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Introduction

Congratulations on making it through the Low FODMAP Elimination Phase! The next phase of the diet is the Reintroduction Phase. If you’re just getting started with Low FODMAP, go back and read my introduction to FODMAPs and the Low FODMAP diet first.

Now it’s the exciting time to reintroduce some of those favorite high FODMAP foods you’ve been missing back into your diet. The goal of the reintroduction phase is to learn which FODMAPs trigger your symptoms and in what quantities.

During this phase, you will learn about your tolerance to a particular FODMAP group (Fructose, Lactose, Fructans, etc.), rather than a single, specific food. However, you will be using specific foods to test your tolerance to those groups. For example, if you find you are able to eat honey without symptoms, this means you should be able to safely tolerate larger portions of other high fructose foods such as mangos or sugar snap peas.

If you use the Fig app to find low FODMAP groceries, make sure to update your settings to match your stage of reintroduction.

Why reintroduce FODMAPs?

Many people are reluctant to reintroduce foods, especially if they’re feeling much better without symptoms. However, it’s important for your health to do this reintroduction phase.

Everyone’s tolerance to FODMAPs is unique and the only way to find your own threshold is through systematically testing each group. Having this knowledge will give you a sense of control and empowerment because you finally understand which FODMAPs have been causing your symptoms – and you can make future food choices accordingly. For instance, if you learn that fructans in wheat cause you stomach pain but decide to eat that piece of cake anyway, then at least you know what caused it and are no longer in the dark!

Although there aren’t enough studies to understand the long-term health effects of staying in the Low FODMAP Elimination Phase, we do know that this diet alters the gut microbiome which may have unknown health consequences. Specifically, a low FODMAP diet restricts fructans and galactooligosaccharides (GOS) which have beneficial prebiotic health effects on the microbiome. Similarly, staying on a restricted diet can make it difficult to meet all of your nutritional needs.

Finally, the FODMAP Elimination Phase can be socially isolating, since so many of our special occasions revolve around food. Ultimately, it’s best for your overall health and your social life to enjoy as varied a diet as possible while keeping symptoms under control!

Reintroduction Basic Guidelines

During this phase, you’ll methodically reintroduce high FODMAP foods back to your diet, one FODMAP group at a time, to understand which ones cause your symptoms. This is called “challenging” a FODMAP group. To challenge each FODMAP group, you’ll follow these steps:

Step 1

Pick a FODMAP group like lactose or fructose to challenge. The order doesn’t matter so you can start with a favorite group you’ve been missing or one you think you’re likely to tolerate to give you momentum to continue.

Step 2

Pick a test food from that FODMAP group. Use the Monash App to determine your test foods or follow your dietitian’s guidelines. Make sure to pick a test food that only has ONE type of FODMAP, not multiple. For example, larger servings of button mushrooms contain both fructans and mannitol, so this would not be a good test food.

Step 3

You’ll test this same food over three consecutive days to see if you have symptoms. On the first day, start with a small portion, slowly increasing the amount consumed on the second and third days. Make sure you test the same food for each of the three challenge days. For example, if you chose milk from the lactose category, test only milk for each of the three days. Stop the challenge at any time if significant symptoms occur. 

Step 4

You can test each FODMAP group over three consecutive days or by taking a rest day between each test day. Fructans and GOS take longer to work through the digestive tract than other FODMAP groups, so it may be best to leave a day in between test days for these foods to allow time for symptoms to arise. As an aside, if you have very slow moving gut transit in general (constipation predominance), waiting a day between each test day for all FODMAP groups may be the best option for you.

Step 5

It’s best to eat the high FODMAP test food with a meal and not by itself to help with absorption and give you a better chance of success. For example, if testing honey, drizzle it on a slice of low FODMAP bread or put the honey in tea alongside a meal rather than just eating honey on its own.

Step 6

After you’ve finished challenging one FODMAP group, rest at least three days before starting the next group. Why? There may be carryover FODMAPs in your system from the largest portion size tested which could interfere with the results of your next challenge. For example, if you just tested a large portion of fructans without symptoms and the next day you start a challenge of sorbitol and get symptoms, it might have been the combination of fructans and sorbitol triggering symptoms rather than the sorbitol on its own.

Step 7

If you pass a FODMAP challenge, that’s great! But don’t add that FODMAP group back into your diet just yet. Keep it out of your diet until all challenges are complete, at which time you’ll slowly add back in the high FODMAP foods you passed. During the final Modified Phase, you’ll learn more about how combining FODMAPs in a day or even in a meal affects your symptoms.

What does failing a FODMAP challenge mean?

Failing a challenge means you experienced a noticeable and significant change in symptoms like an IBS flare up. If you experienced mild bloating or extra gas on any test day, this is ok and can be a normal reaction to FODMAPs, as long as these symptoms are not painful or otherwise life disrupting.

If you failed a challenge, you should avoid eating that FODMAP group in that quantity. For example, if you tolerated ½ cup of milk with no problems but experienced significant symptoms after 1 ½ cups, take note of this because it means you should be ok to include small amounts of milk in your diet once you reach the Modified Phase. For example, this amount may be enjoyed in a small bowl of cereal, in a small coffee, or as part of a recipe with a limited amount of milk. It’s important to know your tolerance to FODMAPs can change over time, so it’s recommended to challenge each group again periodically!

Tracking your progress

Throughout the reintroduction phase, be sure to track which FODMAP groups and foods you are testing, the quantities you tested, what time you tested them, and what, if any, symptoms occurred. It’s also useful to note if the symptoms were mild, moderate, or severe. All of this information is going to be helpful to you later when you’re doing the final Modified Phase.

FODMAPs take some time to get from the mouth to the colon (generally 4-24 hours), so it can be helpful to observe on your tracking sheet how long your reactions take. If you eat a high FODMAP food and five minutes later experience severe symptoms, this is not from the food you just tested. This is a reaction from something you ate earlier. Please note that allergic or other biochemical reactions can occur quickly after eating, such as hives, difficulty breathing, vomiting, and diarrhea, but these are not related to FODMAP reactions.

Sample FODMAP reintroduction schedule

Challenge Day 1

Eat the smallest portion of the challenge food along with your usual low FODMAP diet. If mild or no symptoms occur, move onto the next portion size. If moderate to severe symptoms occur, then stop the challenge. Resume the low FODMAP Elimination Phase until you are symptom free for three days.

Challenge Day 2

Eat the medium portion size of the challenge food along with your usual low FODMAP diet. If mild or no symptoms occur, move onto the next portion size. If moderate to severe symptoms occur, then stop the challenge. Resume the low FODMAP Elimination Phase until you are symptom free for three days.

Challenge Day 3

If at any point moderate or severe symptoms occur, do not push yourself further onto the next day of the challenge. There is no point, and you will only make yourself feel terrible!

FODMAP reintroduction example foods

This is a sample of reintroduction food choices. When possible, it’s always best to work with a dietitian for an individualized and guided challenge structure.

FODMAP Group	Possible Test Food
Excess Fructose	Honey or mango (for honey, start with 1 1/2 teaspoons increasing to 2 tablespoons over the three testing days)
Lactose	Milk or cottage cheese (choose low fat versions if fat is a trigger for your symptoms)
Mannitol	Cauliflower or sweet potato
Sorbitol	Avocado or yellow peach
Galacto-oligosaccharides (GOS)	Almonds or canned butter beans
Fructans	Due to the varied levels of fructans in foods, it’s recommended to test each fructan category separately as noted below. It’s possible to tolerate garlic but not onion and vice versa, so it’s important to test both! Fructans fruit: Grapefruit or dried cranberries Fructans wheat: Wheat bread or couscous Fructans onion: White or red onion or leek bulbs Fructans garlic: Garlic
Fructose/Sorbitol combined	Apples or pears Test combined fructose/sorbitol only if you passed the individual sorbitol and fructose tests.

Success strategies

Try to start the Reintroduction Phase when things are pretty normal in your life and stress levels are low. I wouldn’t recommend going out to eat during the days you are testing, because we never really know what is added to restaurant foods. Avoid starting reintroduction if you’ve also recently started taking any new medications or herbal treatments. I tell my patients it’s like a science experiment: if you change too many things at once, it will be very difficult to tell if it’s a FODMAP reaction or if you are reacting to something else.

Though you’re very unlikely to fail all of the FODMAP challenges, it may indicate a different underlying condition such as SIBO (Small Intestinal Bacterial Overgrowth). It’s more likely that you accidentally consumed other high FODMAP foods. This is why working with a dietitian can be so helpful. 

Finally, I will stress again the importance of the Monash FODMAP app. This app shows which foods are high and low in FODMAPs and at what portion sizes. Once you know your specific FODMAP triggers, you can update your settings in the Fig app to find groceries that match those specific needs.

The information you glean from the FODMAP Reintroduction Phase will give you everything you need to know for moving onto the final phase of the diet, the Modified Phase. The goal of that final phase is to find the sweet spot for you: the place where you can eat the most diverse and healthiest diet while keeping your symptoms under their best control.