IBS (Irritable Bowel Syndrome) — NZ Condition Guide | KiwiMeds

What is IBS?

Irritable bowel syndrome (IBS) is a common gut disorder that affects the large intestine (colon) and causes a group of symptoms that occur together — abdominal pain, bloating, and changes in bowel habits (diarrhoea, constipation, or both). IBS is a functional disorder — there is no visible damage or disease in the bowel, but the way the gut works is altered. It affects around 10–15% of New Zealanders and is more common in women and younger adults. IBS does not increase the risk of bowel cancer.

Symptoms

IBS symptoms include cramping abdominal pain (often relieved by a bowel movement), bloating and excess wind, diarrhoea, constipation, or alternating between the two, mucus in stools, a feeling of incomplete bowel emptying, and urgent need to go to the toilet. Symptoms are often triggered by eating, stress, or hormonal changes. Many people with IBS have periods of normal bowel function alternating with flares of symptoms. Symptoms that warrant urgent review by a doctor include blood in stools, unintentional weight loss, symptoms starting after age 50, or waking from sleep with symptoms.

Causes and Risk Factors

The exact cause of IBS is not fully understood. It involves changes in gut motility (how quickly food moves through), increased gut sensitivity (pain signals from the gut), changes in gut bacteria (the microbiome), brain-gut axis dysfunction, and psychological factors (anxiety, depression, stress). IBS often starts after a gut infection — this is called post-infectious IBS. Risk factors include being female, under 50, having a history of anxiety or depression, and stressful life events.

Diagnosis

IBS is diagnosed using the Rome IV criteria — a set of symptom-based criteria. There is no specific test for IBS, but your GP may order blood tests, stool tests, and sometimes colonoscopy to rule out other conditions such as inflammatory bowel disease, coeliac disease, or colorectal cancer. If you are over 50 and have new bowel symptoms, a colonoscopy is recommended to rule out colorectal cancer.

Treatment in New Zealand

IBS management in NZ is tailored to your main symptoms. Dietary changes are key — the low-FODMAP diet (reducing fermentable carbohydrates that trigger symptoms) has the best evidence and can be done with guidance from a dietitian. Fibre supplements (psyllium) help some people. Medications include antispasmodics (mebeverine — funded by Pharmac) for pain and cramping, loperamide for diarrhoea-predominant IBS, and laxatives for constipation-predominant IBS. Psychological therapies (CBT, gut-directed hypnotherapy) are very effective, particularly for stress-related IBS.

NZ-Specific Information

Dietitian referrals are available through your GP for low-FODMAP guidance. Pharmac funds several IBS medications. The IBS Network and Crohn’s and Colitis NZ provide support resources. Mindfulness and stress management programmes are widely available online and through community health services.

Frequently Asked Questions

Is IBS the same as inflammatory bowel disease (IBD)? No — IBS is a functional disorder with no bowel inflammation or damage. IBD (Crohn’s disease, ulcerative colitis) involves actual inflammation of the bowel wall and is a separate, more serious condition. Can IBS be cured? IBS is a long-term condition, but symptoms can be managed very effectively with the right approach. Many people find their symptoms improve significantly over time. Should I try the low-FODMAP diet? Yes — it helps about 70% of people with IBS. Ideally do it with dietitian guidance.

Supplements That May Support Management

⚠️ Important: The supplements listed below have varying levels of clinical evidence. They are not a substitute for prescribed medications and should only be considered as adjunctive support under the guidance of a qualified healthcare professional. Always inform your GP or pharmacist before commencing any supplement, as interactions with prescribed medicines are possible.

• Probiotics (multi-strain or species-specific) — Multiple randomised trials support the use of probiotics in IBS for reducing bloating, flatulence, and overall symptom burden. Lactobacillus and Bifidobacterium species have the strongest evidence. Benefit is strain-specific; products with demonstrated clinical trial evidence should be selected.
• Peppermint Oil (enteric-coated capsules) — Peppermint oil has smooth muscle antispasmodic properties via calcium channel antagonism in the gut. Multiple meta-analyses support its efficacy for IBS-related abdominal pain and spasm. Enteric-coated formulations (e.g., Colpermin, IBgard) are required to avoid oesophageal reflux as a side effect.
• Psyllium Husk (soluble fibre) — Soluble fibre from psyllium is the most evidence-supported dietary supplement for IBS overall, improving stool consistency and frequency in both constipation-predominant and diarrhoea-predominant IBS. Starting slowly (1 teaspoon/day, titrating up) reduces initial bloating.
• L-Glutamine — Glutamine is the primary fuel for enterocytes (intestinal lining cells) and supports gut barrier integrity. Preliminary trial evidence supports its use in diarrhoea-predominant IBS (IBS-D) for reducing intestinal permeability and symptom severity.
• Magnesium Oxide — For constipation-predominant IBS (IBS-C), magnesium oxide (250–500 mg at night) acts as an osmotic laxative supporting stool frequency without the dependence risk of stimulant laxatives.

Relevant Vaccinations

Individuals living with IBS (irritable bowel syndrome) may benefit from the following vaccinations. Please discuss your vaccination status with your GP or practice nurse, as eligibility and funding through the New Zealand National Immunisation Schedule may apply.

• Influenza (annual) — Viral gastroenteritis and other illnesses can trigger IBS flares. Annual influenza vaccination reduces illness burden.
• COVID-19 — Post-COVID gastrointestinal dysfunction is increasingly recognised as a precipitant of new-onset IBS. Maintaining vaccination may reduce this risk.

Dietary Guidance

Evidence-based dietary modifications play a meaningful role in the management of IBS (irritable bowel syndrome). The following foods are generally recommended as part of a balanced, condition-appropriate diet. A referral to a registered dietitian may be beneficial for personalised nutritional planning.

• Low-FODMAP dietary approach (under dietitian guidance) — A low-FODMAP diet (reducing Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols) is the most evidence-based dietary intervention for IBS, with 50–80% of patients demonstrating meaningful symptom improvement. This is a structured therapeutic diet that should ideally be supervised by a registered dietitian.
• Soluble fibre foods (oats, psyllium, carrots, bananas) — Soluble fibre softens stool without excessive fermentation, improving symptoms in IBS-C. Insoluble fibre (bran) can worsen bloating and is generally avoided in IBS.
• Fermented foods (kefir, yoghurt with live cultures) — Low-lactose fermented dairy with live cultures supports gut microbiome diversity and may reduce IBS symptom severity.
• Ginger — Ginger has prokinetic and anti-nausea properties that may help with nausea and upper GI symptoms associated with IBS. Can be consumed as tea, fresh, or in supplement form.
• Limit: caffeine, alcohol, fatty foods, artificial sweeteners (sorbitol, xylitol) — These are well-recognised IBS triggers. Artificial sweeteners are high-FODMAP fermentable compounds; caffeine and alcohol stimulate intestinal motility and can worsen diarrhoea-predominant symptoms.

Related Conditions & Medications

Related conditions: Crohn’s Disease, GERD.