Introduction
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 [3].
Breaking Down the FODMAP Carbohydrates
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 [1] 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 [2].
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 that 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, which results in 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.
The Three Stages of 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 problematic symptoms, and we go about determining which ones they are not tolerating.
Initial Stage: There is total elimination of FODMAP foods, lasting approximately 4 weeks. If symptoms have not decreased, I may recommend changing approaches to evaluate other non-FODMAP factors. If symptoms have decreased, then we carry on to the next stage.
Intermediate Stage: Specific foods with low levels of FODMAPs are gradually reintroduced over the following several weeks. Duration varies based on the person and symptom severity.
Liberalization Stage: The person gradually increases the amount of slightly higher FODMAP foods and begins to reintroduce new foods.
Beyond the Standard FODMAP Protocol
People sometimes have ongoing problems with IBS — despite having learned a low-FODMAP diet elsewhere. 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 that contain two specific oligosaccharides that should be cautiously reintroduced or avoided. I teach these as part of the low-FODMAP service that I provide.
The Gut Microbiome: Environment vs. Genetics
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 [4, 5]. 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?
Learn about me and how I can help you systematically implement a low FODMAP diet in three clinical stages to determine which FODMAP groups contribute to your symptoms. View my Low FODMAP Diet Package.
To your good health!
Joy
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References
- Gibson PR, Shepherd SJ. Evidence-based dietary management of functional gastrointestinal symptoms: The FODMAP approach. J Gastroenterol Hepatol. 2010 Feb;25(2):252-8. [https://pubmed.ncbi.nlm.nih.gov/20136989/]
- Drossman DA, Hasler WL. Rome IV-Functional GI Disorders: Disorders of Gut-Brain Interaction. Gastroenterology. 2016 May;150(6):1257-61. [https://pubmed.ncbi.nlm.nih.gov/27144617/]
- Jain V, Gupta K. Carbohydrate Analysis. In: Worsfold P, Townshend A, Poole C, editors. Encyclopedia of Analytical Science (Second Edition). Oxford: Elsevier Academic Press; 2005. p. 412-421. [https://www.sciencedirect.com/referencework/9780123693976/encyclopedia-of-analytical-science]
- Cahana I, Iraqi FA. Impact of host genetics on gut microbiome: Take-home lessons from human and mouse studies. Anim Models Exp Med. 2020 Sep 28;3(3):229-236. [https://onlinelibrary.wiley.com/doi/10.1002/ame2.12134]
- Rothschild D, Weissbrod O, Barkan E, et al. Environment dominates over host genetics in shaping human gut microbiota. Nature. 2018 Mar 8;555(7695):210-215. [https://pubmed.ncbi.nlm.nih.gov/29489753/]
© 2025 BetterByDesign Nutrition Ltd.
Joy is a Registered Dietitian Nutritionist and owner of BetterByDesign Nutrition Ltd. She has a postgraduate degree in Human Nutrition, is a published mental health nutrition researcher, and has been supporting clients’ needs since 2008. Joy is licensed in BC, Alberta, and Ontario, and her areas of expertise range from routine health, chronic disease management, and digestive health to therapeutic diets. Joy is passionate about helping people feel better and believes that Nutrition is BetterByDesign©.