How the Low FODMAP Diet Works – The Re-challenge Phase

The re-challenge phase is an exciting time as this is when, after eliminating all the high FODMAP foods, you can start learning about the foods that trigger you. After completing this phase, you will know a lot about which foods you can re-introduce in your diet, which ones you can have in small amounts or only occasionally, and which ones to avoid, and maintain good symptom control.

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5 Key Things to know about the Re-challenge Phase

1. There is no set protocol for this phase, only generic guidelines

As soon as symptoms have considerably improved on the strict phase of the low FODMAP diet, you are ready to re-challenge foods that you avoided during the elimination phase: the high FODMAP foods. There are different approaches to this phase, and an expert dietitian can help you determine the best approach according to your symptoms, anxiety level, and other considerations.

Researchers are still studying the best way to carry out the challenges but have identified some key factors that are important to the success of this phase. I have outlined these guidelines below.

2. Challenge each FODMAP subgroup separately

Over the course of 6 to 8 weeks, you will be able to challenge all the major FODMAP categories (and subcategories) one at a time and find out which foods may trigger symptoms. This is essential, as tolerance to each category may vary and each has distinct physiological effects in the gut.

During each challenge it is important to continue eating a low FODMAP diet – the same as during the elimination phase – with the exception of the new food or foods introduced each week. This allows you to isolate each type of FODMAP and find the trigger of any potential symptoms without a doubt.

4. Record symptoms

It is key to record the types of symptoms one may experience during each challenge and their severity. A small amount of onions or black beans may not cause any or only mild symptoms, but bigger portions may cause severe symptoms. Keeping a food and symptom diary will help track these differences in response to food challenges and allow you to make informed decisions. For example, you may find that eating ½ an avocado causes a moderate degree of bloating and decide to eat it only when at home and comfortable with having mild symptoms but refrain from eating it at social occasions or in restaurants.

5. Keep re-challenging problem foods 

IBS symptoms are known to wax and wane over time. Stress levels and other factors influence these changes. It is important to keep re-challenging foods that “failed” the first challenge in order to keep increasing the variety of the diet and minimize the risk of nutritional inadequacy. A food that is poorly tolerated at first may be better tolerated 3-6 months later. Reducing the dose of the food tested and/or managing stress during the time of challenging may also increase its tolerance.