The Low FODMAP Diet Approach: What are FODMAPs?

What are FODMAPs?

There are several different types of short-chain carbohydrates that make up the FODMAP family. Some foods containing these are:


These comprise fructans (fructo-oligosaccharides or FOS), which are made up of short chains of fructose with glucose on the end, and galacto-oligosaccharides (GOS), which are short chains of sucrose and galactose units. These oligosaccharides are unable to be digested as humans do not have enzymes to break them down. Hence, they are not absorbed in the small intestine by anyone and, therefore, can cause problems for all patients with irritable bowel syndrome (IBS).


These are sugar alcohols and the most common ones in the diet are sorbitol and mannitol. Because their absorption is slow across the intestinal barrier, only about one-third of what is consumed is actually absorbed. Because of this, sorbitol is often used as a low-calorie sweetener in “sugar-free” products, especially candies and chewing gum.

Excess fructose

Fructose is a simple sugar and requires no digestion. However, the absorption of fructose relies on the activity of sugar transporters that are located in the wall of the small intestine. Fructose is absorbed in two different ways, all depending on how much glucose is present in a food.

Firstly, if glucose is present in equal or greater amounts than fructose, the glucose seems to piggyback the fructose across the small intestinal barrier.

Secondly, if fructose is in excess of glucose, it requires an alternative absorption method. This method of absorption is impaired in some individuals and is the cause of fructose malabsorption. Around 30–40% of healthy and IBS individuals malabsorb excess fructose.


Lactose is a disaccharide, made up of two sugar units. It needs to be broken down into individual sugar units by an enzyme called lactase prior to absorption. Hence, lactose is only a FODMAP when there are insufficient levels of lactase, which can be influenced by factors such as genetics, ethnicity (almost 100% of Asians and American Indians have low lactase levels), and many gut disorders.

Adapted from IFFGD Publication #251 by CK Yao, Jessica Biesiekierski, Sue Shepherd, Peter Gibson, Eastern Health Clinical School, Monash University, Box Hill Hospital, Melbourne, Australia.
Last modified on September 15, 2014, at 12:52:05 PM

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