What this phase is for
Reintroduction tells you which FODMAP groups your gut actually struggles with. You test each group one at a time, in increasing amounts, against a low-FODMAP background diet.
By the end you will have a personal map of triggers, doses, and safe foods. That map is the foundation for a flexible long-term diet. Most people discover they tolerate more than they expected.
How long it takes
Plan for 6 to 8 weeks. Each FODMAP group is tested over 3 days, followed by a 3-day washout to let any symptoms clear.
There are 6 FODMAP groups to work through (fructose, lactose, fructans, GOS, sorbitol, mannitol), so the full sequence often runs closer to 9–10 weeks if you do them all back-to-back. You can take longer between challenges if you need extra washout days. There is no rush.