5. How does the low FODMAP diet work?

In this lesson we’ll explain the different stages of the low FODMAP diet.

By Laura Tilt

The low FODMAP diet limits foods that can trigger IBS symptoms and involves three different stages. Let’s look at each.  

Stage 1 – Elimination: 2-6 weeks

In the elimination stage you will remove as many high FODMAP foods from your diet as possible and replace them with low FODMAP alternatives. Starting FODMAP elimination can feel overwhelming, as many everyday foods (like bread, pasta, onion and milk) are high in FODMAPs. You might wonder what you can eat during this stage.   

Don’t worry – we're here to help. As well as delivering some of your meals (certified low FODMAP) we’ll be using this prep week to help you plan the rest of your diet. We’ll be sharing lists of the high FODMAP foods you need to avoid, and the low FODMAP alternatives you can replace them with. We’ll also be giving you tips to ensure your diet stays balanced and includes all food groups during elimination.  

Most people need a little time to plan meals, shop and sort their kitchen cupboards before they get started. Once you're feeling ready, you can begin FODMAP elimination.  You’ll follow this stage for 2-6 weeks and monitor your symptoms during this time. If they improve, you’ll then move onto stage 2, reintroduction.   

Stage 2 – Reintroduction: 8-12 weeks

If your symptoms improve during the elimination stage, this suggests that some high FODMAP foods are a trigger for you.   

The next step – reintroduction – will help you determine which FODMAPs you’re sensitive to. During this stage you’ll reintroduce one high FODMAP group to your diet at a time whilst continuing to track your symptoms.   

Apart from the food you are challenging, the rest of your diet will stay low FODMAP. This means you can continue eating the meals you have been eating during elimination. When you reach this stage, we’ll explain everything in more detail.    

Reintroduction can take 8-12 weeks. This can seem like a long time, but it allows for you test each FODMAP group in a small, medium and larger serving size, so you know how much you can tolerate. Once reintroduction is complete, you’ll know which high FODMAP foods are your biggest triggers, and which ones are comfortable for you to eat.   

Stage 3 – Personalisation: long term, balanced diet

In stage 3, you’ll you return to a normal, balanced diet only limiting the high FODMAPs that trigger your IBS symptoms. This should allow you to eat a wide variety of foods whilst also maintaining control of your symptoms in the long term.

What if my symptoms don’t improve during elimination?

Not everyone who has IBS will experience an improvement in their symptoms with a low FODMAP diet. If your symptoms don’t improve during the first 2-6 weeks, it’s usually a sign that FODMAPs are not a trigger for your IBS symptoms. If you have had no improvement in your symptoms, you won’t need to continue to the reintroduction stage.  

We understand that this can be disappointing, but there isn’t any way to predict who will respond and who won’t.  

If the FODMAP diet is not effective for you, you can go on to explore other non-diet therapies that might be more helpful. We’ll explain more about these options once you’ve completed your elimination trial.