Dear Dietitian

22 April, 2026

Marianne Williams is a dietitian specialising in allergies, IBS, and increasingly, people living with stomas, all of whom may benefit from a low FODMAP diet. Marianne came to our attention thanks to one of her patients, Olivia Madden.

Living with IBS symptoms from my teens has given me first-hand insight into how disruptive gut problems can be. My experience led me to a degree in Human Nutrition and Dietetics, specialising in gut health. I first learned about the low FODMAP diet at a King’s College London lecture in 2009 and went on to complete their first UK FODMAP training course for dietitians in 2010. I then established the first gastroenterology dietetic-led NHS service in 2012. Since then, I have supported thousands of people with IBS-type gut symptoms, including people living with a stoma.

What are ‘FODMAPs’?

FODMAP is an acronym from ‘fermentable oligosaccharides, disaccharides, monosaccharides, and polyols’.

FODMAPs are present in certain fruits, vegetables, legumes, some nuts, cereals, lactose, and polyols (often used as artificial sweeteners). Some of these foods can increase the amount of water entering the small intestine, leading to loose and/or urgent stools, while others are indigestible and ferment in the gut causing wind, bloating and pain.

Why FODMAPs matter with a stoma

Most of the research on the low FODMAP diet has been done on people with IBS and other functional bowel disorders, rather than specifically in stoma populations. However, it is generally accepted that ostomates who experience high-output, bloating, abdominal pain, or diarrhoea may also benefit from a low FODMAP diet, as FODMAPs can increase luminal water and gas production, exacerbating these symptoms.

Many ostomates find that a carefully supervised low FODMAP approach can reduce wind and diarrhoea-type output.

Examples of high FODMAP foods that can trigger symptoms

The exact details should always be tailored to you, but common examples include:

• Vegetables such as onions, garlic, leeks, cauliflower, mushrooms and sprouts
• Fruits such as apples, pears, mango, cherries and any stone fruits
• Pulses like chickpeas, lentils and kidney beans
• Wheat-based products such as regular bread, pasta, or biscuits
• Dairy products high in lactose, like regular milk, some yoghurts and ice-cream
• Sugar alcohols (polyols) found in ‘sugar-free’ gums, mints, sweets and some diabetic or diet products
• Honey, agave syrup and treacle

Lower FODMAP options are often better tolerated

• Fruits such as green-tipped bananas, oranges, berries, and kiwi
• Vegetables such as carrots, courgettes, spinach, peppers, parsnips, and the green tops of spring onions (chives also work well)
• Grains such as rice, oats, quinoa, and smaller portions of suitable gluten-free breads or pastas. 100% spelt sourdough bread is also well tolerated
• Lactose-free dairy products or hard cheeses
• Simple sugars in modest amounts, such as table sugar or maple syrup

Portion size is also crucial

Food may be low FODMAP in a small amount but high in a larger serving. This is one reason professional guidance is so important, particularly when you also have to consider your specific stoma output and challenges.

Why specialised dietary advice is important

The low FODMAP diet is a specialist, medical nutrition therapy. Leading gastroenterology guidelines recommend it is only used under the supervision of a dietitian/nutritional expert with specific FODMAP training. It should:

• Be time-limited in its strict phase
• Be carefully adapted for stoma type, output, and your general health
• Always include a clear reintroduction and personalisation plan

Starting a strict low FODMAP diet from the internet or from handouts, without up-to-date, specialist advice, can worsen nutritional status, increase anxiety around food, and delay proper diagnosis of other conditions.

If you are considering this approach and have a stoma, the safest route is to see a specialist gastroenterology/FODMAP dietitian who can tailor the plan to your medical history and lifestyle (see further details at the end of this article).

How the FODMAP diet usually works in practice:

Step 1: Your dietitian will usually start by reducing or eliminating the intake of fermentable foods for 4 to 8 weeks, allowing the gut symptoms to reduce.

Step 2: Foods are then reintroduced one by one to find out which of the FODMAP foods were particularly problematic and may need to be restricted in the future, and which of the foods can be eaten freely with no risk of symptoms.

Step 3: Finally comes the personalisation of the diet. Each patient will react differently to different foods. Each patient will create a uniquely modified FODMAP-containing diet based on tolerance to foods identified in step 2. Most people are back to relatively normal eating after 6 months, but with the knowledge of what foods trigger their symptoms.

How quickly you might see change

When the plan is followed correctly and is appropriate for the individual, many people notice:

• Less bloating and wind
• Reduced cramps or abdominal pain
• More predictable, less watery stoma output

Patients often see these results within 1 – 3 weeks, though some need a bit longer. If there is no real improvement after 4 – 6 weeks of a well-implemented plan, it may suggest that FODMAPs are not the main driver of your symptoms, and other causes should be explored with your medical and dietetic team.

Other important considerations for stoma patients

People with a stoma already have extra nutritional considerations. When layering a low FODMAP diet on top, ostomates must also consider:

• Nutrient deficiencies

Long-term, poorly supervised FODMAP restriction can reduce intake of fibre, calcium, iron, zinc, folate, B vitamins and vitamin D. This matters even more for stoma patients, who may already have higher losses or altered absorption.

• Gut bacteria (microbiota)

Many high FODMAP foods are also important ‘prebiotics’ that feed beneficial gut bacteria. A prolonged very low FODMAP diet can reduce the diversity of these bacteria. Reintroduction and personalisation are therefore essential, and in some cases a suitable probiotic may be recommended.

• Age and other health conditions

Older adults and those with additional conditions (such as inflammatory bowel disease, coeliac disease, diabetes, or kidney problems) need especially careful, individualised advice to keep the diet safe and balanced.

In summary…

If the FODMAP diet is successful then it can change people’s lives, making them able to travel, socialise and work without the constant worry of suffering with embarrassing or distressing symptoms.

Where to get more support

• Specialist low FODMAP and IBS webinars created by gastroenterology dietitians:
  www.patientwebinars.co.uk
  www.wisediet.co.uk

These resources are there to inform and empower you, but they are not a substitute for one-to-one assessment. If you recognise yourself in this article, the next step is to book in with a specialist FODMAP dietitian to explore whether this approach is right for you.