Low FODMAP: the IBS diet that works, as long as you don't live on it.
It has the best evidence of any diet for irritable bowel syndrome. It is also a test, not a lifestyle. Here is how it works, what the studies found, and why you shouldn't do it alone.
The short version
- What it is
- A few weeks without certain fermentable carbs, then you test them back one group at a time.
- Good for
- Bloating, pain, wind and toilet chaos in diagnosed IBS.
- Bad at
- Being a forever diet. Also bad for your gut bacteria if you stay strict too long.
- Evidence
- Strong, for IBS. Nothing else.
- Our take
- A proper medical tool. Do it with a dietitian, finish all three steps, then eat as widely as your gut lets you.
What low FODMAP actually is
FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. Translation: a group of short-chain carbs and sugar alcohols that your small intestine absorbs badly. They sit in a lot of perfectly healthy food: onion, garlic, wheat, beans, apples, milk, cashews, mushrooms.
The low FODMAP diet is a three-step process built for people with irritable bowel syndrome (IBS), which affects around 4% of adults worldwide by the strict current definition.7 Step one: swap high-FODMAP foods for low-FODMAP ones for two to six weeks. Step two: test each FODMAP group back in, one at a time, and note what your gut does. Step three: eat everything you tolerate and keep limiting only what actually causes trouble.1
Most people only ever do step one. That's like reading the first chapter of a book and complaining it has no ending.
How it works in your body
FODMAPs that aren't absorbed in the small intestine do two things. They pull water into the gut, and they travel on to the large intestine, where your bacteria ferment them and make gas. Most people don't notice. In IBS, the gut seems to be more sensitive to stretching, so the same amount of gas and water hurts, bloats and sends you running.
Cut the FODMAP load and there's less to ferment. In a small Australian crossover trial, 30 people with IBS rated their overall symptoms roughly half as bad after three weeks of low FODMAP eating compared with a typical diet.2 The diet doesn't fix the sensitive gut. It just stops poking it.
What you eat, what you don't
These lists are for step one only. Portion size matters a lot: some foods are fine in a small serve and high in a big one. The Monash University FODMAP app has the tested amounts.1
Eat
- Meat, fish, eggs, firm tofu
- Rice, oats, quinoa, potatoes, rice noodles
- Carrots, zucchini, cucumber, spinach, bok choy, tomatoes, peppers
- Kiwi, oranges, strawberries, unripe banana
- Lactose-free milk and yoghurt, hard cheese
- Garlic-infused oil, chives, the green part of spring onions
- Water, black coffee, green tea
Forget it (for now)
- Onion and garlic, including in sauces, stock and spice mixes
- Wheat, rye and barley in large amounts: bread, pasta, Brezel
- Beans, lentils, chickpeas in normal portions
- Apples, pears, mango, watermelon, dried fruit
- Milk, soft cheese, ice cream
- Cashews, pistachios, mushrooms, cauliflower
- Sugar alcohols: sorbitol, mannitol, xylitol, maltitol (already on our never list)
Alcohol on low FODMAP
There are no proper trials on alcohol and IBS. In observational studies, about one in three people with IBS say alcohol sets off their symptoms.8 Alcohol can irritate the gut on its own, FODMAPs or not.
Tested low in FODMAPs
- One glass of dry white or red wine
- One beer
- Gin, vodka or whisky with soda water and lime
- A spritzer: wine topped up with soda water
Tested high, or a trap
- Rum
- Sweet dessert wine
- Red wine beyond about 250 ml
- Anything mixed with apple or mango juice, cola or sweetened mixers
The high list comes from Monash University's testing.8 Their tips: drink with food, alternate with water, and keep it small.
50 Club: not on a prescribed diet. Ask your doctor or dietitian what's safe for you. The general rules are in our alcohol guide.
What it's good for, with proof
IBS symptoms, and it beats the other diets
A 2022 network meta-analysis pooled 13 randomised trials with 944 people with IBS. Low FODMAP was the only diet that clearly beat people's usual eating for overall symptoms, and it ranked first for pain, bloating and bowel habit.3 The catch, in the authors' own words: most trials were in hospital clinics, and almost none tested the reintroduction step. We know step one helps. We know much less about the long game.
Feeling in control again
In a four-week London trial, 68% of people on the restricted diet reported adequate symptom relief, against 23% who kept eating as usual.4 Small study, 41 people, not blinded. Still, for a condition where people get told "it's just stress", that's a real result.
It's in the official guidelines
UK guidance from NICE says to consider a low FODMAP diet when general diet and lifestyle advice hasn't helped, and only with a healthcare professional who knows dietary management.5 Second-line, supervised. Not something to start because a podcast said so.
The uncomfortable truth
"FODMAPs are bad for you." No. Many of them are prebiotics: food for your good gut bacteria. When people with IBS cut fermentable carbs for four weeks, their bifidobacteria dropped clearly.4 Nobody knows yet what that means long term. That's exactly why step one is meant to last weeks, not years.
"I'm bloated, so I have IBS." Maybe. Or maybe coeliac disease, which is often misdiagnosed as IBS.6 Low FODMAP cuts down wheat (it isn't the same as gluten-free, but close), so it can hide coeliac symptoms and make the test unreliable. Get diagnosed first, then change your food.
The risks
- Missing something serious. Weight loss for no reason, bleeding from your bottom, bloody diarrhoea or a lump in your tummy need a doctor fast, not a food app.9
- Hiding coeliac disease. Cutting wheat before testing can give a false negative.6
- Getting stuck in step one. Staying strict for months shrinks your food list for no reason and may hurt your gut bacteria.4 Monash designed the diet to end in a wider, less restrictive way of eating.1
- Missing nutrients. Less wholegrain, fewer beans and less dairy can mean less fibre and calcium. A dietitian checks this. A blog doesn't.
- Food fear. A long list of "bad" foods can feed anxious or disordered eating. If you've had an eating disorder, talk to your doctor before any elimination diet.
- Local food is hard. Garlic and onion are in almost every hawker sauce and almost every Austrian Gulasch. Eating out takes planning, and that's tiring.
Allergies: watch the staples
Low FODMAP swaps often lean on foods that are major allergens. If you also have an allergy, both lists have to fit together.
| Low FODMAP staple | Allergen (EU list of 14)10 | Swap |
|---|---|---|
| Lactose-free milk and yoghurt, hard cheese | Milk | Rice drink with added calcium, firm tofu |
| Firm tofu, tempeh | Soy | Eggs, fish, chicken |
| Eggs | Eggs | Firm tofu, fish |
| Peanuts, peanut butter | Peanuts | Pumpkin and sunflower seeds |
| Walnuts, macadamias | Tree nuts | Pumpkin seeds, chia seeds |
| Spelt sourdough, oats | Cereals containing gluten | Rice, quinoa, potatoes |
| Prawns | Crustaceans | Fish, chicken |
| Gluten-free bread and crackers | Often eggs, soy, sesame or lupin | Read the label every time |
Don't do low FODMAP if you…
- haven't been diagnosed by a doctor yet
- haven't been tested for coeliac disease
- have weight loss, bleeding or other warning signs you haven't shown a doctor
- have ever had an eating disorder
- are under 18, pregnant or breastfeeding, unless a specialist dietitian runs it
- plan to do it without a dietitian
Healthen me asks about all of these and gives you a different plan if any apply.
How we use low FODMAP in your plan
We don't. Low FODMAP is a medical diet, and the elimination and the reintroduction belong with your doctor and a dietitian who knows IBS.
Healthen me asks about IBS and gut symptoms. If you say yes, we tell you to see your doctor and we don't set the FODMAP rules for you. What the plan can do: keep your meals simple, steer clear of our never list (which already bans the sugar alcohols), and leave out foods you tell us you react to. If your dietitian hands you a list of foods you tolerate after step three, you can remove the rest as dislikes. Our fasting and Rebel Day rules don't replace anything your dietitian says.
This article is general information, not medical advice. If you have a medical condition or take medication, talk to your doctor before changing how you eat.
Sources
- Monash University. Starting the low FODMAP diet. Monash FODMAP, IBS Central. monashfodmap.com/ibs-central/i-have-ibs/starting-the-low-fodmap-diet
- Halmos EP, Power VA, Shepherd SJ, Gibson PR, Muir JG. A diet low in FODMAPs reduces symptoms of irritable bowel syndrome. Gastroenterology 2014;146(1):67–75.e5. doi.org/10.1053/j.gastro.2013.09.046
- 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. doi.org/10.1136/gutjnl-2021-325214
- Staudacher HM, Lomer MCE, Anderson JL et al. Fermentable carbohydrate restriction reduces luminal bifidobacteria and gastrointestinal symptoms in patients with irritable bowel syndrome. Journal of Nutrition 2012;142(8):1510–1518. doi.org/10.3945/jn.112.159285
- Hookway C, Buckner S, Crosland P, Longson D. Irritable bowel syndrome in adults in primary care: summary of updated NICE guidance. BMJ 2015;350:h701. doi.org/10.1136/bmj.h701
- NHS. Coeliac disease. nhs.uk/conditions/coeliac-disease; and Coeliac disease: diagnosis. nhs.uk/conditions/coeliac-disease/diagnosis
- Sperber AD et al. Worldwide prevalence and burden of functional gastrointestinal disorders, results of Rome Foundation Global Study. Gastroenterology 2021;160(1):99–114.e3. doi.org/10.1053/j.gastro.2020.04.014
- Clarke E (Monash University). Going dry for July? How alcohol can impact IBS. Monash FODMAP blog, 2022. monashfodmap.com/blog/going-dry-july-how-alcohol-can-impact-ibs
- NHS. Symptoms of IBS (irritable bowel syndrome). nhs.uk/conditions/irritable-bowel-syndrome-ibs/symptoms
- Regulation (EU) No 1169/2011 on food information to consumers, Annex II (the 14 allergens). eur-lex.europa.eu/eli/reg/2011/1169/oj