What is the FODMAP Diet and How Can It Help Reduce IBS Symptoms?


FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, which are all fancy names for different types of carbohydrates that exist in certain foods.

In a patient with healthy gut function, many of these carbohydrates are beneficial and absorbed well, acting as prebiotics that stimulate the proliferation of healthy gut microbes. In patients with inflammatory digestive disorders such as irritable bowel syndrome (IBS), however, through various mechanisms, they can exacerbate symptoms like gas, bloating, diarrhea, constipation, gut pain, cramping, and even reflux. 

Therefore, removing these common food triggers for IBS patients can help minimise digestive symptoms in response to certain food triggers.

Inflammatory reactions to these FODMAP foods as a result of decreased digestion/absorption, can also manifest in other body systems as well, therefore removing them can help improve other symptoms that go beyond the digestive tract. 

Due to multi-faceted causes, patients with IBS have inflammation in the small intestine due to imbalances of good and bad bacteria. This imbalance is called small intestinal bacterial overgrowth or SIBO for short. SIBO is thought to be a main underlying driver of IBS. SIBO is a driving factor behind a lot of IBS patient’s digestive symptoms as it leads to a decreased digestion and absorption of certain foods, which then causes digestive symptoms due to excessive fermentation and gas production by gut bacteria of unabsorbed food. Inflammation in the gut lining results from poor gut bacteria balance.

FODMAP foods are the most common triggers of digestive symptoms for IBS/SIBO patients because they seem to have the most trouble digesting and absorbing these foods due to inflammation in their gut lining from bacterial overgrowth that release inflammatory molecules that disrupt normal digestive processes. . 

Unfortunately, no studies to date have looked at the effect of a low-FODMAP diet on long-term SIBO and IBS outcomes. Still, the low-FODMAP diet can provide effective short-term relief. One study found that low-FODMAP diets reduced symptom severity in 76 percent of patients with IBS compared to a 54 percent reduction in a group receiving standard diet advice. Bloating, flatulence, stool issues and abdominal pain were all reduced on the low-FODMAP diet. 


What foods have FODMAPs?

Now that we’ve established why low-FODMAP is an appropriate choice for symptom relief, let’s look at what foods contain FODMAPs:


  • Excess fructose: Apple, pears, mango, tinned fruit, watermelon, fruit juice, honey, HFCS, agave syrup, and dried fruit.
  • Fructans: Asparagus, artichoke, beets, garlic, leek, onion, shallots, cruciferous vegetables (broccoli, kale, cauliflower, cabbage, brussel sprouts, silver beet, bok choy), eggplant, fennel, celery, okra, chicory, dandelion leaves, wheat, corn, inulin, FOS, GOS, and rye.
  • Lactose: Milk, cream, cheese, butter, yoghurt, coconut milk/yoghurt/cream. Note that hard cheese is lower in lactose and may be tolerated compared to soft cheeses like cottage, brie, cream and ricotta.
  • Polyols: Xylitol, sorbitol, mushrooms, mannitol, maltitol, isomalt, STONE fruit (e.g. avocado and nectarines).
  • Galactans: Beans (including peanuts/peanut butter), lentils, peas and legumes (including soy products like tofu and soy milk).

*FODMAPs in foods can be decreased by various cooking and food preparation methods, therefore increasing people’s tolerance to raw vs cooked FODMAP foods. Also, lots of FODMAP foods are high in insoluble fiber that can be hard to digest in people with SIBO and inflamed guts, therefore cooking can help break down insoluble fiber and improve digestion/absorption of these foods. 


How does one go about implementing it sustainably without feeling overwhelmed and stressed?

If you have been diagnosed with IBS or SIBO and you have noticed that you react to some of the FODMAP foods listed above, we usually recommend removing all FODMAPs from your diet for a period of 30-60 days. This may seem like a lot, but in our clinical experience, most patients do not have the same reaction to each class of FODMAPs listed above. For example, some people seem to have no trouble with lactose but do very poorly with excess fructose. Others may tolerate polyols but not fructans. People can also react to foods in more than one class of FODMAPs (e.g. fructose and fructans).

Also, people react differently to each type of food in each class of FODMAPs. For example, someone may react to apples and pears in the fructose category, but tolerate all the other high fructose foods. 

Furthermore, reactions to FODMAP foods are usually dose dependent, meaning an over-consumption of a particular FODMAP food or group of FODMAP foods in a short space of time (e.g. one meal or one day) (especially if the foods are eaten raw) can lead to an exacerbation of symptoms. What is deemed as “over-consumption” is obviously different for every person and depends on their microbiome health (i.e. how inflammed their gut is).

Therefore, after the initial 30-day period – after symptoms have decreased, we then recommend reintroducing FODMAP foods back into the diet. We suggest adding FODMAP foods that a person regularly eats, one food at a time and one category at a time (e.g. re-add all the commonly eaten fructose foods back in, one at a time, then move to fructans). It is also important to eat the amounts that they usually eat on a day to day basis. The goal is to see what foods cause a reaction and in what amounts, as well as in what combinations. Ideally, the food reintroduction of a FODMAP food should occur only once in the day. If symptoms flare, wait until they subside in order to re-add the next food.

During the 30-60 day removal phase, lots of “gut healing” should be done by addressing diet and lifestyle factors that may be exacerbating SIBO symptoms, as well as using herbal/nutritional supplementation to decrease inflammation in the gut, improve digestion/absorption and improve the balance of gut flora. Normally the re-introduction phase occurs after this “gut healing” phase, which can sometimes improve people’s tolerance of certain FODMAP foods that they may have been once reacting to. . 

It’s rarely necessary to completely eradicate ALL FODMAPs from the diet because as mentioned above, most people don’t react to all of the FODMAPs, it is usually just a few of them. It is just a matter of figuring out which ones, in what amounts and in what combinations. If a person does not react to a particular FODMAP or only reacts at a certain threshold, then it is not necessary to remove it. 

Also, FODMAP intolerance is not like gluten or casein intolerance. In those cases, the immune system reacts —regardless of how much of that food you eat. With FODMAP intolerance, as explained above, it’s more of a threshold response.

If a person is eating a lot of FODMAPs daily, the threshold for tolerating FODMAPs will be quite low. However, if the overall intake of FODMAPs is low, the person may be able to tolerate small amounts without much problem. This can make things a little easier when people are eating out, traveling, or are in an environment where they don’t have as much control over their food choices.


The dangers of long-term low-FODMAP diets

The main reason to reintroduce as many FODMAP foods as possible that a person doesn’t react to, is due to their function as prebiotics. FODMAPs contain carbohydrates that are prebiotics in the gut, which help to feed the good bacteria in the large intestine, which are vital for our digestive health and overall health.

Long term FODMAP diets have been shown to starve the beneficial bacteria in the large intestine. These bacteria also help to fight against SIBO and IBS, and people with these conditions tend to have imbalances of bacteria in their large intestine as well. Therefore, by staying on long term, strict, low FODMAP diets, a person may be causing/exacerbating one problem, while trying to address another. 

Some people have found that even a few months on a low-FODMAP diet was sufficient to reduce their sensitivity to FODMAPs upon reintroduction. Other people have found that after being treated for SIBO/IBS via diet and lifestyle changes, as well as supplemental support, they have managed to re-introduce some FODMAPs in certain amounts that they once reacted to.

In saying that, some people may never be able to tolerate some particular types of FODMAPs despite treatment and removal/re-introduction. 



Digestive disorders are complex, multifactorial conditions. Therefore, along with a FODMAP diet, as mentioned above, other diet and lifestyle factors should be addressed, along with supplemental support to address the underlying drivers. A FODMAP diet is just a part of treatment for IBS and SIBO, it is not the only treatment. 

For more information regarding FODMAPs and digestive health, see this article here. 

If you suffer from digestive issues, especially IBS and SIBO, as well as food allergies and intolerancescall Oak Health today or book a consult online to find out how practical diet and lifestyle interventions, as well as herbal and nutritional supplementation can help improve your symptoms and overall well being. 
You may also be interested in the 6 week gut healing program.