All FODMAPs are not created equal

We have our Medical Advisor and Nobel Laureate, Prof Barry Marshall to thank for the idea for this week’s blog. It illustrates the fact that academic gastroenterologists across the globe are working hard to try and improve outcomes for their patients and prompts some ideas for ways to make life easier for people with IBS considering changes in their diet.

Barry sent us a link to a paper published in the latest edition of Clinical Gastroenterology and Hepatology. The research was undertaken at the University of Michigan and the research team included Prof William Chey, a well-respected researcher in the IBS space.

We thought you’d like to hear about it too.

All FODMAPs aren’t created equal

The study "All FODMAPs Aren’t Created Equal: Results of a Randomized Reintroduction Trial in Patients With Irritable Bowel Syndrome" was conducted against the backdrop of the challenges faced by individuals with irritable bowel syndrome (IBS) in sticking to the traditional low FODMAP diet.

Many clinical trials have now demonstrated that the diet is effective in managing IBS symptoms. However, it’s first stage requires the elimination of a wide range of foods containing fermentable carbohydrates (FODMAPs), such as garlic, certain fruits and vegetables, and gluten-based bread. As we know, this restrictive approach can be difficult to implement and sustain, leading the study researchers to ask whether the diet could be tweaked to make it easier.

The researchers sought to identify which individual FODMAPs were most likely to trigger symptoms in IBS patients and to evaluate the likely potential of a simpler dietary approach.

It’s the first step in exploring whether targeting specific FODMAP groups, rather than all of them, could provide similar symptom relief. This bottom-up approach (eliminate 2 FODMAPs first, and if that doesn’t work, add more) could make the diet more practical and less burdensome for patients, than the traditional top-down approach.

The study employed a two-phase methodology to investigate individual FODMAP sensitivities in IBS patients.

Methodolody

Here's an overview of the approach:

1. Participants: The study recruited patients with clinically diagnosed IBS. A total of 45 participants were enrolled between 2018 and 2020.

2. Initial Elimination Phase: Participants underwent a 2-4 week elimination phase, during which they followed a traditional low FODMAP diet. This phase aimed to identify individuals who experienced symptom improvement with FODMAP restriction. The researchers defined an improvement as a 30% reduction in abdominal pain.

3. Blinded Reintroduction Phase: Of the initial group, 25 participants showed symptom improvement and 21 continued to the reintroduction phase. In this 10-week phase, participants were reintroduced to individual FODMAP groups (e.g., lactose, excess fructose, polyol, fructan & GOS) in a blinded and random manner. The researchers used standard samples of the FODMAPs and these were baked into brownies. Each of the five FODMAP groups was reintroduced for seven days (first at a low levels and then higher), with a ‘wash-out’ period of a week in between when the participants returned to a full low FODMAP elimination diet. They returned to this early if they experienced symptoms from the reintroduced FODMAP.

4. Symptom Monitoring: Throughout the study, participants recorded daily symptom severity using a 0-10 numerical rating scale. This data was analyzed using a sophisticated mixed-effects statistical model to assess the impact of specific FODMAPs on symptoms, especially bloating and abdominal pain.

Main Findings

The results indicate that not all FODMAPs equally contribute to symptom generation.

1. Individual Sensitivities: The study found that IBS patients typically react to only a subset of FODMAPs rather than all of them. An average of 2 FODMAPs per person. This suggests that a more targeted dietary approach could be effective.

2. Fructans and GOS as Key Triggers: Fructans (found in onions, garlic, and wheat) and galacto-oligosaccharides (GOS, found in legumes and cruciferous vegetables) were identified as the most common triggers for symptoms like abdominal pain and bloating.

3. Simplified Diets: The findings support the development of a diet that restricts only fructans and GOS, as an alternative to the traditional low FODMAP diet that eliminates all FODMAP groups. This simplified approach may show similar effectiveness in reducing IBS symptoms while being easier to follow.

But hang on a minute…

There are a few caveats. The study has some limitations.

1. The sample size was very small. Just 21 participants made it all the way through the study, meaning we may not be able to generalise from the results. A similar, older study found a different group of FODMAPs was important in triggering symptoms.

2. The researchers used just one type of each FODMAP in the reintroduction testing. For example they used just one length of fructan, but there are many, many types of fructans found in various food groups (e,g., wheat and fruit) and the results may not reflect real world conditions.

3. The researchers focused on just two symptoms, abdominal pain and bloating, both in terms of which participants were included in the reintroduction part of the study and determining whether a FODMAP was a trigger for each individual participant. They did this because these are the symptoms that are typically most troublesome to patients. If you are struggle more with other symptoms, such as urgency or constipation, the study results may be less relevant to you. For example, diarrhoea is most commonly linked to the polyols (mannitol and sorbitol), fructose and lactose.

4. The researchers found that overall IBS symptoms increased over the 10 week reintroduction period indicating perhaps that the week long wash-out period between FODMAP reintroductions wasn’t long enough, or perhaps that the study participants found it harder to adhere to a full low FODMAP elimination diet as the study progressed.

With all that in mind, here are what we consider to be the

Key Takeaways for IBS Patients Considering the Low FODMAP Diet:

1. Personalization is Key: The really good news from this study is that it indicates that it’s likely that not all FODMAPs trigger your symptoms. It could be just 2 FODMAP groups that are troublesome for you. Don’t stay in elimination phase, work through the reintroductions to personalisation. Working with a dietitian can make this easier, but identifying your specific sensitivities will make the diet much more manageable and sustainable. And if you need an easy low FODMAP meal at any stage along the way, Superflora shakes blitzed with a low FODMAP milk and a little fruit (1/3 ripe banana, 5 raspberries or ½ cup of blueberries) is a quick and easy option – or check out our recipe page for 100s of ideas.

1. Focus on Fructans and GOS: If you're overwhelmed by the traditional low FODMAP diet, you could consider starting with a focus on reducing fructans and GOS, as these are the most common triggers (of bloating and abdominal pain at least). However, the researchers in the study rightly pointed out that a large-scale clinical trial is really needed to compare this approach to the standard low FODMAP diet before it can be widely recommended. In the same edition of Clinical Gastroenterology and Hepatology, Prof Chey and colleagues presented the results of a small pilot trial. They found that a simple diet restricting only GOS and fructans led to similar reductions in abdominal pain, bloating, and discomfort compared with the traditional low FODMAP diet, but it was not as effective at improving stool consistency. If you struggle with diarrhoea, it’s likely you’ll need to reduce polyols, fructose, and/or lactose too.

2. Simplified Approach: The "Simplified FODMAP Diet" diet could also be a practical alternative, offering symptom relief without the need for extensive dietary restrictions. We’ve given an outline of this diet below – it was developed by the team at Monash University and takes into account all five FODMAP groups but restricts only commonly consumed very high FODMAP foods. This simplified approach may provide similar symptom relief while being easier to implement and sustain. If you are overwhelmed by the idea of the full FODMAP diet, this could be a good first step. It may well provide some relief for you.

3. Fine Tuning the Reintroduction Phase: Whether you go with the full low FODMAP diet or take a simplified approach, the reintroduction phase is important to allow you to personalise and broaden you diet as much as possible.  A few tweaks may make the process more effective. The study indicates that FODMAP effects seem to accumulate and that you may need longer than a week between reintroductions to let your gut settle down and get a clear picture of which FODMAPs trigger symptoms. If you already have some ideas about your triggers, think about testing those last.

Final Thoughts

The “All FODMAPs Aren’t Created Equal” study allowed the researchers to pinpoint fructans and GOS as the primary triggers for symptoms like abdominal pain and bloating.

It also provided a foundation for exploring the possibility of simplified dietary approaches for IBS management.

For people with IBS considering the low FODMAP diet, this study provides hope for a manageable path to symptom relief. It is likely that an effective, personalised low FODMAP diet excluding a couple of FODMAPs can be determined, or that a simplified low FODMAP approach can offer a balance between effectiveness and practicality.

If you're exploring any of these dietary options, consulting with a dietitian is useful for achieving long-term success.

Key Features of the Monash Simplified Low FODMAP Diet:

Unlike the traditional low FODMAP diet, which requires strict adherence to avoid all high FODMAP foods, the FODMAP-simple diet allows for a more relaxed approach by targeting only the most significant triggers.

This simplified approach can be particularly beneficial for individuals who find the full low FODMAP diet overwhelming or difficult to sustain.

Restricted Foods:

• Grains: Wheat and rye-based products.

• Vegetables: Onion, garlic, leek, artichoke, cauliflower, and mushrooms.

• Fruits: Apples, pears, mango, dried fruits, stone fruits, and watermelon.

• Dairy: Milk and yogurt.

• Sweeteners: Honey, high fructose corn syrup, sugar-free confectionary.

• Legumes: Lentils, chickpeas, red kidney beans, split peas, falafel and baked beans.

Refs:

Eswaran, S., Jencks, K. J., Singh, P., Rifkin, S., Han-Markey, T., & Chey, W. D. (2025). All FODMAPs Aren't Created Equal: Results of a Randomized Reintroduction Trial in Patients With Irritable Bowel Syndrome. Clinical gastroenterology and hepatology : the official clinical practice journal of the American Gastroenterological Association, 23(2), 351–358.e5. https://doi.org/10.1016/j.cgh.2024.03.047

Singh, P., Chey, S. W., Nee, J., Eswaran, S., Dietary Therapy in IBS Working Group, Lembo, A., & Chey, W. D. (2025). Is a Simplified, Less Restrictive Low FODMAP Diet Possible? Results From a Double-Blind, Pilot Randomized Controlled Trial. Clinical gastroenterology and hepatology : the official clinical practice journal of the American Gastroenterological Association, 23(2), 362–364.e2. https://doi.org/10.1016/j.cgh.2024.04.021