by preventing them from attaching to the gut wall (18).

Directly, oligosaccharides help maintain the integrity of the body’s barrier membranes in the gut, lungs, and even the skin. This is thought to help protect the body from allergies and infections (18).

More specifically, a few studies suggest that consuming FOSs and GOSs may reduce the risk of developing upper respiratory infections in early childhood (15, 19).

In addition, a few other studies suggest that when infants consume HMOs they may have a lower risk of developing allergies, eczema, and asthma in early childhood (18, 20).

Some older studies further suggest that taking FOS may even improve the way your body responds to vaccines, including the influenza and measles vaccine (15).

However, more studies are needed to investigate these effects.

Other possible benefits

Oligosaccharides may provide a few additional health benefits.

  • May improve memory. A handful of studies suggest that taking FOS or GOS daily may enhance concentration, recall, and memory in adults (15).
  • May reduce risk factors for heart disease. Prebiotics — inulin in particular — have been linked to lower total cholesterol and triglyceride levels in some but not all people (15).
  • May increase nutrient absorption. Some studies suggest that prebiotics may help increase the absorption of calcium, magnesium, and iron (14, 21).
  • May reduce appetite. Animal and human studies suggest that prebiotics may increase levels of hormones that signal fullness, thereby reducing hunger (22).

Although all these potential benefits are promising, research on them remains conflicting. Therefore, more studies are needed before researchers can make strong conclusions.

Summary

Oligosaccharides have several potential health benefits, though more research is needed on these. Possible benefits include improved immunity, gut health, nutrient absorption, and memory, and reduced appetite and total cholesterol.

Oligosaccharides are generally considered safe and free of severe side effects.

That said, the large majority of oligosaccharides will ferment in the colon, which can cause bloating, cramping, gas, or diarrhea in some people (15).

If you are currently experiencing these symptoms, try reducing the amount or frequency of oligosaccharide-rich foods you eat and see if your symptoms improve (15).

One way of doing this is to follow a low-FODMAP diet, which contains lower amounts of oligosaccharides and other non-digestible short-chain carbohydrates that can cause digestive issues.

To minimize symptoms in the future, try increasing the amount of oligosaccharide-rich foods in your diet gradually.

Summarize

Oligosaccharides are generally considered safe but can cause bloating, cramping, gas, or diarrhea in some people. To minimize symptoms, increase your intake of oligosaccharide-rich foods gradually.

Oligosaccharides are a type of carbohydrate with prebiotic properties. Because of this, they may bring health benefits, such as an improved digestion and gut health.

They also appear to increase the body’s defence against upper respiratory infections, eczema, and allergies, although more research is needed to investigate this and other potential benefits.

Keep in mind that most oligosaccharides ferment in the colon, which may cause bloating, gas, cramping, and diarrhea in some people.

To minimize your risk of experiencing these side effects, you may want to increase your intake of oligosaccharide-rich foods gradually rather than all at once.

Just one thing

Try this today: Substitute meat, chicken, or fish with beans, peas, and lentils in a meal. Doing this a few times each week is a great way to gradually increase your intake of oligosaccharides.

To further minimize gas and bloating, make sure to thoroughly rinse canned legumes prior to adding them to your meals, or change the water a few times when cooking them from scratch.