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Irritable bowel syndrome: the diet has the strongest evidence

Two diets and one fibre beat most supplements, and peppermint oil is the herb with the best data.

remedy

IBS is a disorder of gut-brain interaction: the gut is structurally normal and behaves abnormally, with pain, bloating and a changed bowel habit. Three interventions have the best evidence, and none of them is exotic.

The low-FODMAP diet. FODMAPs are fermentable oligo-, di-, monosaccharides and polyols — short-chain carbohydrates that draw water and ferment in the colon. A low-FODMAP diet has randomised trial evidence for symptom improvement in IBS, and the effect size is larger than most supplements produce. The important caveat is the procedure: it is a three-phase protocol (strict elimination 4-6 weeks, then structured reintroduction to identify personal triggers, then long-term personalisation) and it should be done with a dietitian. A permanently restricted low-FODMAP diet narrows the diet, changes the microbiome, and is not the treatment.

Soluble fibre — psyllium specifically. Psyllium improves symptoms in IBS, whereas insoluble bran often worsens them. This distinction matters: "eat more fibre" is wrong advice for IBS in general, and psyllium is the fibre with the trials.

Peppermint oil. Covered on its own page; the pooled finding is superiority over placebo with low certainty and more adverse events (mostly reflux). Enteric-coated capsules.

Probiotics. Pooled analyses find a modest benefit, with the honest caveats that strains differ, preparations are unstandardised, and the trials are heterogeneous. A reasonable trial for 4 weeks, then decide on the person's own record.

What the person can do without any of this. A written symptom-and-food diary over 4-6 weeks, eating regular meals, reducing caffeine and alcohol, and treating the stress axis seriously — gut-directed hypnotherapy and cognitive behavioural therapy both have randomised evidence in IBS, which is unusual and worth knowing about, and neither is a "just relax" dismissal.

The red flags are the reason IBS is a diagnosis of exclusion. IBS should not be diagnosed in someone with bleeding, weight loss, anaemia, or new symptoms over 50 without the alternatives being excluded.

What the studies found

Preparation

Psyllium

• 1 teaspoon (about 5 g) in a large glass of water, once daily, increasing to twice if tolerated
• Drink plenty of water; start small
• Separate from other medicines by 2 hours

Peppermint oil

• Enteric-coated capsules, about 180-200 mg, two to three times daily before meals
• Swallow whole. Chewed or burst capsules cause heartburn.

Caraway, fennel and anise

• Crushed seed, 1-2 g per 250 mL, covered, 5-10 minutes, after meals
• Traditional antispasmodic aromatics; evidence is thin but they are harmless and pleasant

Low-FODMAP elimination — the shape of it

• 4-6 weeks strict, then reintroduce one FODMAP group at a time over several weeks, keeping the diary
• Do this with a dietitian. Without the reintroduction phase it becomes a permanent, unnecessary restriction.
• High-FODMAP foods most often implicated: onion, garlic, wheat, apples, pears, stone fruit, legumes, lactose, sorbitol and mannitol sweeteners

A probiotic trial

• Pick one product with a named strain and take it for 4 weeks
• Keep a simple symptom score; stop if nothing has changed by four weeks rather than buying a second one

The gut-brain interventions

• Gut-directed hypnotherapy and CBT: both have randomised evidence in IBS. A clinician or a psychologist can refer.

Cautions and interactions

• Do not stay on strict low-FODMAP long term. It is an elimination protocol, not a diet.
• Insoluble bran often worsens IBS. Psyllium is the fibre with the evidence.
• Peppermint oil worsens reflux. See the reflux page.
• Probiotics are risky in the critically ill or immunocompromised.

When this is not a self-care problem — get help

• Blood in the stool, unintentional weight loss, anaemia, a new change in bowel habit over 50, nocturnal diarrhoea that wakes you, or a family history of bowel cancer or coeliac disease — investigate, do not accept an IBS label.
• Coeliac disease should be excluded in anyone with IBS-type symptoms before a lifetime of dietary restriction. Do not start a gluten-free diet before testing — it invalidates the test.

Related

• Peppermint oil and peppermint tea for IBS and indigestion
• The gut microbiome: what is actually established
• Constipation: fibre, water, and when a laxative is the wrong tool
• Acute diarrhoea: rehydration first, everything else second
• Inflammatory bowel disease: curcumin, boswellia and the rule about supplements

Sources

1. Efficacy of dietary interventions in irritable bowel syndrome: a systematic review and network meta-analysis. The lancet. Gastroenterology & hepatology 2025; doi:10.1016/S2468-1253(25)00054-8 PubMed 40258374
2. Efficacy of interventions for the treatment of irritable bowel syndrome, functional abdominal pain-not otherwise specified, and abdominal migraine in children: a systematic review and network meta-analysis. The Lancet. Child & adolescent health 2025; doi:10.1016/S2352-4642(25)00058-6 PubMed 40246358
3. The Efficacy of Probiotics, Prebiotics, Synbiotics, and Fecal Microbiota Transplantation in Irritable Bowel Syndrome: A Systematic Review and Network Meta-Analysis. Nutrients 2024; doi:10.1136/gutjnl-2016-312513 PubMed 38999862
4. Efficacy of Probiotics in Irritable Bowel Syndrome: Systematic Review and Meta-analysis. Gastroenterology 2023; doi:10.1053/j.gastro.2023.07.018 PubMed 37541528
5. Outcome-Specific Efficacy of Different Probiotic Strains and Mixtures in Irritable Bowel Syndrome: A Systematic Review and Network Meta-Analysis. Nutrients 2023; doi:10.3389/fcimb.2022.859967 PubMed 37686889
6. Probiotics for management of functional abdominal pain disorders in children. The Cochrane database of systematic reviews 2023; doi:10.1002/14651858.CD010972.pub2 PubMed 36799531