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FODMAPs, Vegetables, and IBS

FODMAP Veg title

If you have read our previous posts on ‘FODMAPs & Fruit, or ‘The Low FODMAP Diet, you might want to skip over the intro below if you don’t need a recap. If you’re new to learning about the FODMAP diet I’d recommend also clicking on those other posts and having a read as they complement the below information!

The Low FODMAP Diet is designed to help sufferers of IBS reduce and manage their symptoms. It was designed to be implemented in 3-phases, with the end goal of balancing the least restrictive possible diet with the greatest sustainable improvement in symptoms. 

Phase 1 is the low FODMAP phase where Fructose, Oligosaccharides, Disaccharides, Monosaccharides and Polyols are restricted from the diet to relieve symptoms and create a baseline to operate from. Suitable alternative foods should be found to replace those being restricted. It usually lasts for 2-6 weeks.

Phase 2 is a phase where the FODMAPs are individually tested to establish tolerance levels to specific foods. This process can take a significant amount of time as there are a lot of variations in the types of FODMAPs, serving sizes, and foods that need to be trialled. It usually lasts for 6-8 weeks.

Phase 3 is the longer-term application of the information gathered in phase 2. A more personalised FODMAP diet is established which incorporates as many well-tolerated foods as possible, while only restricting and replacing poorly tolerated ones. FODMAP tolerance can change over time, so foods that weren’t initially tolerated can be tried periodically.

The Types of FODMAPs in vegetables.

Of the 5 FODMAPs, mannitol and fructans are the main types present in vegetables, and these need to be tested during phase 2 of the FODMAP diet. Other FODMAPs often found in vegetables include sorbitol (e.g. found in green capsicum) and galactooligosaccharides (e.g. beetroot).

Above is a summary of which vegetables are high in FODMAPs. These are not suitable for phase 1 of the diet and are most likely to cause symptoms in those who are sensitive to them. The list is not completely exhaustive so there may be some vegetables missing. A good tool that you can use to help determine the FODMAP content of foods is the Monash FODMAP app.

After phase 1 of the diet is complete, these higher FODMAP foods can be trialled to identify which ones, and how much of each can be safely added back into the diet.

What Vegetables are low FODMAP?

As you may know by now it is always a priority of the FODMAP diet, to replace foods that are being restricted with alternatives of similar nutritional value.

Vegetables are especially important to help maintain good health and have been linked with lower incidences of cardiovascular disease, overweight, obesity, high blood pressure, and type 2 diabetes. 

Eating the recommended number of vegetables is also the best way to ensure nutrient deficiencies do not develop. Australian Dietary Guidelines state during ages 19-50 men should be aiming for 6 serves of vegetables per day, and women 5 serves. 

Unfortunately, as can be seen from recent Australian census data, the vast majority of adult Australians (92.5%) do not meet these guidelines. 

Vegetable intake of Australians

When in the restrictive phase 1 of the diet, it is important to remember vegetables are an excellent source of nutrients including almost all of the necessary dietary vitamins, minerals, and antioxidants. Vegetables should still make up the largest part of your diet.

The below image features a list of some vegetables which are low in FODMAPs in some typical serving sizes.

Low FODMAP vegetable List

Similar to fruit and other FODMAP foods, there is typically a dose-response relationship with food and symptoms – but as seen above there are many examples of low FODMAPs vegetables which are typically suitable to use as substitutions for high FODMAP vegetables.

Which Vegetables Are Good For Phase 2 Challenges?

Phase 2 food challenges are when individual tolerance to FODMAP-containing vegetables are tested. It is important to remember some vegetables contain multiple FODMAPs – i.e. both mannitol and fructans. Multi-FODMAP veggies include some mushrooms, white onion, asparagus, beetroot, fennel, snow peas, and butternut pumpkin. Such vegetables would not be suitable for initially testing the response to just mannitol or just fructans in phase 2.

For example, if someone wanted to test tolerance to fructans a white onion would not be suitable to do so as white onion also has both fructans and galactooligosaccharides which may cause symptoms. This can incorrectly give the impression that fructans were the cause, resulting in the unnecessary restriction of fructan containing foods.

A red/Spanish onion, on the other hand, would be a good food to test fructan tolerance, as it is high in fructans, but not in other FODMAPs. 

Green capsicum (AKA bell pepper) would be a good food for testing sorbitol as it is the only FODMAP found in this vegetable.

Portobello mushrooms would be a good choice for testing mannitol tolerance as they are high in mannitol but not in other FODMAPs. As mentioned earlier, there is a strong dose-response relationship between the amount of a FODMAP that needs to be eaten to trigger symptoms.

Taking the example of Portobello mushrooms:

  • 10 grams is considered low FODMAP 
  • 15 grams is considered to have a moderate amount of mannitol
  • 75 grams is considered to be high in mannitol

During the challenge phase you may find that you have no symptoms when eating 20g, but eating 75g gives you symptoms. This might indicate you have a moderate tolerance to mannitol-containing foods, but not a high tolerance. Having established this level of tolerance, you would then move on to testing a different FODMAP/food.

Key Concept: if you use food to test one type of FODMAP, and you do not have a symptom response, it means you are ok to eat any food containing that FODMAP group.

For example, if you have no symptoms after eating mushroom to test mannitol, this means you are ok to eat mannitol. The source of the mannitol does not matter.

To put it another way, cauliflower is considered a high mannitol food but is free from other FODMAPs. The mannitol found in cauliflower is the same as mannitol found in mushrooms. If you are fine with mushrooms you don’t need to then go through the testing process again with cauliflower.

As with testing any FODMAP group, this may sound complicated…the FODMAP protocol can be difficult. This is why guidance from a qualified dietitian is always recommended when undertaking the FODMAP diet.

A list of dietitians who are well qualified to help guide you through the process can be found in this list of Monash University approved FODMAP dietitians

As mentioned earlier, the Monash Low FODMAP Diet app is also a great smartphone tool for helping navigate the ins and outs of the diet, and includes a comprehensive list of foods and serving sizes containing the various FODMAPs. 

Remember the overall goal of implementing a FODMAP diet is including the widest variety of foods possible for that individual. Every individual will have different tolerances that will be discovered throughout the FODMAP challenge.

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