IBS Diet: What to Eat First and How Low FODMAP Works

If your stomach bloats by the afternoon, you plan your day around where the toilets are, or you have started to feel nervous about eating out, you are probably looking for an IBS diet that helps. Food changes often do make a real difference. The trouble is that most advice online skips straight to the strictest version.

I'll take you through it in the order I would with a client. Diagnosis first, then the simple changes, and only then low FODMAP, done properly.

Do I need a diagnosis before changing my diet for IBS?

Yes. Please see your doctor before you start cutting foods out. Symptoms like bloating, pain and changes in bowel habit can come from other conditions too, and some of them, such as coeliac disease, need to be tested for while you are still eating normally. If you remove gluten first, the test can come back falsely reassuring.

Tell your doctor straight away if you notice blood in your stool, weight loss you cannot explain, symptoms that wake you at night, or a lasting change in your bowel habits. Those need checking, not a new diet.

What should I eat with IBS? Start here

Before anything restrictive, there are first-line changes that help a lot of people. They are not glamorous, and that is partly why they get skipped. Give them a fair try, a few weeks, before you decide they did not work.

• Eat regular meals. Three meals at roughly the same times each day, without long gaps. Your gut likes a routine.
• Do not skip meals and then eat a huge one. Big, late meals are a common trigger.
• Eat slowly and sit down to eat. Rushed eating means swallowing more air, which adds to the bloating.
• Notice fatty, fried and hot, spicy food. You may not need to cut them out, but smaller amounts are often easier to tolerate.
• Look at caffeine and alcohol. Both can irritate the gut in some people. Try cutting back for a couple of weeks and see what changes.
• Go easy on fizzy drinks and sugar-free sweets and gum, which can add to gas and loose stools.
• Adjust your fibre, rather than just adding more. If constipation is the main problem, increasing fibre slowly can help. If bloating is the problem, some types of fibre can make it worse.
• Drink enough water through the day, especially if you are increasing fibre.

Keep a simple food and symptom diary while you make these changes. Two weeks of honest notes tells us far more than guessing.

What is the low FODMAP diet?

FODMAPs are types of carbohydrate found in many everyday foods, including some fruits, vegetables, wheat, beans, lentils, milk, onion and garlic. In some people with IBS they draw water into the gut and are fermented by gut bacteria, which can cause bloating, wind, pain and changes in bowel habit.

The low FODMAP diet is not meant to be followed forever. It is a structured test with three phases.

The goal is the third phase: the widest, most normal diet that keeps your symptoms manageable. The first phase is only there to give you information.

Can I do the low FODMAP diet on my own?

You can, but this is where it most often goes wrong. A common pattern: someone downloads a food list, cuts out everything on it, feels better, and then stays there. Months later they are eating a small handful of "safe" foods, they are worried about every meal, and they have no idea which foods were the problem.

That matters for two reasons. Long-term restriction makes your diet less varied and can leave gaps in fibre, calcium and other nutrients. And many high FODMAP foods contain the kinds of fibre that feed helpful bacteria in your gut, so cutting them out for a long time is not ideal for your gut microbes either.

The other common problems are smaller but add up. Food lists online often disagree. Portion size matters, so a food can be fine in one amount and a trigger in another. And reintroduction is fiddly to do well on your own, so many people skip it, which means they never find out what they can eat again. If eating has started to feel tense and full of rules, it may be worth reading about building a healthier relationship with food alongside this.

Should I see a dietitian for IBS?

Low FODMAP is best done with a dietitian, and this is why: the value is in the reintroduction and personalisation, and that is where most people get stuck alone. My job is to check that the basics have been covered first, keep the restriction phase short and balanced, plan the reintroductions with you, and help you read your own results.

Because IBS support works best over a few weeks, with time between appointments to test things, I usually suggest my 3 sessions with a dietitian for this. We use the first session to look at your symptoms, your diary and the first-line changes, then plan the next steps together, with the following sessions spaced to fit the phases.

Is it worth paying for help with IBS?

This is a fair question, and the honest answer depends on where you are. If you have not tried the first-line changes above, start there. They cost nothing. If you have tried them, or you are already months into a restricted diet and feel stuck, guided support can save you months of guessing and money spent on special products. If you want to know what you would be paying for, I have written a straight breakdown of what an online dietitian costs.

Some people also feel they should be able to sort this out themselves, or worry about being judged for what they eat. You will not be. Most people I see with IBS have already tried hard on their own. Talking about bowel habits is a normal part of my working day, and if you are unsure what an appointment looks like, here is what to expect from a first session with a dietitian.

This article is general information about diet and IBS. It is not individual medical advice and does not replace a diagnosis or care from your doctor.