What is a Low-FODMAP Diet and How Can it Improve Symptoms of IBS?

FODMAP is an acronym for fermentable oligosaccharides, disaccharides, monosaccharides and polyols which are the types of carbohydrate that are fermented by the microorganisms that live in our intestines know as the ”microbiome”, resulting in increased gas production (methane), abdominal pain, bloating, diarrhea or constipation, or sometimes a combination of both.

The carbohydrate fermented by our gut organisms include simple sugars such as monosaccharides and disaccharides, as well as slightly longer molecules known as oligosaccaharides and a group of sugar alcohols known as polyols.

Monosaccharides are simple sugars such as glucose, fructose, galactose. Fructose is the sugar that makes fruit such as apples, pears and peaches sweet. Honey, prunes and dates, mango and papaya are also very high in fructose.

Disaccharides are two monosaccharide sugars joined together. Common table sugar is a disaccharide made up of a molecule of glucose and fructose.

An oligosaccharide is a short carbohydrate chain whose molecules are composed of a relatively small number of monosaccharide (such as glucose, fructose, galactose) units. Chains of fructose with one glucose molecule on the end are oligosaccharides known as fructans. Wheat is a major source of fructans in the diet, which means most breads, pasta, and pastry contain large amounts of fructans. Chains of galactose with one fructose molecule on the end are known as galactans. Foods rich in galactans are legumes (including soybeans, chickpeas, lentils), cabbage, and brussels sprouts.

Polyols are sugar alcohols that are found in sugar substitutes such as mannitol, xylitol, and sorbitol but they are also found naturally in fruit and vegetables such as cherries, avocado, plums, and mushrooms.

What is a low-FODMAP Diet?

A low FODMAP diet was first created in the early 2000s by Dr. Peter Gibson and Dr. Sue Shepherd to improve symptoms in Functional Gastrointestinal Disorders (FGIDs). Functional GI disorders are ones where there is no structural abnormality that can be seen when the person has tests including endoscopy, but they have frequent symptoms. These symptoms are thought to be related to gut—brain interaction, such as motility disturbance, visceral hypersensitivity, altered gut microbiota, and include a wide range of disorders or which Irritable Bowel Syndrome (IBS) is only one.

A low-FODMAP diet is frequently used to help reduce symptoms of Irritable Bowel Syndrome (IBS) and can be helpful for those who have been diagnosed with Inflammatory Bowel Disease (IBD) such as Crohn’s disease and Ulcerative Colitis when re-introducing foods after they have reduced symptoms following a Low Residue Diet.

Why do FODMAPs trigger symptoms?

FODMAPs are carbohydrates that are used by the gut microbiome as food. These bacteria, yeast and single-cell organisms live in the intestines help digest the food we eat and release by-products, as a result. Some of these by-products such as short-chain fatty acids can be helpful to the body, whereas other by-products may underlie unpleasant gastrointestinal (GI) symptoms.

When certain types of microbes ferment FODMAPs, one of the by-products they produce is methane gas which can contribute to feelings of bloating, abdominal pain, or cramping in individuals with IBS. Some types of FODMAPS also result in water being pulled into the intestines rather quickly, and which results in the diarrhea. Depending on the microbes and the FODMAPS they rely on, constipation can also be a symptom — whereas some people experience alternating periods of diarrhea and constipation.

What is the low FODMAP diet?

When used for those with functional GI disorders such as IBS, a low FODMAP diet is an elimination diet that involves removing high FODMAP foods from the diet for a period of 4 weeks or so and assessing whether the person feels better. If they do, it is assumed that some of the FODMAP foods are the ones underlying their symptoms problematic and we go about determining which ones they are not tolerating. After several weeks of the person not eating any foods with FODMAPS, we gradually reintroduce small amounts of foods that have lower amounts of FODMAPs and see how they feel. Foods that do not cause any symptoms are left in the diet, but those that result in symptoms are eliminated.

One Diet – in three stages

The Initial Stage of the Low-FODMAP Diet is where there is total elimination of FODMAP foods, and this stage lasts approximately 4 weeks. At the end of this stage, we evaluate to what degree symptoms have decreased. If symptoms have not decreased, I may recommend that we change approaches to evaluate other non-FODMAP factors that may be contributing to symptoms. If symptoms have decreased, then we carry on to the next stage of the Low-FODMAP Diet.

During the Intermediate Stage, specific foods with low levels of FODMAPs are gradually re-introduced over the following several weeks. How long a person remains at this stage varies with the person, the severity of their symptoms, and they level of comfort they have with reintroducing foods.

Finally, there is the Liberalization Stage of the Low-FODMAP Diet where the person gradually increases the amount of slightly higher FODMAP foods and begin to re-introduce new foods.

The Low-FODMAP Specialty Hour Service

I offer a one-hour specialty hourly service for those who want to take a low-FODMAP approach to reducing their unpleasant gastrointestinal symptoms.  I teach how to implement a low-FODMAP diet in 3 progressive stages, so that with my guidance people can find the level of FODMAP restriction that suits them best, without unnecessarily restricting foods that don’t cause them distress.

The first stage begins with a period of one-on-on instruction where I go over the detailed handout that I give them for following the elimination diet over the next 4 weeks. During that time, they can consult with me via email if they have questions, or if they want additional direction. At the end of the 4 weeks, we meet again and review their progress and make adjustments in what they are eating, if necessary. Then I go over the handouts for the next two stages and answer any questions they may have about implementing them sequentially.


People sometimes have ongoing problems with IBS — despite having learned a low-FODMAP diet elsewhere. They remain at a loss as to why they are still having symptoms. Sometimes it is because they did not implement the diet in distinct sequential stages — beginning with a period of complete elimination then gradually re-introducing foods from lower to higher FODMAP, and as a result never learned which foods are problematic, and which are not.

Oftentimes it is because they have not had any teaching about a specific category of food outside the standard low-FODMAP diet that even people without IBS do not tolerate well. These are foods which contain two specific oligosaccharides that should be cautiously re-introduced or avoided in people who know that they do not do well with some of those foods and which are beyond the scope of a standard low-FODMAP diet.

I teach these as part of the low-FODMAP service that I provide.

Gut Microbiome — environment and genetics

It was once thought that people are born with their unique types of gut bacteria, but recent twin studies have found that identical twins have very different types and amounts of gut bacteria — leading researchers to conclude that what we eat determines which gut bacteria multiply and which don’t. The extent to which different people produce methane gas in response to food seems to depend on the types of bacteria in one’s gut microbiome.

By avoiding the specific FODMAP foods that underlie symptoms we can greatly reduce the severity and frequency of symptoms that these gut bacteria produce as by-products.

More Info?

If your doctor has suggested that you could benefit from following a low-FODMAP diet, or you have previously learned a low-FODMAP somewhere but feel you missed some important aspects, please reach out to me and let know how I can help.

To your good health!


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5. Rothschild, D., Weissbrod, O., Barkan, E. et al. Environment dominates over host genetics in shaping human gut microbiota. Nature 555, 210—215 (2018). https://doi.org/10.1038/nature25973

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