If you live with IBS, you probably know the routine. You plan your day around toilets, your stomach swells by mid-afternoon, and you’ve cut out half your favourite foods without really knowing which ones are the problem.
You may also have heard of the low FODMAP diet for IBS. It’s the best-researched dietary approach we have for irritable bowel syndrome. It is also one of the most misunderstood. Many people find a list online, cut everything out, feel a bit better, and then get stuck. They’re afraid to eat anything new, and they never quite know what their gut can actually handle.
In this post I’ll explain what FODMAPs are, how the diet works, who it helps (and who it doesn’t), and why doing it with proper guidance makes such a difference.
What are FODMAPs?
FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols. Put simply, they’re a group of short-chain carbohydrates that some people don’t absorb well in the small intestine.
There are five main types:
Fructans: wheat, rye, onion, garlic, leeks
Galacto-oligosaccharides (GOS): beans, lentils, chickpeas
Lactose: milk, yoghurt, soft cheeses
Excess fructose: apples, pears, mango, honey
Polyols: sorbitol and mannitol, found in stone fruits, mushrooms, cauliflower and sugar-free gum
FODMAPs are not “bad” foods. Most of them are healthy, and many feed your beneficial gut bacteria. The issue is how a sensitive gut responds to them.
How does the low FODMAP diet work for IBS?
When FODMAPs aren’t absorbed, two things happen. They draw water into the small intestine, and when they reach the large intestine, your gut bacteria ferment them and produce gas.
In most people this goes unnoticed. In people with IBS, the gut is often more sensitive to stretching (this is called visceral hypersensitivity). The same amount of gas and fluid that someone else wouldn’t feel can cause pain, bloating, urgency, diarrhoea or constipation.
Lowering FODMAPs reduces that water and gas, so there’s less stretching and fewer symptoms. In a well-known controlled trial from Monash University, people with IBS had their overall gut symptoms roughly halved on a low FODMAP diet compared with a typical diet.
If bloating is your main complaint, you may also find my post on why you might always feel bloated helpful. Not all bloating is FODMAP-related.
The three phases (this is where most people go wrong)
The low FODMAP diet is not a long-term elimination diet. It’s a short learning process in three phases.
1. Restriction (2 to 6 weeks)
You swap high FODMAP foods for low FODMAP alternatives. The goal is to see whether your symptoms settle. If nothing has changed after four to six weeks, FODMAPs probably aren’t your main driver, and there’s no point continuing.
2. Reintroduction (around 6 to 8 weeks)
You test one FODMAP group at a time, in gradually increasing amounts, while keeping everything else low. This shows you which groups you react to and how much you can tolerate. This is the phase people most often skip or get lost in. It’s also the most valuable part.
3. Personalisation (long term)
You bring back everything you tolerate, and keep only your real triggers in check, often in smaller portions rather than cutting them out completely. The aim is the widest, most varied diet possible with good symptom control.
Does the low FODMAP diet work?
The research is genuinely encouraging:
Across at least 10 randomised trials, around 50 to 80% of people with IBS respond, with the biggest improvements in bloating, wind, pain and diarrhoea.
A 2022 network meta-analysis of 13 trials found the low FODMAP diet ranked first of all dietary approaches for overall IBS symptoms.
The British Society of Gastroenterology recommends it as a second-line dietary therapy, when basic diet and lifestyle changes haven’t been enough.
It’s also worth being honest: it doesn’t work for everyone. Around a quarter to a half of people don’t respond. If you’re in that group, other things are likely at play: stress and the gut-brain axis, constipation, sleep, gut motility or something else that needs looking into.
The downsides of doing it alone
The restriction phase is meant to be short for good reasons.
Your gut bacteria notice. Many FODMAPs are prebiotics. A trial from King’s College London found that four weeks of restriction reduced Bifidobacteria, one of the beneficial bacteria groups. The reassuring news is that when people moved on to reintroduction and personalisation, symptom relief lasted and Bifidobacteria levels were back in line with baseline after 12 months.
Nutrition can slip. Cutting wheat, dairy, legumes and many fruits and vegetables at once can leave gaps in fibre, calcium and other nutrients if the replacements aren’t planned well.
Food fear creeps in. Staying in the restriction phase for months is common. It makes eating out, travel and social meals stressful, and it can make the gut more sensitive over time, not less. If you have a history of disordered eating, a restrictive diet like this may not be right for you, and that’s an important conversation to have first.
Why it works best with support
This isn’t just me saying it. Research and clinical guidelines both point to the low FODMAP diet working best when it’s guided by a trained professional.
In a small trial comparing ways of learning the diet, 80% of people who had one-to-one sessions reported adequate symptom relief, compared with 39% of those who were given leaflets. Even more telling, almost two thirds of the one-to-one group felt confident they could actually follow the diet. In the leaflet group, only 6% did.
That matches what I see in practice. The theory looks simple on paper. The tricky parts are the real-life details: hidden onion and garlic in stock cubes and sauces, portion sizes that change a food from low to high FODMAP, testing foods in a way that gives you a clear answer, and knowing when a reaction is FODMAPs and when it’s a stressful week.
Mario's tip
Onion and garlic are the two ingredients my clients miss most. The FODMAPs in them (fructans) don't dissolve in oil, so you can still get the flavour. Gently heat a few garlic cloves or onion pieces in olive oil, then remove them before cooking. You keep the taste and leave the FODMAPs behind. The green parts of spring onions and chives are also low FODMAP and add a lovely oniony note.
Simple low FODMAP swaps to get you started
You don’t need to overhaul your kitchen. A few easy swaps:
Wheat bread or pasta → sourdough spelt, rice, oats, potatoes, gluten-free pasta
Milk and soft cheese → lactose-free milk, hard cheeses like manchego or parmesan
Apples, pears, mango → oranges, strawberries, pineapple, green kiwi
Onion and garlic → garlic-infused oil, chives, spring onion greens
Beans and lentils → firm tofu, eggs, or small portions of canned and rinsed lentils
Green kiwi deserves a special mention. It’s low FODMAP and has good evidence for constipation, which makes it a great choice if you have IBS-C. I’ve written more about it in my post on kiwi benefits for constipation.
IBS rarely travels alone
Many people with IBS also deal with reflux, fatigue, low mood, or anxiety around food. Their gut is often part of a bigger picture that includes stress, sleep, hormones and daily routine. If reflux is part of your story, have a look at my post on acid reflux and GERD. The triggers can overlap, but they’re not the same.
This is why I don’t see the low FODMAP diet as the whole answer. It’s a very useful tool. It works best as part of a wider plan that looks at why your gut has become so sensitive in the first place.
Before you start: see your doctor
Please don’t start a low FODMAP diet before IBS has been diagnosed by a doctor. Symptoms like yours can also come from coeliac disease, inflammatory bowel disease or other conditions that need medical care. Coeliac testing in particular needs to happen before you cut out wheat, or the test may not be accurate.
How I can help
If you’ve tried to go low FODMAP on your own and found it confusing, or you’ve been stuck in the restriction phase for too long, you’re not alone. This is exactly the work I do with clients.
Together, we will:
Look at the full picture first: your symptoms, history, routine, stress and current diet, so we know whether low FODMAP is the right tool for you
Make the restriction phase easy and nourishing, with practical meal ideas that fit your life, not just a list of “no” foods
Guide you step by step through reintroduction, so you get clear answers about your own triggers
Build a long-term way of eating that’s as varied and relaxed as possible
Work on the root causes, such as gut-brain stress, bowel habits and sleep, so you’re not relying on restriction forever
I work with clients online in English and German, and in person in Barcelona.
Ready to stop guessing and start understanding your gut? Book a consultation and let’s work through this together.
FAQ
What is the low FODMAP diet for IBS?
The low FODMAP diet is a short-term, three-phase approach for IBS. You first reduce fermentable carbohydrates (FODMAPs) for 2 to 6 weeks, then reintroduce them one group at a time to find your personal triggers, and finally build a varied long-term diet that only limits the foods you truly react to.
Does the low FODMAP diet work?
For many people, yes. Randomised trials show that around 50 to 80% of people with IBS improve, especially with bloating, wind, pain and diarrhoea. A 2022 network meta-analysis ranked it first among dietary approaches for IBS. It doesn't work for everyone, and if symptoms haven't improved after 4 to 6 weeks, it's worth looking at other causes.
How long should I follow the low FODMAP diet?
The strict restriction phase should only last 2 to 6 weeks. After that you move on to reintroduction, which usually takes 6 to 8 weeks. Staying on full restriction for months can affect your gut bacteria and nutrient intake and make eating stressful, so it isn't recommended.
Is the low FODMAP diet bad for gut bacteria?
Short-term restriction can reduce beneficial bacteria such as Bifidobacteria, because many FODMAPs act as prebiotics. Research suggests that moving on to reintroduction and personalisation helps bring them back towards normal levels, which is one reason the later phases are so important.
Do I need a nutritionist to do the low FODMAP diet?
You can try it on your own, but research and clinical guidelines recommend support from a trained professional. In one trial, people who had one-to-one guidance were twice as likely to report adequate symptom relief as those given leaflets. Support is especially helpful during reintroduction, which is where most people get stuck.
When should I see a doctor about IBS symptoms?
Always see your GP before starting the diet so other conditions such as coeliac disease or inflammatory bowel disease can be ruled out. See a doctor promptly if you notice blood in your stool, unexplained weight loss, night-time symptoms, persistent vomiting, a family history of bowel cancer or a significant change in bowel habits, especially after age 50.
View scientific references
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