The term FODMAP was coined to give a name to the 4 categories of short-chain carbohydrates which all irritate the gut, one way or another.

In order to properly understand the FODMAP diet, the ways it works and why not sticking to the diet causes so many symptoms, we need to begin by understanding what the various parts of the word FODMAP mean. Today we’re taking a closer look at the meaning behind the second letter of the word FODMAP: oligosaccharides.

In order to understand how oligosaccharides irritates the gut, we need to take a closer look at both monosaccharides and disaccharides, what they are and how the human body digests them. I highly recommend reading our article about monosaccharides (click here) and checking out our article about disaccharides thereafter (click here). But in case you missed it:

Monosaccharides & disaccharides

Monosaccharides are the basic building blocks from which all carbohydrates are built.
Monosaccharides are the category for which the 4th letter of the word FODMAP stands. For more detailed information about monosaccharides, click here.

Fructose is one of many monosaccharides, however, it is the only monosaccharide that causes trouble in the digestive system of individuals with Irritable Bowel Syndrome (IBS) and Small Intestinal Bacterial Overgrowth (SIBO). Click here for more detailed information about fructose.

When two monosaccharides are bonded to one another, by a so-called glycosidic linkage, they form a disaccharide.
Disaccharides are the category for which the 3rd letter of the word FODMAP stands. For more detailed information about disaccharides, click here.

Lactose is one of many disaccharides, however, it is the only disaccharide that causes trouble in the digestive system of individuals with Irritable Bowel Syndrome (IBS) and Small Intestinal Bacterial Overgrowth (SIBO). Click here for more detailed information about lactose.

Oligosaccharides

When three to ten monosaccharides are bonded to one another, by a glycosidic linkage, they form an oligosaccharide. There are a variety of different oligosaccharides, however, there are only two oligosaccharides which cause trouble in the digestive system of individuals with Irritable Bowel Syndrome (IBS) and Small Intestinal Bacterial Overgrowth (SIBO), namely:
1. Galactoligosaccharides;
2. Fructans

Digestive enzymes

In order to digest food and use it as fuel, the human body needs to break down any and all foods, with the help of digestive enzymes.

Oligosaccharides made from glucose are broken down into glucose subunits by an enzyme called “pancreatic amylase”. However, that enzyme is unfortunately not able to break down every single type of oligosaccharides. The enzymes needed to break down the oligosaccharides: galactoligosaccharide and fructan are not present in the human body. Therefore, these oligosaccharides move through the gut completely undigested.

Just like with undigested fructose and undigested lactose, undigested fructans and undigested galactoligosaccharides too get transported into the larger intestine. In the larger intestine these undigested bits of food then get fermented by the gut bacteria, but the question remains: why do these short chain carbohydrates – called FODMAP’s – cause so many problems?

Why oligosaccharide cause so many symptoms

To answer that question one must understand what the first letter of the term FODMAP stands for: fermentation. That chemical process is precisely what causes your symptoms. But what exactly does fermentation do?

‘You may have heard of fermentation in connection with yeast. Yeast performs fermentation to produce energy by converting sugar into alcohol and carbon dioxide. Fermentation turns fruit juices into wine and grain mash into beer or whiskey.

The carbon dioxide produced by fermentation makes the bubbles in beer and some kinds of wine, and causes bread to rise.

Bacteria in our colon extract energy by fermenting carbohydrates, but the fermentation process also yields gasses. In the case of glucose [the monosaccharide into which fructose needs to be broken down, in order to digest it] the fermentation process leads to hydrogen, carbon dioxide and methane.

In addition to accumulating gasses, polyols, monosaccharides, disaccharides and small undigested remnants of oligosaccharides cause what is called an osmotic effect.’ 1

Osmosis

Osmosis refers to the movement of water molecules from a solution with many water molecules, to a solution with little water molecules.

In the digestive system, osmosis occurs as the result of compounds like (1) salt, (2) poorly digested or (3) completely undigested remnants of FODMAP’s. These three compounds all attract water like a magnet, resulting in a more watery stool than it would have been without the occurrence of osmosis.

This osmotic reaction leads to bloating, gas, diarrhea and pain. Thus osmosis – also known as an osmotic reaction – is an important process to understand, to gain a better understanding of where your symptoms come from.

In addition to that, these bodily responses that occur as a result of fermentation – can lead to symptoms like flatulence and nausea.

Stating the obvious: osmosis – and the implications it leads to – is literally and figuratively quite shit to experience. Pun intended.

Although some people can’t consume even the smallest bit oligosaccharides without resulting in symptoms, most individuals can. Generally humans are able to tolerate small amounts of fructans and galactoligosaccharides, without resulting in symptoms, just not massive plates filled with foods high in these FODMAP categories.