What Is the Low FODMAP Diet? A Beginner's Guide for IBS

Written by Robbie Clark, BExSc (Nutrition), M (Nutr+Diet), Accredited Practising Dietitian (APD) and Exercise Scientist · Last updated 16 October 2026 · 9 references

If your gut flares up after meals, you've probably come across the low FODMAP diet. It's one of the questions I'm asked about most as a dietitian. Here's what it is, how it works, how long to follow it and how to do it safely.

What are FODMAPs?

FODMAPs are a group of carbohydrates (sugars and fibres) found in many everyday foods, including wheat and other grains, legumes, some dairy foods, and many fruits and vegetables. FODMAP stands for:

• Fermentable
• Oligosaccharides – fructans (in wheat, rye, barley, onion and garlic) and galactans (in legumes)
• Disaccharides – lactose (in milk)
• Monosaccharides – excess fructose (in some fruits and honey)
• And
• Polyols – sugar alcohols such as sorbitol and mannitol, found in some fruits and vegetables and used as sweeteners

Why do FODMAPs cause IBS symptoms?

Everyone absorbs FODMAPs poorly. Instead of being absorbed in the small intestine, they travel to the large intestine, where gut bacteria ferment them and produce gas. They also draw water into the bowel.

For most people this goes unnoticed. People with IBS tend to have a more sensitive gut, so the same gas and fluid can cause pain, bloating, wind, nausea, and diarrhoea or constipation. How strongly you react depends on how much FODMAP you eat and how sensitive your gut is.

IBS is common. Depending on how it's defined, it affects roughly 4 to 9 in every 100 adults worldwide.¹

Does the low FODMAP diet work for IBS?

For many people, yes. When researchers compared the low FODMAP diet with other diets used for IBS, it ranked first for improving overall symptoms, abdominal pain and bloating.² Gastroenterology experts describe it as the diet with the most evidence behind it for IBS.³

It doesn't help everyone, though. If your symptoms haven't improved by the end of the first step, it's time to stop and try a different approach with your practitioner.³

The benefits can last. In a long-term study of people taught the diet by dietitians, more than half still had good symptom relief after reintroducing foods, and most were eating a nutritionally adequate diet.⁵

How does the low FODMAP diet work?

The diet has three steps. "Low FODMAP" doesn't mean "no FODMAP": the goal is to swap high-FODMAP foods for lower-FODMAP alternatives, not to cut out whole food groups.⁶

1. Low FODMAP (2–6 weeks). Swap high-FODMAP foods for lower-FODMAP alternatives and see whether your symptoms settle.
2. Reintroduction (usually around 2 months). Bring back one FODMAP group at a time, in increasing amounts, while the rest of your diet stays low FODMAP. This shows which groups trigger your symptoms and how much you can tolerate.
3. Personalisation (long term). Eat as widely as you comfortably can, limiting only the foods and amounts that cause you problems.

Don't skip the reintroduction step. Many FODMAP foods are rich in fibre and prebiotics that feed your gut bacteria, and restricting them for longer than you need makes it harder to eat a varied, nutritious diet.⁶

How long should you follow a low FODMAP diet?

Follow the strict first step for 2–6 weeks. Most people who respond notice a difference within that time. If you haven't improved by 6 weeks, the diet probably isn't the answer for you, so stop and talk to your practitioner.^3,6

Reintroduction takes another couple of months, and the personalised version can be kept up long term.^5,6

What should you do before starting a low FODMAP diet?

Gut symptoms can have many causes, so get IBS confirmed by your practitioner before changing your diet.^4,9 In particular:

• Get tested for coeliac disease first. The low FODMAP diet cuts back on wheat, rye and barley, and eating less gluten before testing can make the results unreliable.⁸
• See your practitioner promptly about warning signs, such as blood in your poo, unexplained weight loss, low iron (anaemia), symptoms that wake you at night, new symptoms after age 50, or a family history of bowel cancer, coeliac disease or inflammatory bowel disease.⁴
• You don't need a breath test. Hydrogen breath tests for fructose or lactose often give different results when repeated, so they're not a reliable guide to which foods to cut back.^4,7
• It isn't right for everyone. If you have a history of disordered eating, are pregnant or are already eating a very limited diet, talk to your practitioner before restricting foods.³

Which foods are high in FODMAPs?

Here are common examples for each FODMAP group. Serving size matters – some foods are fine in small amounts – and food data is updated regularly, so the Monash University FODMAP Diet app is the best place to check individual foods.⁶

Fructans and galactans

• Grains: wheat, rye and barley products such as bread, pasta, couscous, crackers and biscuits
• Vegetables: onion, garlic, leek, the white part of spring onion, artichoke, asparagus
• Legumes: chickpeas, lentils, baked beans and most dried or canned beans
• Nuts: cashews, pistachios

Lactose

• Cow, goat and sheep milk, yoghurt, ice cream, custard, and soft fresh cheeses such as ricotta and cottage cheese

Excess fructose

• Apples, pears, mango, honey, fruit juice concentrates and high-fructose corn syrup

Polyols

• Fruits: apples, pears, apricots, nectarines, plums, prunes, blackberries
• Vegetables: cauliflower, mushrooms
• Sweeteners: sorbitol (420), mannitol (421), xylitol (967), maltitol (965) and isomalt (953), often found in "sugar-free" gum and lollies

Examples of lower-FODMAP swaps

• Grains: rice, oats, quinoa, and wheat-free or sourdough spelt bread
• Vegetables: carrot, zucchini, capsicum, cucumber, potato, the green part of spring onion, and garlic-infused oil for flavour
• Dairy: lactose-free milk and yoghurt, and hard cheeses such as cheddar
• Fruit: oranges, kiwifruit, strawberries, grapes
• Protein: eggs, firm tofu, plain meat, chicken and fish

Frequently asked questions

Is the low FODMAP diet the same as a gluten-free diet?

No. Wheat, rye and barley are limited because they contain fructans, not because of gluten, and it's still unclear whether a gluten-free diet helps IBS.³

Can I do the low FODMAP diet without a dietitian?

You can, but working with a dietitian makes it more likely to work and helps you avoid cutting out more than you need to.³

How quickly will I notice a difference?

Most people who respond notice a difference within 2–6 weeks. If nothing has changed by 6 weeks, stop and talk to your practitioner.⁶

Do I need a breath test before starting?

No. Breath test results for fructose and lactose aren't reliable enough to guide your diet; reintroducing foods step by step is a better test.^4,7

Is the low FODMAP diet healthy long term?

The strict first step isn't meant to last, but the personalised diet you end up with can be nutritionally adequate and kept up long term.⁵

Does the low FODMAP diet cure IBS?

No. It doesn't cure IBS, but it can help you work out which foods trigger your symptoms and how much of them you can eat comfortably.⁶

References

Research (PubMed)

1. Oka P, Parr H, Barberio B, et al. Global prevalence of irritable bowel syndrome according to Rome III or IV criteria: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol. 2020;5(10):908–917. PubMed 32702295
2. Black CJ, Staudacher HM, Ford AC. Efficacy of a low FODMAP diet in irritable bowel syndrome: systematic review and network meta-analysis. Gut. 2022;71(6):1117–1126. PubMed 34376515
3. Chey WD, Hashash JG, Manning L, Chang L. AGA Clinical Practice Update on the role of diet in irritable bowel syndrome: expert review. Gastroenterology. 2022;162(6):1737–1745.e5. PubMed 35337654
4. Vasant DH, Paine PA, Black CJ, et al. British Society of Gastroenterology guidelines on the management of irritable bowel syndrome. Gut. 2021;70(7):1214–1240. PubMed 33903147
5. O'Keeffe M, Jansen C, Martin L, et al. Long-term impact of the low-FODMAP diet on gastrointestinal symptoms, dietary intake, patient acceptability, and healthcare utilization in irritable bowel syndrome. Neurogastroenterol Motil. 2018;30(1):e13154. PubMed 28707437

Australian guidelines

6. Monash University. The 3 steps of the FODMAP diet. View source
7. Monash University. How important is fructose breath testing in the FODMAP approach? View source
8. Coeliac Australia. Testing for coeliac disease. View source
9. healthdirect. Irritable bowel syndrome (IBS). View source

This article is general information, not medical advice. Speak with your practitioner about your own situation before changing your diet.