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The Low FODMAP Diet: What You Need to Know

The low FODMAP diet is wildly popular in gut health circles these days, mainly as an intervention for irritable bowel syndrome, but unfortunately it’s often misunderstood.

This blog will explain what’s involved in the low FODMAP diet, how effective it is, and who it’s intended for. Stick around until the end and you’ll find a bundle of resources that should make following the diet a bit easier.

While the low FODMAP diet is incredibly helpful, it is also complicated and not suited to everyone.  The following blog is intended as education and not personal health advice.  If you’re curious to know whether the low FODMAP diet is right for you, connect with a Monash FODMAP trained dietitian (like yours truly 😊) to explore the possibility.

What is the Low FODMAP Diet?

The low FODMAP diet is an elimination diet that involves temporarily reducing foods rich in fermentable carbohydrates that contribute to bloating, abdominal pain and diarrhea in people with IBS.  Once symptoms are under control, high FODMAP foods are systematically reintroduced back into the diet as a means of identifying which foods trigger digestive symptoms.

FODMAPs are found in a wide array of foods that contain carbohydrates, such as fruits, vegetables, nuts and seeds, grains and grain products, legumes, and dairy.  They are not found in meat, poultry, eggs or fish, nor in fats like butter and oils.

FODMAP Groups and Food Sources

The term ‘FODMAP’ is an acronym that stands for the main groups of fermentable carbs that can cause such unpleasantness in IBS.


The carbohydrates in the following groups are poorly digested and then fermented by gut bacteria.  Fermentation is a process whereby bacteria in the large intestine break down FODMAPs and release gas as a by-product.


There are two FODMAP sub-categories in this group:

1) Fructans

2) Galacto-oligosaccharides (often referred to as GOS). 

Common sources of fructans: Garlic, onion, wheat and wheat products (eg. bread, pasta, crackers), barley, and rye.

Fructans are also found in some fruits and vegetables, such as Brussels sprouts, dried fruit, and grapefruit. 

Common sources of GOS: Beans, legumes, soy and nuts like cashews, pistachios and almonds.


The disaccharide at issue here is lactose.

Common sources of lactose: Dairy, such as milk, yogurt, ice cream, cottage cheese, and sour cream.  Hard cheeses, like cheddar, mozzarella and parmesan, contain only very small amounts of lactose.


Fructose, in excess of glucose, is the monosaccharide to which this group refers.  When a food contains more fructose than glucose, the body has trouble absorbing the fructose so it remains in the intestine and triggers symptoms. 

Common sources of fructose: Fruits and vegetables, such as grapes, mango, asparagus, bell peppers, sugar snap peas, etc.



Polyols are naturally-occurring sugar alcohols, such as mannitol and sorbitol.

Common sources of polyols: Fruits and vegetables, such as blackberries, stone fruits, apples, pears, mushrooms, celery, corn, etc. Also, low-calorie and/or low-sugar candies, protein bars, etc.

list of fodmap groups with images of their food sources

The 3 Phases of the Low FODMAP Diet

The low FODMAP diet isn’t a forever diet. Instead, it’s an elimination diet with 3 phases:

  1. Phase 1 – The Elimination Phase. During the elimination phase, people cut out foods containing moderate and high amounts of FODMAPs for about 3-6 weeks, until symptoms are adequately improved.
  2. Phase 2 – The Reintroduction Phase. In phase 2, people continue a low FODMAP diet to maintain symptom control but begin reintroducing high FODMAP foods one group at a time to determine which group stimulates symptoms.
  3. Phase 3 – The Personalization Phase. In this phase, people slowly add tolerated foods back into their diet.  They can begin to eat moderate and high FODMAP foods from the FODMAP groups they tolerate.  At the same time, they stick with only low FODMAP serving sizes of FODMAPs they didn’t tolerate during the reintroduction phase.

Monash University and the Low FODMAP Diet

Researchers at Monash University (in Australia) first conceived of and then developed the low FODMAP diet for IBS symptom management. Monash continues to be the leader in research, food testing, education, and knowledge translation involving the low FODMAP diet.

Monash scientists have lab tested many foods and products to determine their FODMAP content.  They use a traffic light system to categorize these foods as low FODMAP (green), moderate FODMAP (yellow) and high FODMAP (red). 

Many foods categorized as high FODMAP have smaller low FODMAP serving sizes that people can eat during the elimination phase of the diet.  This helps to considerably expand food options on an otherwise pretty restrictive diet.

Not surprisingly, the Monash FODMAP app is the most comprehensive and informative resource for “food lists” pertaining to the low FODMAP diet.  Low FODMAP food lists people find online or receive from health care providers are often out of date or just plain incorrect.  The Monash app is the best source for FODMAP food lists.

How Do FODMAPs Trigger IBS Symptoms?

FODMAPs are poorly digested and absorbed in the human body.  People with IBS have visceral hypersensitivity, which loosely means that they have an overly sensitive digestive system.  As a result, the effects of FODMAPs in the body are more keenly felt and interpreted as pain by IBS sufferers.

Let’s look at the two major ways FODMAPs trigger IBS symptoms.

1. Fermentation

When the poorly digested FODMAPs reach the large intestine, the bacteria there break them down and release gas in a process called fermentation.   As gas accumulates in the large intestine, it leads to flatulence, bloating, and distension of the colon wall. 

In people with IBS (who also have visceral hypersensitivity), the distension of the colon wall leads to pain.

Fructans, such as garlic and onion, and GOS, such as beans, are especially prone to fermentation.

2. Excess Water in the Gut

Some FODMAPs, particularly fructose and polyols, draw excess water into the intestine in a process called the “osmotic effect“. 

This influx of excess water stretches the intestinal wall and moves the contents of the gut along faster (ie. increased gut motility).  When gut motility speeds up, the potential for abdominal discomfort and diarrhea is greater.

Lactose is a Unique FODMAP

Lactose is unique among the FODMAPs in that, unlike the other FODMAPs, it has its own dedicated enzyme designed to break it down and allow our bodies to absorb it.  This specialized enzyme is called lactase.

People vary in their lactase enzyme levels.  For some, lactase declines with age, while for others lactase remains stable and allows for dairy consumption late into life.   We describe the condition of not producing enough lactase to comfortably eat dairy foods as lactose intolerance.

When lactose isn’t sufficiently broken down, the osmotic effect kicks in and the end result is gas, abdominal pain and diarrhea.

Other Ways FODMAPs Trigger Symptoms

Other ways FODMAPs may affect symptoms include their effects on intestinal bacteria and immune system activation. These possible mechanisms of influence are complex and less well understood so we won’t dive into them today.

What’s Your FODMAP Tolerance? The Bucket Analogy.

The bucket analogy is often used to explain variations in FODMAP tolerance levels, and can be applied to other food intolerances too. 

Imagine your tolerance to FODMAPs as a bucket.  You can add FODMAPs to your bucket, but eventually the bucket overflows, and it’s at this point that you start to feel symptoms. 

Everyone has a different bucket size, which is to say that everyone has different levels of tolerance for FODMAPs.   For some people, the bucket is small and they experience symptoms after eating moderate amounts of FODMAPs. For others, the bucket is larger and the amount of FODMAPs they can tolerate before symptoms appear is more generous.

Additionally, people differ in which FODMAPs take up more real estate in their buckets.  For example, fructans take up more space in the buckets of people who are particularly sensitive to garlic, onion and wheat.

Bucket size (ie. tolerance level) can also be affected by negative emotions that decrease pain thresholds in the gut. Because of this reduction in pain thresholds, stress and anxiety can cause a person to feel digestive symptoms at usual FODMAP intakes, or even with foods they normally tolerate. 

How Effective is the Low FODMAP Diet?

Quite effective. In fact, the low FODMAP diet improves digestive symptoms in roughly 70% of people.  That’s a lot of people!

Short-Term Symptom Improvement

IBS symptoms that improve in severity and frequency on the low FODMAP diet include:

  • bloating
  • flatulence
  • abdominal pain
  • diarrhea  

Among studies evaluating the diet, one found that peoples’ symptoms improved after only 7 days.

Constipation remains the only symptom that isn’t significantly improved on the low FODMAP diet.  Since more studies investigate IBS-D than IBS-C, and most studies tend to have more IBS-D participants than IBS-C participants, it’s possible we just don’t have enough research on how the low FODMAP diet affects constipation.

Regardless, poorly controlled constipation can result in symptoms similar to FODMAP intolerance, such as excess gas, bloating and abdominal pain. For this reason, it’s wise for people to manage their constipation before starting the low FODMAP diet in case improved bowel habits alleviate digestive symptoms. 

Long-Term Symptom Improvement

A few studies have looked at the long-term effects of the low FODMAP diet on symptom management, and overall the findings are positive.  

Most people sustain satisfactory symptom control after adding FODMAPs back into their diet.  The microbiome appears to bounce back too, meaning that bacteria whose numbers went down during the elimination and reintroduction phases of the diet rebounded once a person begins their personalized diet.

More research is needed on the long term effects of the diet, as it’s difficult to make definitive statements based on only a few studies.  That being said, the existing literature is promising!

Pros and Cons of the Low FODMAP Diet

The low FODMAP diet can be incredibly helpful, but it’s not without its drawbacks.

Pros of the Low FODMAP Diet

  1. Of all the dietary interventions for IBS, the low FODMAP diet has the most research and best results.
  2. As described above, the low FODMAP diet improves symptoms that cause particular distress in IBS: bloating, gas, and abdominal pain.
  3. The low FODMAP diet improves diarrhea.
  4. People report improved quality of life on the low FODMAP diet.
  5. People can identify their food triggers.  This in turn enables people to be more precise with their food restrictions and to include more foods they may have previously restricted in error (which I’ve seen many times!).
  6. The low FODMAP diet gives people a sense of control over their diet and symptoms.
  7. As an elimination trial, the low FODMAP diet is short-term so people don’t have to follow the tight restrictions forever.
  8. Scientists re-test foods often to ensure the data on FODMAP content is up to date.
  9. There are more resources and products to help people navigate the diet than ever before (see Resources section below).

Cons of the Low FODMAP Diet

  1. The number of food restrictions makes it more challenging for people to eat out and travel.
  2. The low FODMAP diet is complicated, so it’s easy for people to follow it incorrectly.  This can lead to poor results or misinterpretation of symptom triggers.
  3. It likely won’t significantly improve constipation in IBS-C.  Strategies specific to constipation are needed as well.
  4. It may impair a person’s nutrition (though the research on this is mixed), reduce fibre intake, and temporarily alter the gut microbiome.  More research is needed.
  5. Groceries are more expensive (eg. gluten-free products).
  6. Elimination diets can put people at increased risk of developing disordered eating.
list of pros and cons of the low fodmap diet

Who is the Low FODMAP Diet for?

Scientists developed the low FODMAP diet for the treatment of IBS symptoms, but the diet isn’t necessarily suitable for all adults with IBS.

Because the low FODMAP diet is complicated, people with IBS who tend to adapt fairly well to the low FODMAP diet include those who:

  • Can carve out time in their lives to devote to the 3 phases of the diet.
  • Possess decent cooking skills.
  • Have solid meal planning and organization skills.
  • Are resourceful in seeking out answers to questions that inevitably arise.
  • Have control over the food they buy and eat.
  • Have support from loved ones, especially people they live with.

People who may struggle to follow and stick with the low FODMAP diet include those who:

  • Have a lot going on in their lives and feel it would be a struggle to find the time and energy to embark on a complex 3-phase elimination diet.
  • Travel a lot for work, or eat out often without the capacity to cut back on this. 

People who should consider forgoing the low FODMAP diet and trying alternative diet and lifestyle therapies include those who:

  • Strongly suspect that stress or anxiety is the primary trigger for symptoms.
  • Have an active eating disorder, or a history of an eating disorder. The diet increases the chances of relapse.

Variations of the Low FODMAP Diet

The FODMAP gentle diet is the main variation that people are likely to come across. 

While people who follow a strict low FODMAP diet avoid foods with moderate and high amounts of FODMAPs, people following the FODMAP gentle diet avoid only foods that are very high in FODMAPs.

Consequently, the FODMAP gentle diet has a much shorter list of dietary restrictions.

Unfortunately, there is no research on the FODMAP gentle diet so we can’t say with any certainty that it’s effective at alleviating IBS symptoms.  Anecdotally, Monash FODMAP trained dietitians often report that it’s helpful in certain people, such as those with a very high FODMAP diet or people with mild symptoms.

Another “variation” of the low FODMAP diet involves a Monash FODMAP trained dietitian cherry picking only FODMAP groups that are highly suspected of being someone’s triggers after careful assessment of the client’s diet and symptom patterns.

This tailored approach is beneficial for: 1) people who would find the low FODMAP diet overwhelming, 2) people with a history of disordered eating, 3) people with other dietary restrictions, 4) people at risk of malnutrition.

Essential Low FODMAP Resources

I’ve written a few blogs on navigating the low FODMAP diet that you’ll find helpful so hop over and check those out:

Reliable IBS Information

There’s a lot of misinformation online about IBS, so here are some trusted resources for further reading:

Dietitian-Run Low FODMAP Blogs

Low FODMAP Recipes


These apps make life on the LFD a bit easier. In my professional opinion, the Monash FODMAP app is an absolute must if you’re going on the low FODMAP diet.

Monash FODMAP App – This app provides a comprehensive and regularly updated list of foods and products that have been lab-tested for FODMAP content.  It also provides serving size information for high FODMAP foods that can be consumed in low FODMAP portions.  In addition, you’ll find a food & symptom journal, recipes and instructions on reintroducing FODMAPs (phase 2 of the diet).

FODMAP Friendly App – Although it is less comprehensive compared to the Monash app, the FODMAP Friendly app is another app that categorizes lab-tested foods according to FODMAP content. 

Spoonful App –  This app sans barcodes on food products to tell you the likelihood of something being low or high FODMAP based on the ingredients list.

Low FODMAP Certification

There are two programs that certify food products as low FODMAP.  With both of these programs, the food products are lab-tested for FODMAP content.   Keep your eye peeled for these two symbols on food packaging:

  1. Monash University Low FODMAP Certified   
  2. FODMAP Friendly Certified 
Two low fodmap certification symbols by Monash and Fodmap Friendly

Low FODMAP Meal Delivery Services

If you’re keen to try the low FODMAP diet but cooking is a barrier, look into low FODMAP meal delivery services:

Check out my review of Gut Feelings meal delivery service HERE.

7 low fodmap meals on a countertop

I hope this post gave you some much-needed clarity on the low FODMAP diet.

If you feel you need professional guidance navigating this effective yet complex diet, seek out a Monash FODMAP-trained dietitian or book a free 15-minute discovery call (if you live in Ontario) with me and we’ll discuss how I can help.

xoAndrea, RD

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