The Low FODMAP Diet: All About Oligosaccharides

Are you following the low FODMAP diet to manage your irritable bowel syndrome (IBS) symptoms? If so, you may be wondering what all those letters stand for. This article focuses on the "O" in FODMAP. The "O" in FODMAP stands for oligosaccharides. It includes fructans and galactooligosaccharides (GOS).

I’ll review why fructans and GOS can affect IBS symptoms, review which foods have them, and give some information about why it is important to include them in your diet.

What are oligosaccharides?

Oligosaccharides are carbohydrate molecules that usually contain between 3 and 10 linked monosaccharide or "simple sugar" units.1

Fructans are made up of the simple sugar fructose, while GOS involves the simple sugar galactose. Inulin is a special type of oligosaccharide that contains up to 60 linked fructose units.2

Oligosaccharides and digestion

Regardless of whether they have IBS, humans are not able to digest oligosaccharides because we don’t make the enzyme needed to break the chemical bonds between the simple sugar units.1

Since they are not digested, oligosaccharides pass into the large intestine undigested. There, your gut bacteria feed on them. What follows is gas and bloating.1

For someone without IBS, this is not an issue, and the gas is passed normally. But for people with IBS, who have extra sensitive guts (also known as visceral hypersensitivity), this can cause a great deal of discomfort, bloating, and changes in digestion.3

What foods contain oligosaccharides?

According to the Monash University FODMAP app, oligosaccharides are commonly found in:

  • Bread
  • Cereals
  • Pasta
  • Legumes (like beans and lentils)
  • Nuts
  • Onions
  • Garlic

It’s important to note that oligosaccharides dissolve in water. This means that if you are following the elimination phase of the low FODMAP diet, you can’t add a high oligosaccharide food (like a whole garlic clove) to a recipe and then remove it before eating. The oligosaccharides will leech into the liquids in your meal.4

However, the oligosaccharides do not dissolve in oil. This means that you can make infused oil using onions and garlic. The flavor of the onions and garlic will transfer to the oil, while the FODMAPs will not. This is a handy trick for people following the low FODMAP diet and missing onions and garlic.4

Health benefits of oligosaccharides

Oligosaccharides are prebiotics. According to the International Scientific Association for Probiotics and Prebiotics (ISAPP), a prebiotic is "a substrate that is selectively utilized by host microorganisms conferring a health benefit."5

In other words, prebiotics are food for your gut microbes. Breaking down prebiotics has benefits for your body. Your body produces molecules called short-chain fatty acids (SCFAs), which act as a fuel source for your gut cells and impact the immune system. Prebiotics also promote the growth of good bacteria and reduce the growth of bad bacteria in your gut.6

It is important not to avoid oligosaccharides in the long term. Once you have finished the elimination phase of the low FODMAP diet, reintroduce the foods you were avoiding gradually and assess your tolerance to them.7

After learning which types of FODMAPs your body can handle, you can include them in your diet. You may find that you are able to tolerate small amounts of oligosaccharides, which will contribute to your overall gut health.7

Final thoughts

Oligosaccharides are a type of FODMAP that are commonly found in foods like bread, nuts, onions, and garlic. While they are eliminated during the elimination phase of the low FODMAP diet, it is important to reintroduce them, if possible, into your diet because you need them for overall gut health.

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