IBS and Gut Symptoms: What You Should Know Before Changing Your Diet

By Dr Timothy Eden, MBBS, RD from Eden Health and Nutrition

Read time approx. 4mins

As a GP and registered dietitian working in the UK, I wanted to write this post because almost every week in clinic I meet patients who have lived with bowel or stomach symptoms for months – sometimes years – before seeking help. Many have tried to self-manage using magazine articles, online blogs, or word of mouth. While that shows initiative, it often leads to frustration and limited success. I also hear the “low FODMAP diet” mentioned almost daily, but this is a highly restrictive approach that is not meant to be a first-line strategy and can be harmful if done without the right support. This post aims to give a clear, evidence-based overview of what to expect if you see your GP, and some first steps you can try safely with diet.

How stomach symptoms present and how common IBS is

Bowel and stomach complaints are among the most common reasons people visit their GP. Symptoms include bloating, abdominal pain, cramping, diarrhoea, constipation, or fluctuating bowel habits. Irritable Bowel Syndrome (IBS) is one of the most frequent diagnoses, with prevalence estimates around 10–15% of adults in the UK (BDA, 2023). Although IBS is not life-threatening, it can have a major impact on quality of life.

Types of IBS and the Rome criteria

IBS is diagnosed clinically, using the Rome IV criteria (Drossman, 2016). These state that IBS is:

Recurrent abdominal pain, on average, at least one day per week in the last three months, associated with two or more of the following:

• related to defecation,

• associated with a change in stool frequency,

• associated with a change in stool form.

  Subtypes are based on stool pattern:

• IBS-C: constipation-predominant

• IBS-D: diarrhoea-predominant

• IBS-M: mixed type (alternating diarrhoea and constipation)

• IBS-U: unsubtyped

3. Who is most commonly affected?

IBS affects more women than men, with onset usually between ages 20–40 (BSG, 2021). Symptoms often persist long-term, though severity may fluctuate. Stress, dietary triggers, and illness can exacerbate episodes.

4. What your GP may do before diagnosing IBS

Although IBS is a diagnosis of exclusion, GPs will usually perform some baseline tests to rule out other conditions. According to NICE CG61: Irritable bowel syndrome in adults (NICE, 2017, updated), this may include:

• Full blood count, CRP or ESR (to exclude inflammation/anaemia).

• Coeliac serology (IgA tissue transglutaminase and total IgA).

• Faecal calprotectin (particularly in those <40 years with diarrhoea) to exclude inflammatory bowel disease.

Your GP will also screen for “red flag” features such as unexplained weight loss, rectal bleeding, change in bowel habit in people >50, or family history of bowel/bowel cancer. If present, urgent referral will be made in line with NICE NG12: Suspected cancer: recognition and referral.

5. First-line dietary advice before restrictive diets

Both the British Dietetic Association (BDA) and the British Society of Gastroenterology (BSG) recommend that initial management should focus on simple dietary and lifestyle changes, rather than jumping straight to elimination diets (BDA Food Fact Sheet, 2023; BSG Clinical Guidelines, 2021).

These include:

• Trial of probiotics: A 4–6 week trial of a reputable probiotic can be considered. Certain strains (e.g. Bifidobacterium infantis 35624 for bloating/abdominal pain; Saccharomyces boulardii for diarrhoea) may be more effective depending on symptoms. The BSG advises at least a 6-week trial before judging effect.

• Reduce ultra-processed foods (UPF): Diets high in processed, fatty, and sweetened foods are linked to worse gut symptoms. NICE also highlights dietary triggers such as caffeine, alcohol, and fizzy drinks as worth limiting (NICE CG61).

• Gradually increase fibre intake: Soluble fibre can improve symptoms in IBS-C and IBS-M. Good examples include oats, bananas, apples, carrots, courgettes, and psyllium husk (ispaghula). Insoluble fibre (e.g. bran, seeds, skins) can worsen bloating in some patients and should be introduced cautiously.

• Trial short-term reduction of common culprits: Instead of a full FODMAP elimination, patients may benefit from short-term avoidance of high-fermentable foods such as onions, garlic, beans, and brassicas. Keeping a food and symptom diary can help identify personalised triggers.

6. Getting further support

If symptoms don’t improve, referral to a dietitian may be appropriate. In the NHS, this often involves structured dietitian-led webinars or group sessions before one-to-one input, in line with local pathways. NICE and BDA both emphasise that the low FODMAP diet should only be offered under dietitian supervision, given its complexity and risk of nutritional inadequacy.

7. Key take-home

IBS is common and can be very distressing, but safe and effective strategies exist. Starting with simple, evidence-based changes often helps, while ensuring other conditions are ruled out. Don’t suffer in silence, and don’t feel pressured into extreme diets without professional support. Your GP and dietitian can guide you step by step.

References

• NICE (2017, updated). Irritable bowel syndrome in adults: diagnosis and management (CG61).

• NICE (2015). Suspected cancer: recognition and referral (NG12).

• BDA (2023). Food Fact Sheet: Irritable Bowel Syndrome (IBS). British Dietetic Association.

• BSG (2021). British Society of Gastroenterology guidelines on the management of irritable bowel syndrome.

• Drossman DA et al. (2016). Rome IV diagnostic criteria for functional gastrointestinal disorders. Gastroenterology.