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How to reintroduce FODMAPs

Updated October 5, 2026 by Kamal Nasir

In the reintroduction phase you stay on your low FODMAP diet and test one FODMAP group at a time, eating a food rich in that group on 3 days in a row with a bigger portion each day, while recording your symptoms. Monash University, whose researchers developed the diet, recommends a 2 to 3 day break back on low FODMAP foods between challenges, and says the whole phase takes most people around 6 to 8 weeks. Monash recommends doing it with a dietitian who can interpret the results.

General information, not medical advice. How these guides are made.

Where reintroduction fits

Monash describes the diet in three steps. Step 1 swaps high FODMAP foods for low FODMAP alternatives for 2 to 6 weeks. If symptoms improve, Step 2, reintroduction, works out which FODMAPs you tolerate and which trigger symptoms. Step 3 builds a personalized long-term diet that restricts only what you need to.

If your symptoms did not improve in Step 1, Monash says your IBS may not be sensitive to FODMAPs, and other approaches are worth discussing with your doctor. It estimates that about one in four people with IBS fall into that group.

The FODMAP groups you test

Monash groups FODMAPs as below. Each subgroup is reintroduced separately, because your tolerance to each can be different.

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IBS Tracker Food Diary: Fennel

IBS food diary and symptom tracker

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How a 3-day challenge works

Monash research dietitian Dr. Jane Varney sets out these steps, to be adjusted by your dietitian:

Which order to test in

Monash says there is no set order. Some people start with a FODMAP they expect to tolerate, to build confidence. Others start with one they suspect, to get a clear answer sooner. Others start with the FODMAP in a staple food, for example wheat pasta to test fructans in grains, so they know early whether it can stay in their everyday diet.

Monash revised its recommended challenge foods after retesting them in its laboratory, because the FODMAP content of some foods differed from earlier tests. Check current guidance with your dietitian rather than relying on an old printed list.

What to record during challenges

For each challenge day, note the food and the portion, the time you ate it, each symptom with its time and severity, your bowel movements, and your stress level, which the Monash diary also records. Write down the break days too, so you can see whether symptoms had settled before the next test began. Monash advises starting each challenge only when symptoms are well controlled, so also note anything unusual on a challenge day, such as a stressful event or an illness, for your dietitian to weigh.

After the challenges

Monash recommends having a dietitian interpret your responses. In Step 3, well tolerated foods return to your diet, and poorly tolerated ones are limited only to the level that keeps symptoms under control, which is not always the same as cutting them out. Tolerance can change, so Monash suggests trying poorly tolerated foods again after a few months.

Safety first

The FODMAP diet is meant for people with medically diagnosed IBS. Monash says not to follow it without a diagnosis, because conditions such as celiac disease, inflammatory bowel disease and bowel cancer can cause similar symptoms. The NIDDK lists bleeding from your rectum, bloody stools or stools that are black and tarry, weight loss and anemia as symptoms that may point to a health problem other than IBS, and the NHS, the UK health service, adds a hard lump or swelling in your belly. See a doctor about any of these rather than waiting for a challenge to finish.

Tracking reintroduction

A paper diary works, and the Monash FODMAP app has its own reintroduction diary. Fennel, an IBS food diary for iPhone, has a guided reintroduction program that schedules challenge days and rest days, records what happened on each, and drafts a reading you can accept or overrule. Phase lengths appear as ranges because its sources state them as ranges. The program is part of Fennel Pro, and it does not replace your dietitian.

Questions people ask

How long does FODMAP reintroduction take?

Monash University says most people take around 6 to 8 weeks. Each challenge lasts 3 days, with a 2 to 3 day break on low FODMAP foods before the next one.

Do I stay low FODMAP during reintroduction?

Yes. Monash advises staying on your Step 1 low FODMAP diet throughout, so the only change on a challenge day is the food being tested.

Do I have to avoid a FODMAP I reacted to for good?

Not necessarily. In Monash's Step 3 you limit a poorly tolerated FODMAP only as far as keeps symptoms settled, and because tolerance can change, Monash suggests retesting after a few months.

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