IBS and low FODMAP diet

Irritable bowel syndrome (IBS) is known as a functional gastrointestinal disorder that is characterised by its predominant symptoms of abdominal pain, bloating, distention, constipation and diarrhoea. The onset of these symptoms can be very variable in nature and can have a debilitating impact on the daily lives of people.


What causes IBS is unclear. However, it is believed to be due to dysfunction between our brain and gut communicating. Its prevalence is higher than we think; about one in five of us have IBS.


Diagnosis of irritable bowel syndrome should only be made once any anatomical abnormalities, inflammatory bowel disease (IBD) and coeliac disease have been ruled out. Your GP may run a few blood tests to check faecal calprotectin levels for IBD, TTG to rule out coeliac disease and, if needed, may request endoscopy/colonoscopy. In some cases, you may also get referred to get further input from a gastroenterologist.

A word of caution - in the pursuit of getting answers for their symptoms, many people spend a fortune on food intolerance tests at this stage. But, in short, food intolerance tests are not validated. So, make an appointment with your GP to get a proper diagnosis.

Treatment for irritable bowel syndrome

For years, the dietary interventions to treat IBS have been unclear, however, in 2012, King’s College London published their first clinical trial on the low FODMAP diet. It revealed that a low FODMAP diet significantly improved the symptoms in about 50-80% of subjects.

Despite the improvement with a low FODMAP diet, it is recommended that before going on it, one must ensure that the following basic dietary changes are addressed:

  • eat slowly and do not rush through meals
  • eat smaller portions
  • reduce your intake of caffeine
  • if you are regularly drinking alcohol, think about reducing the intake
  • monitor your fat intake - if it is excessive, try and reduce it
  • avoid spicy food
  • if stress is exacerbating your symptoms, try mindfulness or yoga
  • avoid wearing tight clothes

What is the low FODMAP diet?

FODMAP stands for Fermentable Oligosaccharides Disaccharides Monosaccharides and Polyols. These are the short-chain fermentable carbohydrates.

Food is made of several components like proteins, fats and carbohydrates. Some of the short-chain carbohydrates i.e FODMAPs do not get absorbed well in the small intestine and travel through the large intestine, which is where billions of gut bacteria live. These bacteria will subsequently ferment the FODMAPs causing gas production and typical IBS symptoms. Fermentable carbohydrates also draw water into the large intestine causing loose stools.

My experience shows that about 80-90% of people do improve with a low FODMAP diet. Despite this, it is not a long-term diet. FODMAPs are good for your gut bacteria and being on this long-term can have a detrimental impact on your gut bacteria. This is why, after the exclusion phase, it is important to carry out a re-introduction.

How can a nutritionist help?

I have seen several patients in my clinic who, prior to seeing me, have sought Dr Google’s advice on this diet or have tried it using low FODMAP books/apps without much success. It is recommended to follow the low FODMAP diet under the guidance of a registered dietitian who is trained in delivering it, to guide you through both the exclusion and re-introduction phase appropriately.

The views expressed in this article are those of the author. All articles published on Nutritionist Resource are reviewed by our editorial team.

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Norwich, Norfolk, NR2 2HW
Written by Sejal Jacob, MSc RD Consultant Dietitian
Norwich, Norfolk, NR2 2HW

Sejal is a registered dietitian with an in-depth knowledge of adult and paediatric health and nutrition. She has over 10 years of experience within NHS and private practice working within various specialities to provide holistic support to her clients. Sejal is registered with the Health and Care Professional Council (HCPC) and is a member of BDA.

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