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What is IBS?

Written by Sophia Boothby

with contribution by Talia Cecchele

What is IBS?

Irritable Bowel Syndrome (IBS) is a common functional gastrointestinal (GI) or gut disorder characterised by changes in bowel habits (e.g. diarrhoea, constipation or both) and symptoms such as abdominal pain and bloating which are experienced at a level that impacts day to day life.

The term ‘functional disorder’ is a term used to describe a disorder (in this case in the GI tract) that occurs without any pathological (or physical) abnormalities, meaning that common medical investigations will often show normal results. IBS is a multifactorial functional disorder which includes the gut-brain axis communication link and it is now considered a disorder of the gut-brain interaction (1,2).

How is IBS diagnosed?

The Rome Foundation specifies the Rome IV criteria (3) for diagnosing and treating Disorders of Gut-Brain Interaction (DGBIs). According to IV criteria, the diagnostic criteria for IBS includes recurrent abdominal pain for at least 1 day a week for the past 3 months (symptoms to have started at least 6 months prior), associated with 2 or more of the below:

  1. Associated with bowel motion

  2. Associated with change in frequency of bowel motions

  3. Associated with a change in form or appearance of bowel motion (look down the loo to get to know your ‘normal’)

In the UK, we also have National Institute for Health and Care Excellence (NICE) guidelines that outlines the diagnostic tests that should be performed by your GP including blood tests and stool (or faecal) tests which check for inflammatory markers, antibodies related to coeliac disease, malabsorption and reviewing your risk of colorectal cancer (4).

IBS is categorised by subtypes according to symptoms experienced and using the Bristol Stool Chart which categorises our stools from Type 1 (hard pebble-like) to Type 7 (watery diarrhoea) (4).

  1. IBS- Constipation predominant (IBS-C) majority type 1 or 2 less than 3 times a week

  2. IBS- Diarrhoea predominant (IBS-D) - majority type 6 and 7 at least 3 times a day

  3. IBS- Mixed bowel habits (IBS-M) combination of constipation and diarrhoea stools

  4. IBS- Unclassified (IBS-U) - bowel motions are neither constipation, diarrhoea or mixed sub-types, however they meet other diagnostic criteria.

The Bristol Stool Chart (3)

Bristol Stool Chart (Lewis-and-Heaton-1997)

Is IBS the same as IBD?

IBS is separate from Inflammatory Bowel Disease (IBD) which can be diagnosed as Crohn’s Disease and Ulcerative Colitis (UC), however the symptoms individuals experience can be similar. IBD is a diagnosed disease which causes chronic inflammation to your GI tract. IBD can be seen in investigative imaging such as a colonoscopy. You should undergo the correct diagnostic tests for IBD as the treatment and management options are different to IBS, therefore it is important to seek medical advice.

Warning signs for IBS

If you are experiencing any of the symptoms described earlier at a level that are impacting on your quality of life, it is recommended that you discuss this with your GP. There are other key red flags that if experienced warrant seeking advice and investigations including unintentional weight loss, rectal bleeding (particularly if over 50 years old), family history of bowel or ovarian cancer, unknown cause of micronutrient deficiencies, over 60 years old with change in bowel habits of type 6 or 7 (5).

Treatment for IBS

Once diagnostic tests have been performed to rule out an organic cause (a cause that is medically observable or measurable) for your presenting symptoms, such as IBD, you may then be formally diagnosed with IBS by your Doctor. According to NICE guidelines the first line treatment begins with dietary and lifestyle advice and symptom-targeted medication.


Our diet is one of the key modifiable factors that shape our gut microbiota, which plays a crucial role in our gut health. First line dietary treatment is focused on general advice such as regular meals during the day and avoiding skipping meals or eating too late at night, and reviewing intake of; alcohol, caffeine, high fat/fried foods, dietary fibre diversity and fluids (6).

The key areas focused on will depend on the subtype of IBS and the primary symptoms of the individual. An important factor to remember is that dietary inclusion is vital to support our gut health and first line treatment should focus on adding to our diet to increase diversity, rather than eliminating foods or food groups.


British Dietetic Association summarises first line treatment including non-dietary approaches such as regular physical activity, mindfulness and stress-relief strategies. This includes gut directed hypnotherapy, and yoga that can be as effective as dietary modification (7). Yoga interventions includes different postures and breathing techniques aimed to relax both body and mind, targeting the gut-brain axis (8).

Low FODMAP diet & IBS

If there have been minimal improvements in functional gut symptoms following first line treatment advice, second line treatment might involve following an elimination diet under the guidance of a registered dietitian. This elimination diet is known as the low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) diet. FODMAPs are carbohydrates (types of sugars) which some people could form an intolerance to, which can lead to negative GI symptoms seen in IBS.

The low FODMAP diet includes three phases; an elimination phase, reintroduction phase and the personalisation phase. In practice, unfortunately many clients walk through our doors having followed the elimination diet for many months or even years. The low FODMAP diet is a 6-8 week diet that should only be followed for a short period for diagnostic purposes. We strongly advise against following the low FODMAP diet without the guidance from a trained registered dietitian.

Low FODMAP diet & disordered eating

Research indicates up to 98% of people with eating disorders experience IBS symptoms due to dietary restriction, malnutrition and engaging in compensatory behaviours such as purging, binge eating, and excessive exercise which can alter the gut microbiome and digestion (9). In eating disorders or recovery it is extremely common to experience the same symptoms which are experienced in IBS including abdominal bloating, pain, acid reflux and change in bowel habits such as constipation.

You can read more in our blog Digestive Issues in Eating Disorders.

It is a bit of a chicken or the egg scenario. Individuals living with IBS may link some foods with worsening of their symptoms resulting in following elimination diets, increased anxiety and fear around eating and development of disordered eating behaviours. And individuals without IBS who develop disordered eating, can go on to develop IBS as a side effect of their disordered eating and relationship with exercise and their body. Food elimination, such as following the low FODMAP diet can be used to mask disordered eating and eating disorders (10).

If you have disordered eating or are in recovery from an eating disorder, the low FODMAP diet is in most cases, not appropriate as it is too limiting and can worsen gut health and a person's relationship with food, often triggering further dietary restriction. A modified low FODMAP diet might be suitable further along in recovery, but usually weight restoration and restoring physical health is the priority as this alone can improve gut symptoms. It is important to work with a registered dietitian who can tailor advice based on your history and gut symptoms experienced.

At TCN our specialist eating disorder dietitians can offer online consultations to support your gut health journey! Book a free 15 minute discovery call here with one of our dietitians to see how we can support you.

Sophia Boothby

Guest Contributor

Sophia Boothy Specialist Community Dietitian

Sophia is a Specialist Community Dietitian within a London NHS Teaching Hospital specialising in gut health such as irritable bowel syndrome (IBS) and the low FODMAP diet, type 2 diabetes, PCOS, cardiac rehabilitation, and oral nutrition support. Sophia has recently developed her practice incorporating a non-diet and weight inclusive approach to nutrition with individuals presenting with disordered eating and restrictive eating behaviours, particularly alongside IBS. Find Sophia on Instagram at @eatforyoudietitian



  1. Chong, P.P., Chin, V.K., Loo,i C.Y., Wong, W.F., Madhavan, P. and Yong, V.C., 2019. The microbiome and irritable bowel syndrome–a review on the pathophysiology, current research and future therapy. Frontiers in microbiology, [online] 10 (1136), Available at: [Accessed 10 September 2022].

  2. Bercik, P, 2020..The brain-gut-microbiome axis and irritable bowel syndrome. Gastroenterology & Hepatology, [online] 16(6):322. Available at: [Accessed 10 September 2022].

  3. Rome Foundation. 2016. Rome IV Criteria - Rome Foundation. [online] Available at: <> [Accessed 20 September 2022].

  4. National Institute for Health and Care Excellence (NICE), 2008. Clinical guideline [CG61] Irritable bowel syndrome in adults: diagnosis and management. National Institute for Health and Care Excellence. Available at: Irritable bowel syndrome ( [Accessed 10 September 2022].

  5. Knott, L., 2021. Irritable Bowel Syndrome. Patient. Available at: -bowel-syndrome-pro [Accessed 4 October 2022].

  6. British Dietetic Association (BDA) UK Website. 2022. Irritable Bowel Syndrome Food Fact Sheet. [online] Available at: <> [Accessed 20 September 2022].

  7. McKenzie, Y.A., Bowyer, R.K., Leach, H., Gulia, P., Horobin, J., O'Sullivan, N.A., Pettitt, C., Reeves, L.B., Seamark, L., Williams, M. and Thompson, J., 2016. British Dietetic Association systematic review and evidence‐based practice guidelines for the dietary management of irritable bowel syndrome in adults (2016 update). Journal of Human Nutrition and Dietetics. [online] 29(5):549-75. Available at: [Accessed 10 September 2022].

  8. Schumann, D., Langhorst, J., Dobos, G. and Cramer, H., 2017. Randomised clinical trial: yoga vs a low-FODMAP diet in patients with irritable bowel syndrome. Alimentary Pharmacology and Therapeutics. [online] 47 (2): 203-211. Available at: [Accessed 4 October 2022].

  9. Perkins, S.J., Keville, S., Schmidt, U. and Chalder, T., 2005. Eating disorders and irritable bowel syndrome: is there a link?. Journal of psychosomatic research. [online] 1;59(2):57-64. Available at: [Accessed 27th September 2022]

  10. Sato, Y. and Fukudo, S., 2015. Gastrointestinal symptoms and disorders in patients with eating disorders. Clinical journal of gastroenterology. [online] 8(5):255-63. Available at: [Accessed 10 September 2022].


Talia Cecchele Nutrition is a team of registered dietitians that specialise in eating disorder recovery, disordered eating, digestive issues and sports nutrition. We aim to bring balance back to nutrition, help you to break free from food rules and find food freedom. We offer virtual consultations and group programs so whether you are based in London, the United Kingdom or around the world we would love to support you. To enquire about a private consultation please fill out a contact form.

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