Using a FODMAP diet to optimize gut health

Have you ever heard of a FODMAP diet? It’s a relatively obscure diet for most people until they’re diagnosed with irritable bowel syndrome(IBS).

Subsequently, for those with IBS, a FODMAP diet is life changing. On the other hand, a FODMAP diet may provide benefits to others, even for those who don’t meet the qualifications of IBS

FODMAPs are often an issue for people who experience gas, bloating, stomach pain, diarrhea, & constipation. When someone experiences these symptoms on a weekly basis for at least 3 months and meet other criteria, they are diagnosed with IBS. For further information, check out the Rome IV criteria for IBS diagnosis here.

But what are FODMAPS? Furthermore, what is it about FODMAPs that can give us these symptoms? Finally, how do we properly implement a FODMAP diet to help personalize our diet?

Well, you’re about to find out!

What are FODMAPS?

FODMAP is an acronym for Fermentable Oligosaccharides, Disaccharides, Monsaccharides, And Polyols. These are all short chain carbohydrates found in common foods that we don’t absorb well in the small intestine. As a result, when they get into the colon, they can cause gas, bloating, diarrhea, and constipation.

The first thing you should notice is that FODMAPs aren’t one thing. This is important because each individual may have a problem with some FODMAPs while others are fine. You may have problems with F’s and O’s, but M’s, A’s, and P’s are perfectly fine.

Another important thing to consider is that it may not just be the FODMAPs in a particular food that are problematic. It may be a combination of nutritional factors that includes FODMAPs. Therefore, some F’s may be fine while others are not because they don’t contain the other component.

These are important factors to take into account because many people just blindly eliminate FODMAPs from their diet indefinitely. The purpose of a FODMAP diet is to develop a personalized diet that reduces exposure to foods that cause symptoms for you, not completely eliminate them from your diet.

As the name suggests, FODMAPs can be beneficial to your microbiome as they are fermentable. We just don’t want to eat the ones that cause GI problems, which varies from person to person.

How do FODMAPS cause symptoms?

As you can imagine, one of the primary ways that FODMAPs cause symptoms is via their fermentation by microbes in our gut. However, this isn’t the only way that FODMAPs can cause symptoms in people.

This handy little flowchart shows how FODMAPs can produce myriad symptoms of gas, bloating, diarrhea, and constipation in some people.

There are 3 primary ways that FODMAPs cause symptoms in the gut. Firstly, FODMAPs can have an osmotic effect. This means they pull water into the intestine which affects how bloated we feel and our bowel habits. Typically, when this happens in the colon, it leads to diarrhea.

Secondly, gases produced by bacteria such as methane(CH4), hydrogen(H2), and carbon dioxide(CO2) cause us to feel gassy and bloated. They also cause downstream effects to both the microbiome and gut function.

For example, microbes called methanogens use carbon dioxide(CO2) and hydrogen(H2) to produce methane(CH4). Higher levels of CO2 and H2, therefore, will increase the presence of methanogens and increase methane production.

In the gut, methane and other gases known as gasotransmitters can affect how quickly food passes through the colon. Specifically, methane slows down motility and can, therefore, cause constipation in some people.

Finally, FODMAPs cause symptoms through the production of short chain fatty acids(SCFAs). SCFAs are generally beneficial products of fermentation by the microbiome. But as always, balance is key.

The most prevalent SCFAs are butyrate, propionate, and actetate, though there are others. Like gases, SCFAs can alter gut function. Furthermore, SCFAs also have osmotic effects, pulling water into the gut.

One final way that SCFAs impact the environment in the colon is by changing the pH. As their name suggests, short chain fatty acids increase acidity and decrease pH. An imbalance of SCFAs alters pH which changes the microbiome due to the changing environmental conditions.

Who is a FODMAP Diet for?

In general, a FODMAP diet may benefit people with many different gut issues. While IBS is the primary reason people do a FODMAP diet, papers shows a FODMAP diet benefits Crohn’s disease, IBD, and celiac disease.

Ultimately, anyone with IBS-like symptoms may see some benefit from a FODMAP diet. In the above referenced studies, those with the specific diseases also experienced IBS-like symptoms.

So if you experience IBS-like symptoms regularly, but not enough to meet the critiera for IBS, you may want to take a look and see if maybe you’re loading on some foods high in FODMAPs. You likely won’t have to follow the standard protocol for those with IBS or other functional GI disorders, just identify problematic foods and try reducing them for a period.

So, how does one do a proper FODMAP diet?

How to implement a proper FODMAP diet

The first step in a FODMAP diet is knowing which foods are high and low in FODMAPs. You can check out a comprehensive list at

Now, you may have noticed that we’ve used the term FODMAP diet throughout this blog rather than the term low FODMAP. The reason for this small adjustment is pretty important. Using the term low FODMAP implies that you should restrict all FODMAPs forever.

Many take the plunge into a FODMAP diet thinking they have to restrict all FODMAPs all the time. But there are 3 phases to the diet, and the goal is to personalize your diet to identify the specific FODMAPs you are sensitive to and limit them. Not remove all FODMAPs from your diet forever.

Phase 1-Low FODMAP diet

In this phase, you focus your diet around lower FODMAP foods while restricting foods high in FODMAPs. This stage should last 2-6 weeks depending on your symptoms. Ideally, you will develop a control diet that minimizes symptoms so that you can move on to stage phase 2.

Phase 2-Reintroduction

In phase 2, you begin reintroducing higher FODMAP foods one at a time. You should only reintroduce 1 new food every 3 days so you can get a handle on how you respond to that food. Remember, it takes 24 hours or more for food to reach your colon, so you may not experience symptoms right away.

Start with a small portion of a food and increase it over each of the 3 days. If you get away symptom-free, that food should be ok to add back into your diet. If you experience symptoms over the 3 day trial period, remove that food and move on to the next one.

Keep in mind the amount you eat may be just as important as the food itself. If you don’t experience symptoms until day 4 after reintroduction, you may tolerate that food in lower quantities.

Generally speaking, it’s best to have 3 separate buckets for the foods you try in the reintroduction phase: Foods you don’t tolerate at all, foods that you tolerate in small amounts, and foods you can eat freely.

Phase 3-FODMAP personalization

In phase 3, you should have a personalized list of foods that cause symptoms for you. Some of these foods you’ll have to avoid altogether, some you’ll have to limit, and some you can eat freely without concern.

As the name suggests, each person will have their own unique FODMAP diet after this phase. For some this may be a low FODMAP diet, but for others it may simply be a diet that restricts a small number of specific FODMAPs.

At the beginning of this process, during the elimination phase, many see such dramatic improvements that they simply just continue to restrict FODMAPs altogether. While at the time this may seem like a good idea, people often end up with a fairly restricted list of foods further down the road.

This is an even bigger problem if you restrict other food components such as histamine or oxalate. Therefore, make sure you carry this entire process to completion so that you have a personalized diet that makes you feel good and gives you a lot of options at your disposal.


A FODMAP diet is very effective for reducing symptoms in those with IBS. However, people with other gut disorders as well as people with no gut problems often experience IBS-like symptoms such as:

  • Gas
  • Bloating
  • Stomach discomfort
  • Diarrhea
  • Constipation

If these symptoms are negatively impacting your quality of life, a FODMAP diet may help you discover foods that are causing these symptoms. Those with IBS or severe symptoms should go through the entire 3 phase FODMAP diet to get their symptoms under control and develop a personalized diet.

If you simply get gassy or bloated from time to time, take a look at the high FODMAP food list and see if you may be eating a food that’s not right for you, or consuming too much it.

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