What are fermentable carbohydrates?

What are fermentable carbohydrates?


Fermentable carbohydrates are a type of dietary carbohydrates that can be broken down by bacteria in the gut through a process called fermentation. This process produces various byproducts, including short-chain fatty acids, gases, and other compounds. Fermentable carbohydrates play a crucial role in our digestive system and have been the subject of extensive research due to their impact on gut health and overall well-being.

Types of Fermentable Carbohydrates

There are several types of fermentable carbohydrates, including:

Oligosaccharides: Oligosaccharides are short chains of sugar molecules. They can be found in foods such as beans, lentils, onions, and garlic. The most well-known type of oligosaccharides is called fructooligosaccharides (FOS), which can act as a prebiotic, promoting the growth of beneficial bacteria in the gut.

Fructans: Fructans are a type of carbohydrate made up of fructose molecules. They are commonly found in wheat, rye, barley, and some fruits and vegetables. Fructans can be difficult to digest for some individuals, leading to symptoms such as bloating and gas.

Lactose: Lactose is the sugar found in milk and dairy products. Some individuals have difficulty digesting lactose due to a deficiency of the enzyme lactase, which is responsible for breaking down lactose. This can result in lactose intolerance and symptoms such as bloating, diarrhea, and abdominal pain.

Polyols: Polyols, also known as sugar alcohols, are naturally occurring carbohydrates found in certain fruits and vegetables, as well as in some artificial sweeteners. Examples of polyols include sorbitol, mannitol, and xylitol. Polyols can have a laxative effect and may cause bloating and diarrhea in some individuals.

Role in Gut Health

Fermentable carbohydrates play a crucial role in maintaining a healthy gut. When these carbohydrates reach the large intestine undigested, they provide a source of nutrition for the beneficial bacteria residing in our gut, known as the gut microbiota. These bacteria ferment the carbohydrates, producing short-chain fatty acids, such as butyrate, acetate, and propionate.

Short-chain fatty acids are important for gut health as they provide energy for the cells lining the colon and help maintain a healthy gut barrier. They also have anti-inflammatory properties and can modulate the immune system. Additionally, short-chain fatty acids play a role in regulating appetite and metabolism.

Effects on Digestive Symptoms

For some individuals, fermentable carbohydrates can cause digestive symptoms such as bloating, gas, abdominal pain, and changes in bowel habits. This condition is known as irritable bowel syndrome (IBS) or functional gastrointestinal disorders (FGIDs). The symptoms are believed to be caused by the fermentation of these carbohydrates in the gut, leading to an imbalance in the gut microbiota and increased gas production.

A low fermentable carbohydrate diet, known as the low FODMAP diet, has been developed to help manage these symptoms. FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols. This diet involves restricting high FODMAP foods for a period of time and then gradually reintroducing them to identify specific triggers for symptoms.


Fermentable carbohydrates are a diverse group of dietary carbohydrates that can be fermented by bacteria in the gut. They play a crucial role in gut health and can have both positive and negative effects on digestive symptoms. Understanding the impact of fermentable carbohydrates on the gut microbiota and individual tolerance is essential for managing digestive health and overall well-being.


– Monash University. (n.d.). The Low FODMAP Diet. Retrieved from https://www.monashfodmap.com/
– Halmos, E. P., Power, V. A., Shepherd, S. J., Gibson, P. R., & Muir, J. G. (2014). A diet low in FODMAPs reduces symptoms in patients with irritable bowel syndrome and a probiotic restores Bifidobacterium species: a randomized controlled trial. Gastroenterology, 146(1), 67-75.