What is the FODMAP elimination and reintroduction diet?

The low-FODMAP diet is frequently misrepresented as a list of foods to avoid permanently. It isn't. It's a structured three-phase diagnostic protocol — the goal of which is to identify your specific triggers and then reintroduce everything else. Done correctly, most people end up eating a much broader diet at the end than they expected.

Phase 1: Elimination (2–6 weeks)

All high-FODMAP foods are removed from the diet. This is not a gentle reduction — it's a thorough removal, intended to create a clean baseline. Most people see a significant reduction in symptoms within 2–4 weeks if FODMAPs are a driver of their IBS.

The elimination phase should not be extended indefinitely. A prolonged low-FODMAP diet reduces dietary diversity and can affect the gut microbiome. The purpose of this phase is to confirm that FODMAPs are relevant to your symptoms — not to remain in it long-term.

Phase 2: Reintroduction (6–8 weeks)

Each FODMAP subgroup is reintroduced systematically, one at a time, in gradually increasing amounts over three days. After each test, you return to the baseline elimination diet for a few days to clear any symptoms before testing the next group.

This is the most important phase — and the one most people skip or do badly. Without systematic reintroduction, you don't know which specific FODMAPs trigger your symptoms. You might be avoiding garlic and wheat when your only real trigger is lactose. The elimination phase tells you that FODMAPs matter; the reintroduction phase tells you which ones.

Tracking is essential here. You need to log exactly what you ate, when, at what quantity, and what symptoms followed and when. Without a log, it's nearly impossible to draw reliable conclusions from a 6-week reintroduction process.

Phase 3: Personalisation

Once you know your triggers, you build a personalised diet that avoids only the foods that cause you specific problems. This is not a restricted diet — most people find they can eat the majority of foods freely, and only need to be careful about one or two specific FODMAP groups or serving sizes.

It's worth working with a dietitian trained in the low-FODMAP diet for phases 1 and 2. The reintroduction process is nuanced, and having professional guidance significantly improves outcomes compared to attempting it from online resources alone.