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What Are Oligosaccharides? Learn All About the “O” in FODMAP!

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Let’s Talk About the “O” in FODMAP

The “O” in FODMAP stands for oligosaccharides (sometimes referred to as “Oligos”) — a category that comprises both fructans and galacto-oligosaccharides (GOS). This is a large and diverse category, populated with items from most of the major food groups.

FODMAP graphic highlighting Oligosaccharides

The Chemistry of the “O” in FODMAP

Oligosaccharides, for our purposes, are molecules that typically contain 3 to 10 linked monosaccharide units, or “simple sugars.” In the case of fructans these monosaccharides are fructose, and in the case of GOS they are galactose.

Oligosaccharides consisting of up to 60 monosaccharide units are often referred to as polysaccharides, and according to Dr. Emma Halmos and Dr. Peter Gibson of Monash University, these longer chain molecules, such as inulin, behave like FODMAPs in their ability to be fermented and to induce gut symptoms.

Symptoms of Oligo Excess

Oligosaccharides are not absorbed by humans whether they have irritable bowel syndrome (IBS) or not because we lack the enzymes needed to break the bonds between the chains that make up these molecules. This is why eating beans, which are high in Oligos, often results in flatulence.

Instead of being absorbed and used as fuel, oligosaccharides travel through the small intestine to the large intestine where they are fermented by bacteria.

This is an entirely normal process, but for those with IBS, the gas that accumulates as a by-product of bacterial fermentation pushes on the walls of the large intestine, causing pain, abdominal bloating, flatulence, and altered motility (diarrhea and/or constipation). These symptoms can be mild and intermittent or severe and persistent enough to have a significant negative impact on a person’s quality of life.

Food sources of Oligosaccharides

Food Sources of Oligosaccharides

Oligosaccharides can be found in a wide array of food, but they are most heavily concentrated in breads, cereals, pasta, and legumes. In fact, if you scroll through the Monash University FODMAP Diet appyou will find that nearly every item in those categories contains fructans, GOS, or both.

Nuts and vegetables are also well represented in this group, but the head-scratcher for most people is fruit, which we tend to associate with the sweeter (“M” and “P”) FODMAP categories. 

List of foods that have oligosaccharides

Oligosaccharides Are Water-Soluble

An important thing to understand about oligosaccharides is that they are water-soluble. This means that they will leach out into soup and other liquids even if the oligos food source (like garlic or onion) is removed.

Luckily, there are some workarounds for this, as you will see from our FODMAP Everyday® articles and recipes. Be sure to read Not All Low FODMAP Garlic-Infused Oil is Created Equal, and also check out our recipes for Low FODMAP Garlic-Infused Oil and Low FODMAP Onion-Infused Oil. 

Oligosaccharides are not oil-soluble, which is what allows us to pack these oils with onion and garlic flavor.

Health Benefits of Oligos

Fructans and GOS can act as prebiotics – compounds in food that stimulate the growth and activity of beneficial gut bacteria, in particular, bifidobacteria and lactobacilli.

Prebiotics have been shown to:
    • Alleviate infectious and antibiotic-associated diarrhea
    • Help protect against colon cancer
    • Increase the bioavailability and uptake of calcium and magnesium
    • Promote satiety and weight loss

Bottom Line

It’s important to remember that many high FODMAP foods – especially those in the “O” category – are extremely healthy and should not be eliminated entirely in the long run.

That’s why it is so vital that you test your sensitivity to items rich in fructans and GOS during the Challenge and Integration Phases of the low FODMAP diet.

Once you determine your personal tolerance level, you’ll find that you are able to incorporate small servings of foods that contain these FODMAPs into your daily diet.

Be sure to read all of the other articles in this series!

What Are FODMAPs?

The Low FODMAP Diet

Is the Low FODMAP Diet Right For Me?

What are Disaccharides? 

What are Monosaccharides?


What are Polyols?

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