The FODMAP diet for IBS
Why IBS searches lead to FODMAP
Irritable bowel syndrome (IBS) is a functional gut disorder causing bloating, pain, and altered bowel habits, without a single identifiable cause. Since the early 2010s, research from Monash University has established the low FODMAP diet as the best-evidenced dietary approach for managing IBS symptoms — roughly 3 in 4 people with IBS see meaningful improvement.
The three phases
- Elimination (2–6 weeks). Strictly avoid high-FODMAP foods across all six subtypes to establish whether symptoms improve at all. If they don't improve, FODMAPs likely aren't the main driver, and the diet should be stopped rather than continued indefinitely.
- Reintroduction (several weeks). Reintroduce one FODMAP subtype at a time, in structured amounts, while tracking symptoms — the goal is to identify exactly which subtype(s) trigger you, since most people react to only one or two of the six.
- Personalisation (ongoing). Build a long-term diet that only restricts the subtypes that actually caused symptoms, keeping everything else on the table. This is the phase people should land in — not permanent elimination.
Where SIBO fits in
Small intestinal bacterial overgrowth (SIBO) causes symptoms that look a lot like IBS — bloating, gas, discomfort — but has a specific mechanical cause: bacteria that should stay in the large intestine overgrow further up, in the small intestine. It's diagnosed with a breath test rather than by diet response, and the primary treatment is usually antibiotics or other medical intervention, not diet alone. A low FODMAP diet can reduce symptoms in the meantime by starving the overgrown bacteria of fermentable fuel, but it doesn't fix the overgrowth itself — which is why a proper diagnosis matters before assuming diet alone will solve persistent symptoms.
NZ resources
Health NZ Auckland's dietetic service publishes a free patient guide covering the elimination phase in detail: Low FODMAP Diet — Phase 1. See also our conditions overview for links to Healthify Hā Hauora's general FODMAP information.
Once you know which subtypes to avoid, use the FODMAP filter on our products page to find NZ packaged products screened against those specific subtypes, rather than an all-or-nothing avoidance list.
Frequently asked questions
How long does the low FODMAP diet take?
The elimination phase is typically 2–6 weeks — just long enough to see whether symptoms improve. It is not meant to be followed indefinitely. Reintroduction (identifying which subtypes actually trigger you) can take several more weeks, testing one subtype at a time.
Do I need a diagnosis of IBS before trying it?
A proper diagnosis first is strongly recommended, because FODMAP-triggered symptoms can overlap with other conditions (including coeliac disease, inflammatory bowel disease, and SIBO) that need different management. See your GP before starting.
What is SIBO, and is it the same as needing a low FODMAP diet?
SIBO (small intestinal bacterial overgrowth) is a specific condition where bacteria that normally live in the large intestine overgrow in the small intestine, causing IBS-like symptoms. It is diagnosed with a breath test, not by diet response, and is treated primarily with antibiotics or other medical treatment — a low FODMAP diet may help manage symptoms alongside that treatment, but it does not treat the underlying overgrowth.
Can I do the FODMAP diet without a dietitian?
You can start with credible resources like Health NZ's patient guide, but a dietitian is strongly recommended for the reintroduction phase — done incorrectly, people often get stuck in strict elimination far longer than needed, which can affect gut microbiome diversity and overall nutrition.