Reintroducing FODMAPs, step by step

Reintroduction is the second phase of the low FODMAP diet. Once your symptoms have settled on the strict phase, you bring the FODMAP groups back one at a time, in small and then larger amounts, while the rest of your diet stays low FODMAP. The aim is to learn which groups bother you and how much of each you can eat, so you can go back to eating as widely as possible. The British gastroenterology guideline recommends reintroducing FODMAPs according to tolerance, with a trained dietitian.^[1]

Why it matters

The strict phase is a test, not a way to eat for good. Reviews of the diet describe three stages, restriction, reintroduction and personalisation, with reintroduction there to find the foods that trigger your symptoms so you can then eat a less restrictive, more varied diet.^[2]

Variety matters for more than enjoyment. In one small trial of 50 people with IBS, fibre intake fell from about 33 g to 21 g a day on the strict diet and rose again to about 27 g a day after FODMAP foods were brought back, while the improvement in symptoms held.^[3] The British guideline notes that most trials have only studied the strict phase, so the effect of reintroduction itself is less certain.^[1]

When to start

Start once your symptoms have clearly improved, usually after 2 to 6 weeks of the strict phase. If they haven’t improved after about 4 to 6 weeks, reintroduction won’t tell you much: go back to your doctor or dietitian rather than restricting further. Our guide to the low FODMAP diet covers the strict phase.

How to test one group

1. Keep everything else low FODMAP. Only the food you are testing should change.
2. Pick a food that contains mainly one group. If it has two, you won’t know which one caused a reaction.
3. Start with a small amount, then eat a larger amount on the following days if you feel fine.
4. Write down what you ate, how much, and how you felt over the next day.
5. If symptoms come back, stop the test and wait until you feel settled again before testing the next group.
6. Move on to the next group, even if the last one went well. Keep that food out until you have tested everything, so results don’t mix.

A dietitian can give you a plan with exact foods, amounts and timings that fit your symptoms and the foods you like to eat.

Foods that make clean tests

These foods carry mainly one FODMAP group in our data, which makes them useful test foods. Each food page shows the amount up to which it stays low.

Group	Example foods
Fructans	Pasta (wheat)
GOS	Lentils
Lactose	Milk
Excess fructose	Asparagus
Sorbitol	Nectarine
Mannitol	Mushrooms

Some everyday foods carry more than one group. Onion, for example, is high in fructans with some GOS, so it’s better eaten once you’ve tested both groups separately. Garlic and onion are worth testing on their own later, since they turn up in so many dishes.

If symptoms come back

A reaction is a result, not a failure. It tells you that group, at that amount, is a trigger for you right now. Note the amount that caused symptoms and the amount before it that didn’t: that line is what you’ll use in the next phase.

After reintroduction: personalise

Bring back every group you tolerated, and limit only the groups and amounts that caused symptoms. Most people end up avoiding far fewer foods than in the strict phase. Remember that FODMAPs from several foods in one meal add up, so a food you tolerate on its own may be harder to manage alongside others from the same group. The US guideline recommends the diet as a limited trial,^[4] and the British guideline advises that a trained dietitian supervises it.^[1]

How Fodmi helps

Reintroduction depends on good notes. Fodmi is an iPhone app that makes them easier: you log a meal with a photo, your voice or text, see its estimated FODMAPs across the six groups, and get a check-in a few hours later on how it sat. Over a few weeks you can see which foods line up with bad days, and share a PDF report with your doctor or dietitian. Fodmi’s amounts are estimates from published food composition data. It doesn’t replace a dietitian’s plan.