Nutrition and Irritable Bowel Syndrome: Finding a Balanced, Individual Approach

What is irritable bowel syndrome?

Irritable bowel syndrome, commonly known as IBS, is a disorder of gut-brain interaction. It can cause abdominal pain, bloating, excessive wind and changes in bowel habits without the structural inflammation or damage seen in conditions such as inflammatory bowel disease.

Symptoms may include constipation, diarrhoea or a mixture of both. They can fluctuate over time and may be influenced by food, stress, sleep, hormones, illness, medication and changes in routine.

IBS is commonly grouped according to the predominant bowel pattern:

• IBS-C: constipation is the predominant symptom.
• IBS-D: diarrhoea is the predominant symptom.
• IBS-M: both constipation and diarrhoea occur.
• IBS-U: symptoms do not fit clearly into the other groups.

IBS should be properly assessed

Symptoms that resemble IBS may occasionally be caused by another condition. Assessment may include discussion of symptoms, medical and family history, medications, dietary intake and appropriate pathology.

Depending on the symptoms, a doctor may recommend testing for conditions such as coeliac disease, inflammatory bowel disease, infection, anaemia or thyroid dysfunction.

Start with the foundations

Many people begin by removing foods they believe may be causing symptoms. Before undertaking a restrictive diet, it is often helpful to establish regular eating patterns and address factors that can disturb digestion.

Helpful first steps may include:

• Eating regular meals and avoiding long gaps without food.
• Eating slowly and chewing food thoroughly.
• Choosing portions that are satisfying without causing excessive fullness.
• Drinking adequate fluid, particularly when constipation is present.
• Reviewing large amounts of caffeine, alcohol and carbonated drinks.
• Reducing very large, rich or high-fat meals when these aggravate symptoms.
• Increasing fibre gradually rather than suddenly.
• Maintaining regular movement and physical activity.
• Supporting sleep and managing stress where possible.

These strategies will not resolve every case of IBS, but they provide a useful foundation and make it easier to identify which additional dietary changes are genuinely helpful.

Fibre is not all the same

Fibre can affect stool consistency, bowel transit, gut bacteria and fermentation. The type of fibre is important because different fibres can have very different effects on IBS symptoms.

Soluble fibres absorb water and may form a soft gel within the bowel. They can help soften hard stools while also adding consistency to loose stools. Psyllium, also known as ispaghula husk, has some of the strongest evidence for improving overall IBS symptoms.

Foods and products that may provide soluble fibre include:

• Oats.
• Psyllium or ispaghula husk.
• Chia seeds.
• Linseeds or flaxseeds.
• Kiwi fruit.
• Some fruits and vegetables.
• Legumes, when tolerated.

Coarse insoluble fibre, such as large amounts of wheat bran, can worsen pain, urgency or bloating for some people with IBS. This does not mean that all wholegrain foods need to be avoided.

Fibre supplements should generally be introduced at a low dose and increased gradually. A rapid increase can cause additional gas, bloating or abdominal discomfort. Adequate fluid is also important, particularly when using psyllium.

What are FODMAPs?

FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. These are short-chain carbohydrates that may be incompletely absorbed in the small intestine.

FODMAPs can draw water into the bowel and are fermented by gut bacteria. In people with a sensitive digestive system, the resulting changes in fluid and gas can contribute to pain, bloating, distension, diarrhoea or altered bowel habits.

FODMAPs occur naturally in many nutritious foods, including some fruits, vegetables, legumes, grains and dairy products. A food being high in FODMAPs does not mean that it is unhealthy or that everyone with IBS needs to avoid it.

The low-FODMAP diet is not intended to be permanent

A low-FODMAP diet can improve symptoms for some people with IBS, but it should be approached as a structured process rather than a lifelong list of prohibited foods.

The process has three stages:

1. Short-term restriction. High-FODMAP foods are temporarily reduced and replaced with nutritionally appropriate alternatives. This phase is commonly limited to approximately two to six weeks.
2. Reintroduction. Individual FODMAP groups are systematically challenged to determine which types and amounts cause symptoms.
3. Personalisation. Foods that are tolerated are returned to the diet, while only genuine triggers are limited in amounts that are necessary for symptom control.

When symptoms do not improve during the initial phase, continuing a highly restrictive low-FODMAP diet is unlikely to be helpful. Other causes and treatment strategies should be considered.

The long-term goal is the least restrictive diet that provides acceptable symptom control. Reintroducing tolerated foods supports dietary variety, nutritional adequacy, social eating and exposure to fibres that may benefit the gut microbiome.

Do gluten and dairy need to be avoided?

Not everyone with IBS needs to avoid gluten or dairy products.

Some people who react to wheat may be responding to wheat fructans, which are FODMAP carbohydrates, rather than gluten itself. Coeliac disease should also be considered before commencing a strict gluten-free diet because removing gluten can make coeliac testing less reliable.

Lactose can cause symptoms when it is not adequately digested. However, lactose tolerance varies, and many people can tolerate smaller portions, hard cheeses, yoghurt or lactose-free milk. Unnecessary removal of dairy may reduce calcium, iodine, protein and vitamin intake unless appropriate replacements are included.

Nutrition for constipation-predominant IBS

For IBS with constipation, management may include:

• Gradually increasing soluble fibre.
• Using psyllium when appropriate.
• Maintaining adequate fluid intake.
• Eating regular meals to stimulate normal bowel activity.
• Including regular movement and physical activity.
• Allowing time for a consistent toileting routine.
• Reviewing medications or supplements that may contribute to constipation.

Simply adding large amounts of bran or fibre without sufficient fluid can increase discomfort and may not improve constipation.

Nutrition for diarrhoea-predominant IBS

For IBS with diarrhoea, it may be helpful to review:

• Large amounts of caffeine.
• Alcohol.
• Very fatty meals.
• Excess fruit juice.
• Sugar-free products containing sorbitol, mannitol or other polyols.
• Lactose, when lactose intolerance is suspected.
• Individual FODMAP triggers.
• Whether another condition or medication may be contributing.

Excessive dietary restriction is not the solution. The aim is to identify specific triggers while maintaining enough food, fluid, protein, fibre, vitamins and minerals.

The gut-brain relationship

The digestive system and nervous system communicate continuously. Stress, anxiety, poor sleep and previous difficult experiences can increase gut sensitivity or alter bowel function.

This does not mean that IBS is imaginary or that symptoms are all in the mind. The pain and bowel symptoms are real. It means that treatment can involve both gastrointestinal and nervous-system strategies.

Depending on the individual, useful treatments may include gut-directed psychological therapy, cognitive behavioural therapy, hypnotherapy, relaxation strategies, regular exercise and improved sleep routines alongside nutrition and medical care.

What about probiotics?

Probiotics may help some people, but research results vary between products and bacterial strains. A benefit from one probiotic cannot automatically be assumed for another.

When trialling a probiotic, use one product at a time, follow the recommended dose and monitor symptoms. Stop the product if symptoms worsen or there is no meaningful improvement after a reasonable trial.

Avoid becoming trapped in an increasingly restricted diet

IBS symptoms can create understandable anxiety around eating. However, repeatedly removing foods without structured reintroduction can lead to nutritional deficiencies, reduced food enjoyment, social isolation and increased fear of symptoms.

Signs that further dietetic support may be needed include:

• A very limited list of foods considered safe.
• Fear of eating outside the home.
• Unintentional weight loss.
• Difficulty meeting energy or protein needs.
• Multiple suspected food intolerances.
• Persistent symptoms despite extensive food avoidance.
• A history of an eating disorder or disordered eating.

Why seeing a dietitian can be important

IBS symptoms and food triggers vary considerably between individuals. Advice that helps one person may be ineffective or unnecessarily restrictive for another. A dietitian can help determine whether dietary changes are likely to be useful while protecting nutritional adequacy, food variety and quality of life.

Professional guidance is particularly important before commencing a restrictive diet such as the low-FODMAP diet. Without appropriate reintroduction, people may continue avoiding many nutritious foods that they can actually tolerate. This can reduce fibre, calcium, iron, protein, vitamin and overall energy intake and may negatively affect the gut microbiome.

A dietitian can help:

• Review symptoms, bowel patterns, usual food intake and possible dietary triggers.
• Identify whether irregular meals, inadequate fibre, low fluid intake or excessive restriction may be contributing to symptoms.
• Recommend appropriate soluble fibre strategies for constipation, diarrhoea or mixed bowel symptoms.
• Decide whether a structured low-FODMAP trial is appropriate.
• Guide the reintroduction of FODMAP groups to identify individual tolerances.
• Prevent unnecessary long-term avoidance of gluten, dairy, legumes, fruit, vegetables or wholegrains.
• Ensure that dietary changes continue to provide adequate energy, protein, fibre, calcium, iron and other essential nutrients.
• Adapt recommendations for vegetarian, vegan, culturally diverse and family eating patterns.
• Recognise symptoms or nutritional concerns that require further medical investigation.
• Support people who have food anxiety, disordered eating or a history of an eating disorder.

The best IBS diet is not the diet that removes the greatest number of foods. It is the least restrictive eating pattern that provides acceptable symptom control while supporting nutritional health, social eating and a confident relationship with food.

References

1. Lacy BE, Pimentel M, Brenner DM, et al. ACG clinical guideline: management of irritable bowel syndrome. American Journal of Gastroenterology. 2021;116(1):17–44. DOI: 10.14309/ajg.0000000000001036.
2. 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.
3. 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.
4. Monash University. The three-step FODMAP diet. Accessed June 2026.