Something that confuses people about the low FODMAP diet is the length of time you have to be on it. Another common confusion is what each phase of the diet involves. While I’ve heard many incorrect ideas along the way, the two most common misconceptions I hear are:

  1. You follow the low FODMAP diet for 6-8 weeks and then reintroduce all of the foods you used to eat and go back to your normal diet.
  2. Once you start on a low FODMAP diet, you’ll be on it forever.

But neither of these are correct.

Firstly, most people who find that a low FODMAP diet helps to manage their Irritable Bowel Syndrome (IBS) can’t go back to how they used to eat because they are intolerant to some of the FODMAPs. Secondly, a strict low FODMAP diet isn’t meant to be followed forever because the gut microbiota (the types and amounts of bacteria in your gut) changes on a low FODMAP diet.

So to clear up confusion, let’s talk about the 3 phases of the low FODMAP diet so you’ll fully understand how the process works and can then work out what you need to do next.

3 phases of the Low FODMAP Diet - A Less Irritable Life


Phase 1. Restriction Phase (also called the ‘Elimination Phase’)

What is the purpose of the Restriction Phase?

The restriction phase has only one purpose… to determine whether your IBS symptoms improve when the amount of FODMAPs in your diet is decreased. If your symptoms do improve on a low FODMAP diet, this indicates that FODMAPs are a likely trigger for your IBS.

Note: this phase is commonly called the ‘elimination phase’, but you can’t actually eliminate all FODMAPs from your diet. The goal is to restrict and lower FODMAPs. That’s why it’s called the low FODMAP diet.


What does the Restriction Phase involve?

This is the most difficult phase of the low FODMAP diet since it takes lots of effort to adjust regular eating habits. FODMAPs are found in many different types of foods across all of the five food groups, so it’s likely you’ll need to adjust most of your usual meals, snacks and drinks.

Given the complex nature of FODMAPs and how restrictive the diet is, it’s best to undertake the diet under the guidance of a qualified nutrition professional. There’s two reasons for this:

  1. You need to be certain you’re getting accurate and up-to-date information about FODMAPs so you don’t waste your time eating the wrong foods.
  2. You need to make sure that the food items you’re still eating are suitably balanced to meet your nutritional needs.


How does the Restriction Phase affect your IBS symptoms?

Ideally, your symptoms will become little more than an irritation and you’ll find it much easier to go about your daily tasks without fear of your IBS symptoms occurring. But in reality, you’re likely to continue experiencing some symptoms but at a much lower intensity than you did before. It takes time for the body to adjust, including the way that your nervous system responds to normal gastrointestinal movements.

If however the low FODMAP diet doesn’t work for you, your symptoms will remain almost the same as before you started. Clinical studies have found that 75% of IBS sufferers experience symptom relief when following a low FODMAP diet, which means it won’t be successful for everyone.


How long does the Restriction Phase take?

It’s generally recommended to follow the low FODMAP diet as strictly as possible for about 6-8 weeks, which is normally enough time to see whether the diet is improving your IBS symptoms. Some people will however need longer so that other factors can being taken under consideration, or if their body needs longer to adjust.


Who needs to complete the Restriction Phase?

Everyone who wants to trial the low FODMAP diet must complete this phase. You shouldn’t proceed to the next phase unless you have first gotten your symptoms under control, or a nutrition professional advises you to do so.


Do you need to do anything before you start the Restriction Phase?

The low FODMAP diet isn’t meant for everyone. It’s a medical therapeutic diet designed to help people manage the symptoms of IBS. So before you start, it’s essential that your doctor rules out other potential causes of your gastrointestinal symptoms so that other issues aren’t overlooked.

It’s also essential you get correct information about FODMAPs so you don’t waste your time thinking that you’re doing it right, but actually making mistakes. The best way to do this is to book an appointment with a nutrition professional who is a FODMAP specialist before you start. You might also like to monitor your abdominal symptoms and bowel movements for a week or so too.

Further reading:


Phase 2. Tolerance Testing Phase (also called the ‘Reintroduction Phase’)

What is the purpose of the Tolerance Testing Phase?

This phase tests your personal tolerance levels to individual FODMAPs. You need to do this to work out which FODMAPs you’ll need to continue restricting in the future to keep your IBS under control. It will also tell you which FODMAPs you don’t react to and so can begin eating once again.

Note: this phase is generally called the ‘reintroduction phase’, however many people misinterpret this to think it means you return to your normal eating habits. But that is definitely not what this phase is about. That’s why I prefer to describe it as FODMAP Tolerance Testing.


What does the Tolerance Testing Phase involve?

This phase involves systematic testing of individual FODMAPs to determine whether or not they trigger your IBS symptoms. You gradually work your way through all of the FODMAPs, one by one, eating carefully selected foods that contain only one type of FODMAP. You also test these foods at different portion sizes to determine your sensitivity levels.

Essentially this is a science experiment to see how your body reacts. IBS isn’t a straightforward condition and can be triggered by different things in different people, so you’ll likely find some FODMAPs are very problematic for you while others won’t cause any issues.


How does the Tolerance Testing Phase affect your IBS symptoms?

This is a little hard to predict since everyone is different. But at some point you’re likely to experience major IBS symptoms when you test FODMAPs that you’re intolerant to. This can be distressing and inconvenient, especially after finally getting your symptoms under control, but you do need to do it.


How long does the Tolerance Testing Phase take?

This phase takes most people around 10-12 weeks to complete because:

  1. There are a lot of tests to do and you can only do one test per week.
  2. Sometimes you need a longer recovery time than the required 3 days if you’ve had a very bad reaction or if you’re mentally exhausted from the challenge process (it happens).
  3. Sometimes you need to temporarily stop testing because of other life factors that could interfere with the results, such as illness, stress or other possible IBS triggers.


Who needs to complete the Tolerance Testing Phase?

Everyone who found that the first phase helped their IBS symptoms must do tolerance testing to work out which foods are their real issue. Once you’ve done this, you can get back to eating as normal a diet as possible and not restrict your food choices any more than is absolutely necessary.

Try to keep in mind that while it can be scary making yourself eat foods that might make you sick, after you’ve done the test don’t have to eat any of the foods you react to. It’s also helpful to focus on the fact that you aren’t likely to react to all FODMAPs, so this process is really about helping you to identify the foods you’re going to be able to eat again.


Is there anything you need to do before you begin the Tolerance Testing Phase?

You need to successfully complete the restriction phase so that your symptoms have stabilised. However if your symptoms are still very unstable, you should seek advice to determine whether other factors might be triggering your IBS symptoms and need to be managed.

The other critical thing to do is get accurate information about testing FODMAPs so you don’t waste your time. The best way to do this is to seek the help of a qualified nutrition professional who can provide you with the information you need. They should also assess your symptoms to make sure that you are indeed ready to begin this phase or whether other changes are needed first.


Phase 3. Maintenance Phase (generally referred to as a ‘Modified Low FODMAP Diet’)

What is the purpose of the Maintenance Phase?

The purpose is to get you back to eating as normally as possible and to expand your food choices. Once you’ve done all of your testing, you’ll know which FODMAPs you’re most sensitive to and need to continue restricting. But you’ll also know which FODMAPs you don’t react to and so can begin eating them again. Essentially you can view this phase as getting as closely to normal as possible.


What does the Maintenance Phase involve?

First let’s look at what the maintenance phase doesn’t involve. It doesn’t involve you going back to eating the way that you used to. If you’ve progressed this far, there will be some foods that trigger your IBS and will need to be restricted so your symptoms don’t return.

Instead this phase involves developing a modified dietary approach based on your tolerance testing to include foods from FODMAP categories that you didn’t react to. But you’ll still need to restrict food from the FODMAP categories that you reacted badly to.


How does the Maintenance Phase affect your IBS symptoms?

In theory, your IBS symptoms should remain minimal provided that you only add back foods from FODMAP categories that you didn’t have problems with. In reality, as you get more confident with your food choices, you’re likely to start pushing the boundaries on your tolerances to see just how much of a particular FODMAP (or total FODMAP load) you can get away with. This unfortunately will create some mistakes and symptoms, but overall things should be much better than before.


How long does the Maintenance Phase take?

This is an ongoing phase with no set end point. However, IBS triggers and food intolerances can change over time, so it’s recommended that you periodically test your tolerance to the FODMAPs you reacted badly to so you can see if your tolerances have improved. The goal here is to eat and live as normally as possible with the least restrictions you can get away with.


Who needs to complete the Maintenance Phase?

Everyone who’s progressed through the first two phases needs to modify the low FODMAP diet to suit their needs. It’s important that you don’t continue to restrict your diet any more than is necessary since it can lead to nutrient deficiencies. Also, the more FODMAPs you can return to your diet without triggering symptoms, the healthier your gut microbiota is likely to be.


Is there anything you need to do before you begin the Maintenance Phase?

You need to complete the first two phases before you progress to this one.

It’s also wise to discuss your tolerance testing results with your FODMAP specialist, who can advise you of which foods you will need to continue restricting and which foods you can begin eating again.


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