Oligosaccharides (Fructans and Galactans) – What’s FODMAP Diet?


Oligosaccharides are essentially carbohydrates that comprise of short chains of sugars, a length of 2 sugars to 10 sugars. There are 2 different types of oligosaccharides and they are fructans and galactans. Fructans can be accurately described as fructose polymers.

They naturally occur as storage carbohydrates of an array of vegetables such as garlic and onions, cereals and fruits. Extra sources of fructans are Fructo-oligosaccharides (popularly known as FOS) or insulin. FOS and insulin are increasingly being incorporated into foods because of their known prebiotic effects.

The small intestines in human beings is not capable of producing enzymes that can hydrolyze such fructose-fructose bonds. This is why the small intestines are unable to absorb fructans across it. Afterwards, they are delivered in the large bowel where colonic bacteria readily ferments them.

Fructans are capable of inducing abdominal symptoms, while at the same time exaggerating those that are related to lactose intolerance or fructose malabsorption. Galactans can be defined as oligosaccharides that contain chains of the galactose sugar.

Chains of galactose molecules or galacto-oligosaccharides get malabsorbed in small intestines just like fructans. People do not produce enzymes capable of hydrolyzing galactose-galactose bonds.

This is why they are readily fermented by bacteria found in the large bowel. Dietary sources of galactans include red kidney beans, chickpeas and lentils. Vegetarians normally consume large quantities of galactans due to their high intake of legumes which provide a critical protein source in their diet.

How Oligosaccharides Work In The Body

Oligosaccharides (fructans and galactans) are indigestible carbohydrates which means human beings lack the necessary enzymes to break them down inside the small intestine. This is why they arrive at the large intestine unbroken.

The large intestine has beneficial colonic bacteria that function to break down oligosaccharides (fructans and galactans) through the fermentation process into nutrients that are absorbable.

The absorbable nutrients in turn are used in the provision of energy to the body i.e. approximately two calories (kilocalories) per one gram on average. There are some breakdown products of oligosaccharides (fructans and galactans) such as short-chain fatty acids (SCFAs) that greatly benefit the lining of the large intestine.

Benefits of Oligosaccharides (Fructans and Galactans)

Oligosaccharides (fructans and galactans) are receiving increased attention in recent times due to their various roles in promoting as well as protecting human health. The following are some of the benefits of consuming oligosaccharides (fructans and galactans):

  • Most oligosaccharides are resistant to the digestion process in the human body. Therefore, they act as an extra form of dietary fiber which contributes to a digestive system that is healthy and efficient. This is why oligosaccharides (fructans and galactans) positively impact the problem of constipation.
  • Oligosaccharides such as galactans and fructans are known to greatly assist in lipid metabolism in the body.
  • These indigestible carbohydrates play a crucial role in glucose metabolism in the human body. This is important as it addresses the energy needs of your body.
  • Oligosaccharides (fructans and galactans) help in mineral absorption in the human body.
  • Fructans and galactans also have a critical role in immunomodulation.
  • Oligosaccharides (fructans and galactans) are beneficial in that they manage caloric and glucose availability.
  • Oligosaccharides (fructans and galactans) are effective prebiotics which selectively promote normal intestinal bacteria’s growth.

All the above health benefits are attributed to the fact that oligosaccharides (fructans and galactans) are resistant to digestion and are therefore a form of dietary fiber. This is because the digestive tract of human beings lacks the enzymes that are required to break down the fibers.

Risks & Side Effects

There are a good number of risks and side effects that are associated with the regular consumption of oligosaccharides (fructans and galactans). However, the notable ones include the following:


Galactans are usually mal-absorbed due to the fact that the intestine lacks the required enzymes to break down galactose bonds. This is why dietary sources rich in galactans contribute to side effects such as abdominal pain, bloating and excessive gas/ flatulence.


Fructans are also mal-absorbed as the intestine lacks the necessary enzymes to break down the fructose bond. This is the main reason why fructans cause abdominal pain, excessive gas (flatulence) and bloating side effects.

Top Oligosaccharides Sources

Fructans are usually found in wheat products, inulin, asparagus, dandelion leaves, leeks, globe artichokes, beetroot, Jerusalem artichokes, garlic, chicory and onions. Other major sources of fructans are fructooligosaccharide (FOS) and inulin, these are normally added to food so as to increase their fiber content.

Fructooligosaccharide (FOS) and inulin are also incorporated into several probiotic supplements so as to encourage the growth of bacteria which is friendly to the human gut. Galactans are normally found in soy-based products such as the common soy beans, black-eyed peas, Brussels sprout, beans, broccoli, chickpeas and lentils.

There is quite a good number of top food sources that provide oligosaccharides (fructans and galactans) to the diet, they are broken down as follows:


The vegetable sources of fructans and galactans are shallots, peas, onions, okra, leeks, garlic, fennel, cabbage, brussel sprouts, broccoli, beetroot, asparagus and artichoke.


The cereal sources of fructans and galactans include wheat and rye cereals that are usually consumed in large quantities. Common foods that contain these cereals are pasta, crackers, couscous, bread and biscuits. Wheat is considered to be the largest fructans intake amongst most people.


The legume sources of galactans as well as fructans are red kidney beans, lentils, chickpeas and baked beans.


Fruit sources of fructans and galactans comprise of white peaches, watermelon, rambutan, persimmon and even custard apple. These sources of food can be consumed to obtain oligosaccharides (galactans and fructans). It is advisable to consume the food above while fresh so as to get the most benefits from them.

Oligosaccharides (Fructans and Galactans) Conclusion

Oligosaccharides (fructans and galactans) compounds are being incorporated into numerous supplements and food products in the market today because of their plethora of health benefits. Their main advantage is that they are available in many food sources that are easily accessible and affordable to most people in society.

The incorporation of oligosaccharides (fructans and galactans) in functional foods and foods like desserts and dairy products is a step in the right direction with regard to ensuring that people fully exploit their health benefits.

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