The 3-day challenge window
Each FODMAP challenge takes 3 days. You'll eat a test food on day 1, then track symptoms for 2 more days while returning to low-FODMAP meals.
Why 3 days? Some symptoms show up immediately. Others take 24–48 hours. This window gives you time to see the full picture.
If you have symptoms, wait until they settle before starting the next challenge. If you feel fine after 3 days, that FODMAP group is likely safe for you.
Start small, then increase
Monash recommends testing each FODMAP group at 3 serving sizes: small, medium, and large. Start with the smallest serve. If you tolerate it, try a medium serve 3 days later, then a large serve 3 days after that.
For example, when testing fructans, you might start with 1 slice of wheat bread, then 2 slices, then a full bowl of pasta. This helps you find your threshold, the amount you can eat without symptoms.
If a small serve triggers symptoms, you know that FODMAP is a problem food. Skip the larger serves and move to the next group.