What the FODMAP is a FODMAP?

IBS FODMAP dietitian NW calgary

Have you heard of FODMAPs or the Low FODMAP Diet yet? For most of us, when we first come across the term FODMAP, we may quietly ask ourselves “What the FODMAP is a FODMAP? Is it another fad diet making the rounds or some sort of ‘super food’ I should be eating?” I’m here to tell you that it’s not another fad diet (thank goodness, right?) and it certainly isn’t a new trendy food making the rounds in the posh wellness scene right now.

FODMAPs are actually components found in many of the foods that we eat - in fruits, vegetables, grains, nuts, legumes, dairy, as well as in a number of other processed foods. The significance of these FODMAPs is that for those who struggle with Irritable Bowel Syndrome (IBS) they can trigger mild to severe symptoms including abdominal pain, bloating, distention, gas, diarrhea and constipation.

The Low FODMAP Diet is a diet protocol designed to help those with IBS identify which FODMAPs are causing gastrointestinal symptoms. Evidence shows that the Low FODMAP Diet is effective in improving symptoms in 70% of people with IBS. As well, a systematic review and meta-analysis found that the Low FODMAP Diet is able to reduce symptom severity and improved quality of life of those with IBS. 



FODMAP is actually an acronym that stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols. To make it easy to talk about these components as a group, they are collectively referred to as FODMAPs. It sort of makes it easier, doesn’t it? Some of those names are quite a mouthful.

FODMAPs are small, poorly absorbed carbohydrates which either attract water to the small intestine and/or are fermented by the bacteria living in the large intestine. These actions of FODMAPs within the digestive tract are what cause symptoms for many people with IBS.

But wait...if FODMAPs are in a huge number of foods we eat and they cause these symptoms, then shouldn’t we all be avoiding them? The answer to this is ‘no’. FODMAPs do not cause symptoms in everyone and you do not need to avoid them if they don’t cause you grief. You don’t really even need to avoid them if they cause tolerable symptoms, like a bit of gas or mild bloating. It’s when they cause significant enough symptoms to negatively affect your daily life that the Low FODMAP Diet may be something to be considered.

While we don’t know the exact cause of IBS, we do know that those with IBS have digestive tracts that are more sensitive to these components. Tolerance level to these FODMAP components vary, even between those with IBS. Some people’s tolerance for FODMAPs is quite low, while other people can handle a bit more before symptoms arise.

What’s important to keep in mind is that FODMAPs don’t cause any damage to your gut.  There is no physical damage happening to your intestines, unlike what happens to someone with celiac disease when they consume gluten (gluten physically damages the small intestine). The reaction to eating FODMAPs for people with IBS may be unpleasant, or even painful but their consumption does not cause any damage to the body.

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By now, you’re probably wondering where these FODMAPs I’ve been speaking of are found. The general answer is that they are naturally found in a number of different foods including fruits, vegetables, nuts, grains, legumes, and dairy. There are also some FODMAPs that are added to processed foods. That covers a lot of different foods, doesn’t it?

For a more specific answer, I've listed the FODMAP subgroups below and highlighted a few foods in each group. Please note that these lists of foods high in FODMAPs are not complete lists. For more detailed information regarding the FODMAP content of foods - download the Monash FODMAP app or see a Registered Dietitian.



There are two main groups of oligosaccharides in the Low FODMAP Diet, fructans and galacto-oligosaccharides (or GOS, for short). Fructans are found in a number of foods including wheat, barley, rye, onion, garlic, grapefruit, nectarines, and watermelon. Galacto-oligosaccharide are found in legumes (like kidney beans, black beans and soybeans), bitter melons, peas, cashews, and pistachios.

Fructans and GOS are not able to be absorbed as our body does not contain the enzymes needed to break them down. This means that both fructans and GOS will pass on through to the large intestine where they are fermented by bacteria to produce gas. This is true for both those with and without IBS. In sensitive individuals (i.e. those with IBS) the production of gas will cause bloating, distention and altered bowel habits (diarrhea or constipation).

One thing to note is that both fructans and GOS are important for our digestive health as they act as prebiotics, or food, for the beneficial bacteria within our gut. So while they do cause symptoms in some people with IBS, at least some intake of foods with these FODMAPs is important for a healthy gut environment.





The ‘D’ in FODMAP stands for disaccharide, which in this case refers to lactose. Lactose is a carbohydrate made up of two sugar units (glucose and galactose) and is found in dairy products, including milk, yogurt, ice cream, sour cream and condensed milk. 

Lactose is digested by the lactase enzyme in the small intestine, however, many people are lacking this enzyme and are unable to tolerate much in the way of dairy products. Lactose intolerance is not, however, specific to IBS. It is equally common in those with and without IBS.




Fructose, and more specifically excess fructose, has been implicated in causing symptoms in those with IBS. Let me explain further. If the fructose concentration of a food is equal or lesser than the concentration of glucose, it is generally well tolerated. However, if fructose is present in a greater concentration than glucose, it can cause digestive trouble. This is why we specify that excess fructose, and not just fructose itself is something to avoid on the low FODMAP diet. 

If you are curious why - it’s all about how it gets absorbed. When fructose exceeds glucose in the small intestine, absorption switches to a slower, less efficient method. With a bunch of fructose hanging around waiting to get absorbed, it attracts water into the small intestine and because absorption is slow and inefficient, a portion of fructose will travel to the colon to get fermented by bacteria. These actions once again cause abdominal pain, bloating, distention, gas, and altered bowel habits (often times diarrhea).

Fructose is found in fruit (and some vegetables). Fruits and veggies with excess fructose include apples, cherries, figs, mangos, pears, asparagus, sugar snap peas, and Jerusalem artichokes. Sweeteners such as honey and high fructose corn syrup are also sources of excess fructose.



Polyols, also known as sugar alcohols, make up the last FODMAP subgroup. The polyols that cause many of our digestive woes are sorbitol and mannitol. Similar to excess fructose, the absorption of sorbitol and mannitol is a slow and inefficient process. If present too long in the small intestine they will draw water into its lumen, while any of the polyols not absorbed will be fermented in the colon causing symptoms in those with IBS. 

Sorbitol is found in sweet corn, avocados, apples, blackberries, pears, lychee and stone fruit (apricots, peaches and plums). Mannitol is found in cauliflower, mushrooms and snow peas. In addition to sorbitol and mannitol, there are other polyols that are added to foods as sugar-free sweeteners including maltitol, xylitol, and isomalt. These are often found in sugar-free candy and chewing gum and should also be avoided on the low FODMAP diet.


The Low FODMAP diet has three phases.

First is an elimination phase in which all of these potentially offending FODMAP components are removed. This stage lasts anywhere from 2-6 weeks (more realistically it’s 4-6 weeks).

This is followed by a re-challenge phase where each FODMAP subgroup is systematically added back into the diet to identify triggers. Each challenge is done over a 3-6 day period. In between each food challenge, the low FODMAP diet is resumed. Even if some high FODMAP foods are found to be tolerated they are not added back into the diet until the final stage of the diet. This whole process should take 6-8 weeks.

The final or maintenance stage is called the adapted FODMAP phase in which only FODMAP foods which cause symptoms are restricted or limited to tolerable portions (this is different for everyone). The final goal of this diet is to have good symptom control and to have the least restrictive diet as possible. It's important to note that even if certain subgroups are found not to be tolerated during the re-challenge phase, it is recommended to challenge foods every 6 months as individual tolerance to foods can change.

If you want to learn more, I suggest you connect with a Registered Dietitian with experience in the Low FODMAP Diet.

Want to read more about the low FODMAP diet? Check out 10 Things This Dietitian Learned Doing the Low FODMAP Diet