What Are FODMAPs? How the Low FODMAP Diet Works
Updated October 2026
FODMAPs are carbohydrates that the small intestine absorbs poorly. In many people with irritable bowel syndrome (IBS), they trigger bloating, abdominal pain, diarrhoea or constipation. On the FODMAP diet, you cut them out as far as possible for a few weeks and then test which ones you tolerate. This guide explains what the six FODMAP groups are, how the three phases work and what the research says.
Key points
- FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. These are short-chain carbohydrates that the small intestine absorbs poorly.
- In the gut, they draw in water and are fermented by bacteria. A sensitive gut responds with pain and bloating.
- The diet has three phases: elimination for 2 to 6 weeks, reintroduction for 8 to 12 weeks and then a personalised diet for the long term.
- According to Monash University, symptoms improve in about three out of four people with IBS. The diet cannot cure IBS.
What are FODMAPs?
FODMAP is an acronym for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols. These are short-chain carbohydrates and sugar alcohols that the small intestine absorbs only partly or not at all. ‘Fermentable’ means that gut bacteria break them down.
The concept comes from researchers at Monash University in Melbourne. They used it to develop the low FODMAP diet, often simply called the FODMAP diet. To this day, the team measures the FODMAP content of foods in its own laboratory.
Good to know: FODMAPs are not unhealthy. Fructans and GOS are types of fibre and feed beneficial gut bacteria. Most people eat high FODMAP foods every day without any problems. That is why the diet is only meant for people who react to them with symptoms.
Why FODMAPs cause symptoms
What happens to FODMAPs in the gut is the same for everyone. The difference lies in how sensitive the gut is.
In the small intestine, they draw in water. Because FODMAPs are poorly absorbed, they stay in the gut and hold on to fluid there.
In the large intestine, they are fermented. Gut bacteria break them down and produce gas in the process. Fructans and GOS always get this far, because humans cannot digest them.
The gut wall stretches. The water and gas increase the volume inside the gut. Most people hardly notice this.
A sensitive gut reacts strongly. In IBS, the nerves in the gut signal even normal stretching as pain. Other symptoms include bloating, a feeling of fullness, and diarrhoea, constipation or alternating bouts of both.
So FODMAPs do not cause IBS, but they are a common trigger for symptoms. Stress, very fatty food, coffee, alcohol or large meals can also irritate the gut.
The six FODMAP groups
Monash University divides FODMAPs into six groups. Each is found in different foods, and not everyone reacts to all of them. The diet helps you find out which groups give you trouble.
Sources include wheat, rye, barley, onions, garlic and inulin.
Sources include beans, lentils, chickpeas, cashews and pistachios.
Sources include milk, yoghurt, quark and ice cream.
Sources include honey, agave syrup, apples, pears, mango and asparagus.
Sources include apricots, plums, avocado and sugar-free chewing gum.
Sources include mushrooms, celery and sauerkraut.
Other sugar alcohols such as xylitol (birch sugar), maltitol and isomalt are also polyols. They are mainly found in sugar-free sweets.
Often the amount is what counts. Many foods are low FODMAP in small portions and only become a problem in larger ones. Our FODMAP list of more than 350 foods shows how individual foods compare. For exact amounts in grams, see the Monash FODMAP app.
The FODMAP diet in three phases
The FODMAP diet does not mean cutting foods out for good. It is a test in three steps, and it ends with a diet that restricts you as little as possible.
1Elimination
2 to 6 weeks
You replace high FODMAP foods with low FODMAP ones until your symptoms have clearly settled.
2Reintroduction
8 to 12 weeks
You test the FODMAP groups one at a time with increasing amounts and note how you react.
3Personalisation
long term
You eat everything you tolerate again and only limit what causes symptoms.
Timings based on the current information sheet from Monash University (2026). How long it takes you depends on how quickly your symptoms settle.
Phase 1: Elimination. Low FODMAP does not mean FODMAP-free. You choose foods and portions that are low in FODMAPs and otherwise eat as varied a diet as possible. If your symptoms have clearly improved after two to six weeks, move on to phase 2. If nothing has changed after six weeks, staying on the diet for longer will do little good. In that case, something else may be behind your symptoms, or a different treatment may work better.
Phase 2: Reintroduction. This is the most important part of the diet. You test one FODMAP group after another and stay low FODMAP in between. That way you find out what you react to, and at what amount. You will find the process, test foods and starting amounts in our reintroduction test plan.
Phase 3: Personalisation. Everything you tolerate well becomes a regular part of your diet again. You limit groups that cause symptoms only as much as you need to. Your tolerance can change over time, so it is worth testing again after a few months.
How well does the FODMAP diet work?
A low FODMAP diet is one of the best-studied dietary treatments for IBS. Studies by Monash University show that symptoms improve in about three out of four people with IBS. A 2022 analysis of 13 randomised trials with 944 participants concluded that it came out best of the diets compared.
The evidence has its limits, though. Most studies lasted only a few weeks and took place in specialist clinics. A diet is also hard to blind, because participants can tell what they are eating. The British Society of Gastroenterology (BSG) rates the quality of the evidence as very low, but still recommends the diet when general dietary advice is not enough.
The German S3 guideline on IBS (DGVS and DGNM, 2021) lists a low FODMAP diet as a treatment option.
NICE and the BSG recommend it as the next step after general dietary advice.
The diet is intended for people with diagnosed IBS.
The diet does not cure IBS, but it can help you get your symptoms under control. About one in four people see no improvement. If that applies to you, there are other options, including soluble fibre such as psyllium husk, exercise, gut-directed hypnotherapy, cognitive behavioural therapy or medication.
Who is the FODMAP diet for?
The diet was developed for adults with IBS. For other symptoms, it is not automatically a good idea. To find out how IBS is diagnosed and which other treatments are available, read our article Irritable bowel syndrome: symptoms, causes, diagnosis and treatment.
Suitable if
- IBS has been diagnosed and other causes have been ruled out
- general advice such as eating regular meals and cutting down on coffee, alcohol and fatty food has not helped enough
- you are prepared to pay close attention to what you eat for a few weeks and then test carefully
- your inflammatory bowel disease is in remission but IBS-like symptoms persist
Not suitable, or only with caution
- for weight loss, which the diet is not designed for
- if you have or have had an eating disorder, or if you are underweight
- for children, as the diet was developed for adults
- if your symptoms are new, very severe or unexplained
Blood in your stool, unintentional weight loss, fever, diarrhoea at night or anaemia do not fit IBS and can have another cause. Symptoms that only start after the age of 50 and a family history of bowel cancer, coeliac disease or inflammatory bowel disease also count as warning signs.
Symptoms similar to IBS can also be caused by coeliac disease, endometriosis or inflammatory bowel disease. Coeliac disease is diagnosed with a blood test (tTG-IgA and total IgA) and, in adults, usually also with tissue samples from the small intestine. Both are only reliable while you are eating wheat, rye and barley as usual. On the FODMAP diet you eat much less of them, so a test may then give a false negative result.
Getting started with phase 1
A little preparation makes the elimination phase easier and your results more reliable.
Keep a diary for a week. Before you start, note down what you eat and how you feel. That way you can see later what has changed. You can do this on paper or in the Monash FODMAP app.
Read labels. Onion and garlic powder, inulin, honey, fructose syrup and sugar alcohols turn up in many ready-made products, from stock to cereal bars.
Watch your portions. Many foods are only low FODMAP up to a certain amount. Several small portions in one meal can add up, as our article on FODMAP stacking explains.
Simple everyday swaps
| Instead of | Try |
|---|---|
| Onions and garlic | Garlic-infused oil, chives, the green parts of leeks and spring onions, onion and garlic replacers |
| Wheat bread and wheat pasta | Spelt sourdough bread, gluten-free bread without inulin, rice or corn pasta |
| Milk, yoghurt and ice cream | Lactose-free products, hard cheese such as Parmesan or Gruyère |
| Apples, pears and mango | Oranges, kiwi, blueberries, strawberries and fresh pineapple |
| Honey and agave syrup | Maple syrup or sugar in normal amounts |
| Beans and chickpeas | Firm tofu, small portions of canned lentils or chickpeas |
For more foods with traffic light ratings, see our FODMAP list. If you want to make your own stock, our article on low FODMAP stock shows you how.
Many people find it hardest to do without onions and garlic. These products are low FODMAP and bring back the flavour:
Fody Garlic-Infused Olive Oilgarlic flavour without fructans
FreeFOD Garlic Replacer1 tsp replaces one clove
FreeFOD Onion Replacer1 tsp replaces one onion
Massel Vegetable Stock Powderno onion or garlic
Common mistakes and how to avoid them
The elimination phase is designed to last 2 to 6 weeks. Studies show that the number of bifidobacteria in the gut can fall after just four weeks. What this means in the long term is still unclear.
Without testing, you do not know what you tolerate and may be restricting your diet for no reason. Many people only react to certain groups.
Dropping whole food groups can easily leave you short of fibre, and going without dairy can leave you short of calcium. So swap foods rather than just leaving them out.
Apple and pear juice, camomile and fennel tea, strongly brewed chai and rum are high in FODMAPs. Water, black coffee, peppermint tea and green tea, on the other hand, are low FODMAP.
Enzymes such as FODZYME change the FODMAP content of a meal, which skews your test results. Once testing is over, they can be useful in everyday life. Read more in our article on reintroduction.
Stress, lack of sleep and too little exercise can also irritate the gut. Note these factors in your diary as well. That makes your test results easier to interpret.
Frequently asked questions about the FODMAP diet
What does FODMAP stand for?
FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. These are short-chain carbohydrates such as fructans, lactose and fructose, and sugar alcohols such as sorbitol. The small intestine absorbs them poorly, and in the large intestine they are fermented by bacteria.
How long does the FODMAP diet last?
The strict phase lasts 2 to 6 weeks, and reintroduction usually takes 8 to 12 weeks. So it takes around three to four months to find the diet that suits you. After that, you go back to eating as normally as possible.
How soon will I know if the diet is working?
Some people notice a difference within a few days, while for others it takes a few weeks. That is why the elimination phase is designed to last 2 to 6 weeks. If nothing has improved after six weeks, it is better not to extend the diet.
Is the FODMAP diet gluten-free?
No. With wheat, rye and barley, it is usually the fructans that cause problems in IBS, not the gluten. Gluten-free products are therefore not automatically low FODMAP, and small amounts of wheat, such as in soy sauce, are usually fine. Read more in our article FODMAP vs gluten.
Do I have to avoid FODMAPs for good?
No. After reintroduction, you eat everything you tolerate again. Many people only react to certain groups, or only to larger amounts. Avoiding FODMAPs completely would not be good for your gut bacteria either.
Do enzymes like FODZYME help?
According to the manufacturer, FODZYME breaks down fructans, GOS and lactose while they are still in the food. It does not work on free fructose or polyols. During reintroduction, it is best not to use it, so that your test results remain meaningful. Read more in our FODZYME FAQ.
Is the FODMAP diet useful if I do not have IBS?
No. There is no evidence of any benefit for people without digestive symptoms, and the diet is not meant for weight loss. In fact, high FODMAP foods such as pulses, wholegrains, fruit and vegetables are especially good for most people.
Sources: Monash University, About FODMAPs and IBS · Monash University, The 3-step FODMAP Diet (2026) · DGVS and DGNM, German S3 guideline on irritable bowel syndrome (2021) · NICE, Irritable bowel syndrome in adults (CG61) · Vasant et al., BSG guidelines on the management of IBS (Gut 2021) · Black et al., Efficacy of a low FODMAP diet in IBS (Gut 2022) · Staudacher et al., Fermentable carbohydrate restriction reduces luminal bifidobacteria (J Nutr 2012)
