Elimination phase explained

The elimination phase is the first part of the low FODMAP diet. The purpose of this phase is to swap all high FODMAP foods in your diet with low FODMAP portions or alternatives. This usually needs to be done for a period of 2-6 weeks under the supervision of a registered dietitian. You’ll work together with your dietitian to decide the length of your elimination phase. It will usually be based on a variety of factors including your individual symptoms and medical history. [1]

Before the elimination phase

Before beginning the elimination phase your dietitian will ask about your eating habits, lifestyle and symptoms. You'll discuss the purpose, goals and limitations of the low FODMAP diet. They will usually supply you with a list of high FODMAP foods to avoid and portions to limit for the length of your elimination phase. More importantly, they'll advise you on all the foods you can still eat including those which are FODMAP free or contain only small amounts of FODMAPs.

The nutritional knowledge of a dietitian is especially beneficial to anyone who already eats a limited diet such as vegans*, coeliacs or those with multiple allergies.

Your dietitian may;

• provide written guides, lists and leaflets
• refer you to useful resources such as the Monash FODMAP blog
• encourage you to download the Monash app or the FODMAP app by Food Maestro (only available in the UK)
• ask you to keep a food and symptoms diary to monitor your progress.

Ideally, you'll be offered a follow-up appointment towards the end of your elimination phase to see how it’s all going and help you progress to the crucial reintroduction phase of the diet. [2, 3, 4]

During elimination phase

During your elimination phase you will;

• refer to the Monash app (or the resources your dietitian recommends) when shopping, planning and preparing meals
• using these lists you'll learn to avoid or reduce all high FODMAP foods in your diet
• eat only low FODMAP foods or low FODMAP portions of moderate-high FODMAP foods for the length of your elimination (4 weeks on average)
• spend time reading labels and becoming familiar with the ingredients in your food
• monitor your food, symptoms and progress in a diary or app

People sensitive to FODMAPs will usually notice a significant relief in their IBS symptoms during this time. This improvement is crucial because it shows that you are sensitive to FODMAPs. Crucially, it also allows you to experience your personal baseline level of symptoms. You’ll then use this baseline as your guide during the second phase of the diet as you reintroduce foods and assess your reactions.

After elimination phase

Ideally you'll have a follow up appointment with your dietitian. This gives you the opportunity to ask any niggling questions that came up during elimination. It also allows the dietitian to monitor your progress and prepare a plan for moving into the reintroduction phase.

Once you're happy with your overall baseline symptoms you'll begin the reintroduction phase. Preferably this should begin immediately following your elimination phase. If this is not the case for you then your dietitian is the only person that can advise you how to proceed.

It’s really important for your overall physical and mental health that the restricted elimination phase of the diet is temporary. Many high FODMAP foods are healthy and beneficial to us and our digestive systems. They are sources of essential nutrients, dietary fibre, pre and probiotics. This means they should only be eliminated for as long as necessary to determine that FODMAPs are an issue for you and see that your symptoms have improved.

Unnecessarily restricting foods for an extended period of time can also have a negative impact on your mental health and social life. Any initial physical benefits you may feel from restricting FODMAPs in your diet will likely be undone if continued indefinitely. There is the potential to severely impact your gut health and microbiome and this continues to be a genuine concern to the research dietitians working in the field of FODMAPs. [5, 6]

* I’m not in any way suggesting that a vegan diet is “limited,” I believe it’s far from it. However, from a purely dietary point of view, we are choosing to exclude certain food groups. Many animal products are FODMAP safe foods that people typically rely upon during the elimination phase of a low FODMAP diet.

Confused about elimination phase? Check out the other posts in this series.

Pop your elimination phase questions in the comments box below.