Person writing up a meal plan in a notebook next to a pair of glasses

The 3 Phases of the Low Fodmap Diet

Do you know what the low fodmap diet phases are? Did you know that the low fodmap diet even had individual phases to it? The three phases are the fodmap elimination phase, challenge phase and reintroduction phase.

If you have heard of the low fodmap diet, you may assume it is a “diet” in the traditional sense such as Paleo, Atkins etc. However, the low fodmap diet is actually more of a process and the phases are listed below.

  • Elimination phase
  • Challenge phase
  • Re-introduction phase

The diet is meant to pinpoint certain fodmap food triggers if there are any. It isn’t really meant to be a diet in the traditional sense at all!


Before we dive in, let’s quickly talk about fodmap basics first. Fodmaps are different types of sugars that are rapidly fermented by the bacteria in our gut. The byproduct of this process is gas production. Fodmaps can also draw water into the intestine.

For many people, fodmap fermentation is a harmless process. Others, however, may experience abdominal pain, bloating, excessive gas and even diarrhea.

There are several different categories of fodmaps and there are many different foods within each category. The main fodmap categories are listed here.

  • Lactose
  • Fructose
  • Fructans
  • Galactooligosacharrides/GOS
  • Polyols

Generally, if someone is sensitive to fodmaps, they are more sensitive to one or two of these groups than the others. The tricky part about this is we don’t know which ones are causing the trouble.

Backing up a bit, we don’t even know if they are sensitive to fodmaps in the first place. This is where the phases of the diet come in.   

A woman holding her stomach with a look of pain on her face

Low Fodmap Elimination Phase

The first phase of the diet, called the elimination phase, acts as “test” to determine if the diet may be helpful for that individual. We cannot assume that it will be beneficial. While it is helpful to many people with GI issues, it is not helpful to all.

To determine this, all high fodmap foods are eliminated for two to six weeks. Hence the name “low fodmap elimination phase”. If symptoms subside (less bloating, abdominal pain, excessive gas for example), then we know that at least one group of fodmaps was contributing to those symptoms.

If no symptom relief was experienced, then we know that fodmaps are likely not the culprit and other treatments should be pursued.

Low Fodmap Challenge Phase

Now, if the elimination phase did improve symptoms within the recommended time frame, then it is time to implement the challenge phase. During this phase, a low fodmap diet is continued in the background, while each fodmap group is “challenged”.

This is done by consuming a small amount of one food from one group, working your way through the groups one at a time. A food can be challenged over the course of several days, each day slightly increasing the amount consumed. See example below.

Lactose Challenge:

  • Day 1: 1/3 cup cow’s milk
  • Day 2: 2/3 cup cow’s milk
  • Day 3: 1 cup cow’s milk

By slowly increasing the amount of food consumed, a personal tolerance level may be identified. Sticking with the milk example – some who are sensitive to lactose may not be able to tolerate any milk at all.

Others may notice that they can comfortably tolerate a certain amount, 1/3 cup for example, but may not be able to tolerate much more than that.

Someone pouring milk from a carafe into a glass that is sitting on a table sop with the sun setting in the background

This phase should paint a picture of which fodmap groups are troublesome. Symptoms will inevitably occur during the challenge for that group. Once all of the groups have been challenged, it is time to move on to the last phase called the re-introduction phase.  

Low Fodmap Re-introduction Phase

At this point, it should be pretty clear which fodmap groups are symptom triggers. The goal of the re-introduction phase is to re-introduce as many high fodmap foods as possible. This includes foods from determined non-trigger fodmap groups. It also includes foods from trigger groups in amounts that seem to be tolerated. This will ensure nutritional adequacy and a varied diet.


To recap, the low fodmap diet has three phases to it. The elimination phase – all high fodmap foods are eliminated for a period of time. The challenge phase – one food from each fodmap group is challenged in small, increasing portions to determine tolerance.

Lastly, the re-introduction phase – diet is liberalized to include foods that were not problematic while continuing to avoid foods that were.

The low fodmap diet can be a useful process for some but should be viewed as a process, rather than a long term diet. Due to the large number of high fodmap foods, following a low fodmap diet is not nutritionally adequate long term.

It is also more restrictive than most people need even if they are sensitive to some fodmap groups, because they are likely not sensitive to all. It is important to work with a qualified GI dietitian throughout the process to guide and support you.

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As always, thanks for reading!