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Reintroducing FODMAPs: A 7-Step Guide

I’m not gonna lie – reintroducing FODMAPs is a tricky game that takes planning, organization and, ideally, a dietitian to walk you through the process.

If you’re not working with a Monash FODMAP trained dietitian (like yours truly – shameless plug! 🫣) then hopefully you’ll find this guide helpful.

So let’s chat about why it’s important to reintroduce FODMAPs, what to expect, and how to do it successfully.

What is the reintroduction phase?

Once you’ve achieved control of your IBS symptoms during the elimination phase of the low FODMAP diet, it’s time to move on to reintroducing FODMAPs.

In the reintroduction phase, you systematically test foods one FODMAP group at a time to see how your digestive system responds. In this way, you learn which FODMAPs trigger your gut symptoms.

During the reintroduction phase, you continue to follow a low FODMAP diet so that if any symptoms appear, you can attribute that to the FODMAP group you’re challenging.

How long is the reintroduction phase?

The reintroduction phase takes about 8-10 weeks, with each FODMAP group taking a week. Although there are 5 main FODMAP groups, we break fructans and polyols down into subgroups to really zero in on specific triggers.

Specifically, fructans are broken down into 4 subcategories because fructans are made up of a wide variety of chemical structures that affect fermentation and gas production a bit differently.

So instead of fructans taking 1 week, they take about 4 weeks so you can test: 1) fructans in garlic, 2) fructans in onions, 3) fructans in wheat, and 4) fructans in fruits and vegetables. Similarly, polyols can be divided into mannitol and sorbitol.

As you can see, the fructan group encompasses a wide variety of foods that are staples in many peoples’ diets. Getting a very clear idea of which fructan-based foods trigger symptoms will help you more precisely limit your triggers and achieve better symptom control.

The duration of the reintroduction phase will also depend on your schedule, and how you respond to the food challenges. There’s no sense in testing FODMAPs when you’re on vacation, so social events may extend your reintroduction phase.

When to start reintroducing FODMAPs

Most people will feel notable improvements in their gut symptoms after about 2-4 weeks on the low FODMAP diet. One study even found that symptoms improved in as little as 1 week!

As soon as you are satisfied with your symptom control, you can start the reintroduction phase. Of course, you’ll want to consult your calendar and avoid reintroducing FODMAPs during vacations or other lengthy social events.

What to expect of the reintroduction phase

Overall, research has found that a diet low in FODMAPs improves abdominal pain, bloating, flatulence and diarrhea. The key word is “improves”. The low FODMAP diet does not cure IBS, nor will it completely eliminate symptoms.

A bit of bloating or gas is normal for everyone.   In fact, some flatulence is a good thing because it means your gut microbes are thriving which in turn benefits your gut health.

Expect some symptoms to appear when you come across a FODMAP group you don’t tolerate.  These symptoms should resolve during the break period you take between FODMAP challenges.  Most people will find a couple FODMAP groups that they’re minimally sensitive to.

Also expect to do a lot of journalling as you document which foods you test and how your symptoms respond.

Why you need to reintroduce FODMAPs

A lot of people are reluctant to reintroduce FODMAPs because they fear the return of symptoms.  This is completely understandable, and we’ll review strategies to make the process easier and less painful.

To identify which FODMAPs trigger symptoms

As an elimination diet, this is what the low FODMAP diet is all about!  With a clearer understanding of your FODMAP triggers, you’ll limit only the foods you can’t tolerate and avoid unnecessary restrictions.

To nourish your body

A lot of nutritious foods are cut out on the low FODMAP diet, which forces people to search for alternatives.  Replacing high FODMAP wheat-based foods with low FODMAP gluten-free foods is an example of where alternatives are not always the best.

In Canada, wheat must be fortified with the nutrients that were lost when it was processed. This means that wheat-based pasta, crackers and bread are decent sources of iron, folate, thiamin, riboflavin and niacin. Unfortunately, Health Canada does not require gluten-free grains to be fortified after processing, so there may be less of these important nutrients in gluten-free products.

Research on the nutritional adequacy of the low FODMAP diet is really mixed so it’s hard to draw conclusions.

In my experience as a dietitian who’s assessed thousands of peoples’ diets over the years, the more dietary restrictions a person has in place, the less diverse and nutritious their diet tends to be.

To promote gut health

Your gut microbes thrive on the FODMAPs you cut out in the elimination and reintroduction phases. So it’s not surprising that the abundance of good gut bugs like Bifidobacteria drops off during the low FODMAP diet.

Research has found that peoples’ microbiome and Bifidobacteria population improve once they start adding higher FODMAP foods back into their diet according to their tolerance level (this is called the personalization phase).

To save money

Specialty foods are expensive!  Gluten-free, certified low FODMAP, non-dairy – these foods come with premium price tags. Buying produce items out of season because they’re low FODMAP is also more expensive.

If you can discover that you don’t need only specific fruits and veggies or expensive specialty foods in your diet, then you can save your wallet some pain and resume buying original items for less. 

To enjoy restaurants and social events again

Food plays a leading role in human connection so being on a restricted diet long term can put a serious cramp in your social life. 

After completing the reintroduction phase, you’ll have a better handle on which foods to avoid, which foods you can tolerate in small portions, and which foods you can eat freely. 

With a loosened diet, you’ll find it much easier to navigate menus and potlucks so you can relax and enjoy yourself.

How to reintroduce FODMAPs: a 7-step guide

infographic with 7 steps to reintroducing fodmaps

During the reintroduction phase, you’ll continue following the low FODMAP diet to keep your symptoms controlled.  This helps you to more easily determine if the FODMAP you’re testing is the true trigger behind any symptoms that arise.

Even if you “pass” or tolerate a FODMAP group, do not add it back into your diet until you have completed all the FODMAP challenges. 

1. Be open minded

I’ve seen a lot of patients restrict food due to faulty assumptions of intolerance.  This had the effect of limiting their food options, and often affected elements of their social life like eating out and travelling.

Sometimes, people who have negative expectations about a specific food challenge experience worse symptoms (this is the nocebo effect). 

If you don’t have strong evidence that a particular food is a trigger for your IBS symptoms, be open to the possibility that your assumption about it is wrong so you can uncover the truth of your intolerance.

2. Pick a challenge food

The challenge food is a food that is high in the FODMAP group you intend to test your tolerance to.  It shouldn’t contain significant amounts of other FODMAP groups so you know precisely which FODMAP you’re reacting to.  You only need to pick one food from each group to test your tolerance.

Monash University provides examples of challenge foods that are ideal for each FODMAP group (at the time of writing):

  • Lactose – cow’s milk, plain yogurt
  • Fructose – honey, mango, orange juice
  • Polyols (mannitol) – celery, mushrooms
  • Polyols (sorbitol) – apricot, yellow peach
  • GOS – canned green peas, almonds
  • Fructan (onion) – white or yellow onion
  • Fructan (garlic) – garlic
  • Fructan (grains) – white wheat bread, wheat pasta
  • Fructan (fruits and vegetables) – Raisins, Brussels sprouts

One potential problem with some lists of suggested challenge foods that are floating around the internet is that they may be outdated.

An unexpected (and unfortunate) example is Monash’s app. For instance, the app suggests testing GOS at a red light serve using 1/2 cup of green peas. Unfortunately, 1/2 cup green peas is also a red light serve of fructans. This might leave one wondering if their symptoms are the result of the GOS, the fructans, or the combination of both.

Why did Monash suggest certain challenge foods that contain more than one FODMAP when they advise against doing this?  My guess is they didn’t update their suggested challenge food lists when they re-tested foods for their food guide. Thankfully, Monash says they’re working on revising the reintroduction protocols.

There is no set order for reintroducing FODMAPs.  One suggestion is to start with FODMAPs you suspect you’ll tolerate well in order to build up your confidence in the reintroduction process.  For instance, if you’re confident you tolerate lactose, try reintroducing milk as your first FODMAP challenge.

Remember that you won’t be adding FODMAPs you tolerate back into your diet until the entire reintroduction phase is complete.

3. Choose a reintroduction schedule

A reintroduction schedule lays out when to test a particular challenge food.  There are two popular schedules:

1. 3 consecutive days + 2-3 day washout period

The most common reintroduction schedule involves eating the challenge food in progressively larger quantities over 3 consecutive days. 

You then followed take a 2-3 day break from challenges to allow any symptoms to settle before challenging the next FODMAP group.

2. Alternate days for 5 days + 2-3 day washout period

The alternate day schedule involves eating the challenge food on alternate days, for example – Monday, Wednesday and Friday, followed by a 2-3 day washout period.  This schedule is useful for people whose constipation is not well controlled, or for those with anxiety about reintroducing FODMAPs.

If you feel you need a longer washout period in order for symptoms to resolve, then take as long as you need.

Avoid scheduling your food challenges when you have other events that may muddle your results.

For instance, if you have a job interview on day 2 of a FODMAP challenge, re-adjust your reintroduction schedule to finish before the interview or begin after the interview.  This will help prevent the interview stress from affecting your symptoms and clouding your perception of your results.

4. Know your challenge portion

Challenge portions are the amount of the challenge food for a particular FODMAP group that you eat over the course of the 3-day reintroduction.  The portion size gradually increases as you progress through the 3 days so you’re able to determine the amounts of a FODMAP group that you tolerate (ie. your personal tolerance threshold).

Frustratingly, these challenge portions seem to vary in quantity depending on the source.  For instance, the challenge portions recommended in the Monash FODMAP app are different compared to those suggested elsewhere by Monash.  Monash states that “the foods and doses suggested in the reintroduction setting of the app are a guide, not a rule book” (Y).

When I contacted Monash, the Monash FODMAP Team instructed me to stick with the challenge portion protocol they teach dietitians, which is described in this article. It does not align with the challenge portions in their app.  They encourage dietitians to use their judgment and work with their patients to determine appropriate challenge portions.

They also confirmed that they’re working on updating the reintroduction guidance in the app.

So, what are the recommended challenge portions?

  1. Day 1 – an amber light serving size
  2. Day 2 – a smaller red light serving size (eg. the first serving size listed in the app that has a red light)
  3. Day 3- a larger red light serving size (eg. another serving size of your choice that is a bit bigger or perhaps closer to the portion you’d normally eat).

You’ll see that there are times when it may be impractical to eat the red light serving size, or the red light serve is much larger than you’d normally eat. 

For example, the amber serve for blackberries (high in sorbitol) is 1 medium blackberry (7 grams), whereas the red serve is 2/3 cup (160 grams).  Would you ever eat 2/3 cups of blackberries?  Probably not on a regular basis, right? 

In this situation, I’d advise the following:

  1. Day 1 – 1 medium blackberry
  2. Day 2 – 4 medium blackberries
  3. Day 3 – 10 medium blackberries or a portion size my client would typically eat

People who are anxious about potentially developing symptoms during the reintroduction phase can choose smaller challenge portions.

Calendar containing a sample fodmap reintroduction schedule

5. Prepare and eat the challenge food

Here are some dos and don’ts when it comes to eating your challenge food.

Dos:

  • Do: Consume the challenge food alone or alongside other well-tolerated low FODMAP foods. 
  • Do: Eat the entire challenge portion for that day in one sitting. 
  • Do: Eat the challenge food in the morning sometime before lunch if possible to make evaluating your symptoms easier.
  • Do: Eat the food cooked or raw.

Don’ts:

  • Don’t: Use the challenge food (eg. garlic) as an ingredient in a dish that makes multiple servings (eg. pasta sauce) because then you end up eating a much smaller portion than the recommended challenge portion.
  • Don’t: Eat the challenge food if you expect the day to be quite stressful.
  • Don’t: Eat the challenge food as part of a really fatty or spicy meal as these are common triggers for IBS symptoms.

Examples of how to eat challenge foods:

  • Testing garlic (fructans) on day 1?  Add 1/4 clove of garlic to an omelet at breakfast.
  • Testing lactose on day 2?  Drink 1/2 cup of regular cow’s milk as part of a low FODMAP snack in the morning.
  • Testing fructose on day 3?  Add 1 Tbsp of honey to lactose-free yogurt with blueberries for breakfast or morning snack.
  • Testing wheat (fructans) on day 1?  Make 1.5 slices of wheat toast for breakfast.
  • Testing mannitol (polyols) on day 2?  Eat 2 stalks of celery with a bit of peanut butter for morning snack.  (If you’d never eat 2 stalks of celery, aim for 1 stalk of celery on day 2 and 1.5 stalks of celery on day 3).

6. Keep a symptom journal

On each day of your reintroduction schedule, document which challenge food you tested, the portion size, the time you ate it, any symptoms you developed and the time they appeared.  You will also record the intensity of the symptoms as none or mild, moderate, or severe.

7. Interpret your results

People often talk about “passing” and “failing” FODMAP challenges.  Generally speaking, passing suggests you tolerate a FODMAP group, while failing suggests you don’t.

As your challenge food portion increases over 3 days, it’s possible that symptoms will appear.  It’s your job to determine whether the symptoms are mild, moderate or severe.

If you challenge a FODMAP group and experience no or mild symptoms by the end of the 3 days, we could call that a pass.  Should you experience moderate to severe symptoms beginning on day 2 or 3, we’d typically call that a fail.

If you fail a FODMAP challenge, you have some options for handling this: 

  1. You can re-attempt the challenge in smaller quantities once symptoms subside;
  2. You can try challenging it again (possibly in smaller quantities) after you’ve completed your remaining FODMAP challenges;
  3. You can even put off testing that FODMAP for 6 months and then try it again.

Passing a FODMAP group means you can likely tolerate other foods from that group in moderate and high FODMAP portions.  You’ll be able to add foods from this group back into your diet in the third phase of the diet.

Failing means you should stick with low FODMAP serving sizes of foods from that FODMAP group.  For example, if you fail fructans from grains, you’ll want to limit wheat-based grain foods like bread, pasta and crackers to only the low FODMAP serving sizes. 

If you pass fructans in onions and garlic, then you can eat these items in moderate and high FODMAP serving sizes.

Bottom line

Reintroducing FODMAPs is an essential part of the low FODMAP journey but it can be complicated. If you’d like some guidance during this phase, book a discovery call with yours truly to see how I can help you manage your IBS.

xoAndrea, RD

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