Reintroducing FODMAPs: Everything You Need to Know

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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.

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.

The ultimate purpose of identifying your FODMAP triggers is to allow you to add FODMAPs that you tolerate back into your diet, thereby reducing dietary restrictions for better health and quality of life.

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 anywhere from 8-16 weeks depending on your schedule. Each FODMAP group takes roughly 5 days: 3 challenge days plus a 2-day washout period – more about this later.

As you’ll recall, there are 4 main FODMAP groups: Oligosaccharides (fructans and GOS), Disaccharides (lactose), Monosaccharides (fructose), and Polyols. Oligosaccharides are broken down into fructans and GOS, and polyols are broken down into mannitol and sorbitol.

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

So instead of fructans taking 5-ish days, they take about 3 weeks (5 days x 4 fructans) 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 are 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 clear idea of which fructan-rich 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. For instance, if the results of your fructose challenge are questionable, you’ll want to re-do fructose.

Also, I always suggest people put their reintroductions on hold during vacations, social events (eg. weddings), and stressful times like moving house.

Additionally, if your usual diet includes foods that are high in two FODMAPs, such as apples and pears (fructose + sorbitol) or beans/legumes (GOS + fructans), you may want to add these to your reintroduction phase.

When to Start Reintroducing FODMAPs

As soon as you are satisfied with your symptom control, you can start the reintroduction phase. 

To put that in perspective, remember that the low FODMAP diet improves IBS symptoms but rarely eliminates them because IBS symptoms are influenced by other factors such as faulty communication in your gut-brain axis, stress and anxiety, sleep quality, exercise, and the gut microbiome.

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!

What to Expect During 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 2-day washout period you take between FODMAP challenges. 

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

How to Reintroduce FODMAPs: A 7-step Guide

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 called 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 about your intolerance.

2. 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 take a 2-3 day break (called a washout period) from challenges to allow these FODMAPs to exit your digestive tract and let symptoms 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.

3. 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 re-tested a number of foods recently (May 2025) and updated their suggested reintroduction foods. These are examples of challenge foods that are ideal for each FODMAP group (at the time of writing):

• Lactose – cow’s milk or plain yogurt
• Fructose – mango or asparagus
• Polyols (mannitol) – celery or portobello mushrooms or sauerkraut
• Polyols (sorbitol) – cherries or yellow peach
• GOS – silken tofu or pinto beans
• Fructan (onion) – onion
• Fructan (garlic) – garlic
• Fructan (grains) – wheat pasta or couscous
• Fructan (fruits and vegetables) – Ripe banana or Leeks (white bulb)
• Fructose + sorbitol – apple or pear
• Fructan + GOS – canned chickpeas or cashews or frozen peas

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.

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”.

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
3. Day 3 – a larger red light serving size

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 3? 
  • Eat 2 stalks of celery with a bit of peanut butter for morning snack. 

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.

If you develop symptoms, reflect on what you did and ate that day, and make note of any unusual food (eg. alcohol) or possible source of stress (a meeting with your boss). It’s possible these other factors may have contributed to your symptoms, especially if your symptom response to the challenge food seems a bit strange. For example, if you have moderate symptoms on day 1 but mild symptoms on day 2 and 3 as the challenge food portion increases, this may suggest something else triggered your symptoms on day 1.

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. Re-attempt the challenge in smaller quantities once symptoms subside;
2. Challenge it again after you’ve completed your remaining FODMAP challenges;
3. Challenge it 6 months down the road to see if your body’s tolerance has changed.

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 once all your FODMAP reintroductions are complete and you move into the personalization phase.

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/barley/rye-based foods (bread, pasta, crackers, etc) 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