Irritable bowel syndrome diet: what to eat and what you need not cut out

What is irritable bowel syndrome and how is it diagnosed?

Irritable bowel syndrome, or IBS, is pain or discomfort in the abdomen linked to bowel habit. It appears or changes when you go to the toilet, and comes with diarrhoea, with constipation or with both alternating. You may also see it called mucous colitis or spastic colon, which are the same thing.

Doctors diagnose it using the Rome V criteria, published in 2026. These require abdominal pain or discomfort on at least three days a month over the last three months, and it must not be constant [3]. It must also be related to at least two of these three things: defecation, a change in the frequency of bowel movements, or a change in their form [3].

The British gastroenterology guideline classifies it as a disorder of gut-brain interaction [1]. It is not an illness of the mind or a character problem. It is a gut that hurts in response to stimuli that would not hurt someone else, and that reacts to stress because the two systems are closely connected.

The diagnosis is made by your GP or your gastroenterologist, after ruling out other causes of the same symptoms.

Can irritable bowel syndrome be cured?

There is no treatment that makes it disappear for good, and it is wise to be wary of anyone promising a definitive solution. It can usually be managed. There are long good periods, and flare-ups get shorter when you know what triggers them.

Knowing this early takes away a lot of fear. Irritable bowel syndrome does not damage the intestine or turn into something else. It is very uncomfortable but breaks nothing. If you also have bloating almost every day, the guide to bloating and abdominal distension covers that symptom in detail.

What can I eat if I have irritable bowel syndrome?

More than you think. The first thing the British guidelines recommend is eating at regular times, without skipping meals, without rushing and without large meals [2]. They also advise spreading fibre across several meals instead of concentrating it [2]. This is the starting point, before removing any food.

Next comes the type of fibre, which is where most confusion arises. Insoluble fibre, such as wheat bran, speeds up transit and tends to increase gas and pain, which is why it is advised against in irritable bowel syndrome [2]. Soluble fibre forms a gel that thickens diarrhoea and softens constipation. It is found in oats, ground linseed, boiled carrot, quince paste and apple.

If your pattern leans towards constipation, the constipation diet covers that part. Psyllium, a soluble fibre, can ease the symptoms of irritable bowel syndrome [1]. If you need it, it is prescribed by your doctor or your dietitian-nutritionist. It is not the starting point, and it is not something to begin on your own.

Milk is similar. If lactose disagrees with you, lactose-free milk and yoghurt are available. If you prefer a plant-based drink, the one made from soya protein is low in FODMAPs, while the one made from whole soya beans is not [4]. Choose one with at least 3% protein, and bear in mind that soya is an allergen.

Are eggs bad for irritable bowel syndrome?

No. Eggs contain no FODMAPs, the fermentable carbohydrates that cause the most trouble in irritable bowel syndrome. In the Monash University classification, which maintains the FODMAP food table, eggs are among the foods you can eat [4].

It is one of the questions we are asked most often in consultations, and in a general plan eggs stay. If you notice that they disagree with you in particular, take them out for two or three weeks and then bring them back, with someone to structure the test.

Do oranges and citrus fruits inflame the gut?

No. Orange and mandarin are low in FODMAPs in a normal portion [4], and they are not among the foods removed in a low-FODMAP diet. Lemon, in the amount in which it is used, a squeeze or a slice, is not either.

With fruit, amount and timing matter more. Spread through the day, it is usually better tolerated than all at once, and whole fruit is better than juice.

Apple is the case people ask about most, and it deserves the full nuance. It is rich in pectin, the fibre that helps, but it is also among the fruits highest in FODMAPs [4]. During the elimination phase it is removed. Afterwards it is reintroduced, and cooked it is usually better tolerated than raw.

Do I need to cut out gluten?

First, coeliac disease needs to be ruled out. The British guidelines recommend a coeliac disease test for anyone with irritable bowel syndrome symptoms [2]. That test is only valid if you take it while eating gluten. If you remove gluten beforehand, it can come back negative even if you are coeliac, and you are left without a diagnosis.

Wheat allergy is a different matter, and your doctor investigates it separately. If either is confirmed, gluten or wheat comes out of the diet.

If everything comes back negative, some people still improve without wheat. Most likely, gluten has nothing to do with it. Wheat, barley and rye are among the foods highest in fructans, one of the FODMAP groups, which is why removing them sometimes eases symptoms. For the same reason, not everything labelled “gluten-free” agrees with you. Onion contains no gluten and is one of the foods that causes the most bloating.

What is the low-FODMAP diet and how long does it last?

FODMAP is an English acronym for a group of short-chain carbohydrates. They are fermentable oligosaccharides, disaccharides and monosaccharides, and polyols. The small intestine absorbs them poorly, and some, such as the fructans in wheat or onion, nobody absorbs. They reach the large intestine, draw in water and are fermented by bacteria. In irritable bowel syndrome the gut reacts more strongly to that gas and distension, which explains the bloating and pain.

The low-FODMAP diet was developed by Monash University and has three phases [5].

• Elimination, for two to six weeks [5]. No longer.
• Reintroduction. Groups are reintroduced one at a time, in order and with a record, to see which one causes trouble and how much you tolerate.
• Personalisation. You keep the broadest diet that suits you, which is almost never the one from the first phase.

It is used as a second-line option, after the general measures, and it is supported by a trained dietitian-nutritionist [1] [5].

If the same sugar always appears during reintroduction, there may be a fructose intolerance or a sorbitol intolerance behind it. These are confirmed with a hydrogen breath test; commercial intolerance tests are not suitable for this.

How long does it take to notice, and how do you “reduce inflammation in” the gut?

With the general measures there is no fixed timeframe. Some people notice changes early and others need more time. If nothing has changed after a few weeks, it is time to review the next step with a professional.

The elimination phase does have a time limit, two to six weeks [5]. If nothing has changed after six weeks, that diet is not the way forward, and you go back to eating as before while another approach is sought.

One clarification about the word. Irritable bowel syndrome is not an inflammatory disease [1], so no food or herbal infusion “reduces its inflammation”. What feels bloated is gas moving poorly and an abdominal wall that gives way outwards. It is managed with regular meal times, fibre and patience, not with remedies.

What mistakes do we see in consultations?

Some mistakes come up almost every week.

• Removing ten foods at once. If you improve, you do not know which one it was, and if you do not improve, you no longer know what to reintroduce.
• Starting the low-FODMAP diet on your own and staying in the elimination phase for months, with no end date.
• Blaming the last food eaten for a bad day. Stress and sleep also move the gut, and without a record you can attribute a bad spell to a food for no reason.
• Searching for lists of “foods that inflame the colon”. They only make the list of removals longer.