7 Reasons the Low FODMAP Diet May Not Be Working

Tried the low FODMAP Diet but it just isn’t working?

You’ve been living with IBS for years, struggling with horrible bloating, constipation or diarrhea. You then find out about the low FODMAP diet and are filled with hope that finally you’ve found the ‘cure.’ So, you diligently start on the diet, excited to finally say goodbye to that bloated belly, and….it doesn’t work.

This can be one of the most frustrating, upsetting feelings. You see everyone else raving about how it worked for them and you’re wondering why on earth it isn’t working for you. The worst thing is, you just can’t work out why.

If you’re feeling like this, don’t beat yourself up or convince yourself there’s something wrong with you. There are a whole host of reasons that the low FODMAP diet may not be working for you and, luckily, they all have a solution.





This isn’t exactly a reason, but I just wanted to start with checking in on your expectations for the diet. If you go into it thinking it’s going to ‘cure’ your IBS and you’re going to be completely symptom free, you’re setting yourself up for disappointment. The low FODMAP diet won’t cure your IBS. It’s not going to make it go away. This diet provides you with a strategy to manage your symptoms, so that you have control over them, which is a very different thing from curing them.

You’re unlikely to get 100% symptom relief from this diet. The overall aim of it is to help you reach a balance between adequate symptom relief and maintaining a good quality of life. ‘Adequate’ symptom relief is very subjective and will mean different things to different people. However, it’s important you go into the diet with realistic expectations around the level of symptom relief it will give you. Even if you see a 50% improvement in your symptoms, that’s huge. Don’t dismiss the diet just because you don’t see 100% improvement, as you’re then missing out on that potential 50% improvement! So, try to reset your expectation to seeing some level of symptom improvement, rather than total symptom improvement.



There are a whole host of reasons why you could be thinking you’re following the diet perfectly, but you’re actually not. This is incredibly easy to do, especially if you’re relying on dubious information from the internet and you’re not working with a health professional who’s trained in the diet.

Here are a few ways that you might have mistakenly been eating high FODMAP foods. Do you think any of them apply to you?

  • Sneaky ingredients - if you rely heavily on processed foods, you might have been eating high FODMAP ingredients that are hard to identify, like chicory root or isomalt. These sneaky ingredients get into lots of processed foods, but also things you wouldn’t expect like fibre supplements and sugar free mints. This Low FODMAP Shopping Guide will help you identify any sneaky ingredients you might have been eating my mistake!

  • Portion sizes - if you’re relying on a ‘high FODMAP’ and ‘low FODMAP’ food list from the internet, you’re likely missing the impact of portion sizes. This diet is unfortunately not as black and white as that and portion size has a HUGE impact on whether a food is high or low FODMAP. If you’re still getting symptoms on the diet and weren't aware of this, it could be because you’re highly sensitive to FODMAPs, which means the diet definitely is the right thing for you but that you need to be really careful with portion sizes. Check out this blog post to find out more about portion sizes and what to do.

  • You eat out a lot - high FODMAP ingredients (like onion and garlic) feature pretty heavily on restaurant menus. This diet also isn’t as widespread as the gluten free diet, for example, so it’s not well understood by most restaurant staff. Therefore, you might have had the best intentions, but may have been served high FODMAP food without even knowing it. Take a look at my tips for eating out on the low FODMAP diet to help with this.



Some people do see immediate improvement when they start the low FODMAP diet, after only a few days. However, this won’t happen for everyone. You’re more likely to see a quick improvement in symptoms if you suffer from IBS-D as your digestive system moves much more quickly. On the other hand, if you suffer from IBS-C, it’s likely it will take longer for you to see any effects. This is because your digestive system moves more slowly, so it takes longer for your gut symptoms to be affected.

Monash (the ‘inventors’ of the diet) recommend staying on the elimination phase of the low FODMAP diet for 2-6 weeks before assessing whether it’s worked and deciding to re-introduce FODMAPs. They’ve advised this large range because there really is a huge range in how quickly it affects different people.

So, if you’ve only just started on the diet, I’d recommend you keep going for at least a month. If you’ve already been on it that long, you need to consider some of the other reasons it might not be working for you.



Even if you’ve been diligently avoiding FODMAPs, there might be some other foods and drinks that are causing symptoms, even though they’re technically ‘low FODMAP.’


  • Not drinking enough water - can lead to constipation

  • Eating too much fat - can cause bloating, pain, wind, diarrhea

  • Alcohol - can cause indigestion, nausea, pain and diarrhea

  • Spicy foods - can cause pain and heartburn

  • Gluten + dairy - can cause pain, bloating, diarrhea and constipation

  • Medications - e.g. antibiotics, pain relief, supplements can cause various side effects

  • Caffeine - can cause pain and diarrhea

If you think any of the above might be influencing your symptoms, try cutting them out or speaking to a health professional to help you identify which ones might be affecting you.



You might be following the low FODMAP diet perfectly and eating all the right things for your gut, but you’re still feeling terrible. This could be down to lifestyle factors. The 3 that have the biggest influence on your gut are regular meal times, lack of sleep (time and quality) and stress. No matter how great your diet is, these factors can wreak havoc on your gut. They affect how food is digested and absorbed in your body, which can lead to pain, bloating, and either diarrhea or constipation.

If you think one of these could be an issue for you, try addressing it and assessing the impact on your gut. There are lots of ways to do this, but here are a couple of examples:

  • Regular meal times - try setting 'meal times’ for your breakfast, lunch and dinner and sticking to them as much as possible. Even if you’re not hungry or don’t have anything in at those times, try to have something small and nutritious.

  • Sleep quality - set a bed time and wake up time that gives you an 8 hour sleep window and try to stick to it. Also, set up a ‘wind down’ routine every night, which can include things like a meditation, some ‘me time’, shutting off technology for an hour before bed.

  • Stress - the most important thing here is to look into what the cause of your stress is and address that. If the cause is something in your life that you can’t avoid, then look at how you can deal with that stress more effectively. One of the simplest, most proven ways to do this is starting some form of meditation practice. This can be anything from breathing exercises, to guided meditation, to yoga. The easiest way to start doing this is to commit to a 5 minute guided meditation every morning. The Calm app has some really simple free ones you can try.



There are lots of different types of IBS and everyone’s version of it is totally unique. The main classifications are IBS-D (diarrhea), IBS-C (constipation) and IBS-M (mixed). The low FODMAP diet is recommended for all groups of IBS sufferers, but there are obviously going to be huge differences in how everyone’s digestion works. The low FODMAP diet may work a small amount, but you might then need more targeted help for either constipation or diarrhea. Both symptoms are very different and will require different variations of the diet.

For example, if you suffer with diarrhea, you may be even more sensitive to FODMAP sub-groups that increase the motility of your gut (fructose and polyols). Whereas, if you suffer with constipation, those same FODMAP sub-groups can be beneficial for you.

Both diarrhea and constipation can be helped by adding the right sort of fibre to your diet and the ‘right’ type will be different in both cases. This is especially important if you suffer from IBS-C, as constipation can cause your bloating. The low FODMAP diet can compromise your fibre intake as lots of high FODMAP foods are also high in fibre. So, this reduction in fibre intake can make constipation worse, and you might actually feel worse on this diet. Whether you struggle with C or D, I’d recommend adding in some linseeds and oats to your diet. These are low FODMAP and have been proven to be effective for people with both IBS-D and IBS-C.

There are a lot of other recommendations I could make here, but my best advice would be to get help from a digestive health professional, as this needs to be tailored to you and your specific type of IBS.



If you’ve followed the diet perfectly, and none of the above reasons apply to you, there could be something else at play. If you haven’t officially been diagnosed with IBS, you might actually be suffering with something else. Even if you have been diagnosed with IBS, you might have another condition which is also causing symptoms. The most relevant conditions to consider are inflammatory bowel disease, SIBO, leaky gut, endometriosis and coeliac disease. This is because they all have overlapping symptoms with IBS and they are more common in people with IBS that those without.

I’m not saying this to scare you, and I definitely don’t want you to go off and start googling all of these. However, if you think this is a possibility, I would recommend booking an appointment with your doctor just to make sure you aren’t missing something.


As you can see, there are a lot of reasons why the low FODMAP diet might not be working for you. It’s so easy to miss these reasons and to think you’re following the diet perfectly, when you’re not, so don’t be annoyed with yourself.

If there’s anything obvious in this list that you’ve not though about, try addressing it with the recommendations I’ve made. If you’re really struggling and you can’t figure out what you’re doing wrong or how to address it, find a health coach, nutritionist or dietitian who is trained in the diet and can help you figure it out. Don’t spend any more time bashing your head against the wall, trying to work out what you’re doing wrong. It's likely that there's a simple answer. And, of course, if you suspect there could be any other conditions at play here, go and see your doctor.

Reasons to consider:

  1. Are your expectations realistic?

  2. You haven’t actually been eating low FODMAP

  3. You’ve not been on the diet long enough

  4. Other food might be causing symptoms

  5. Lifestyle factors might be getting in the way

  6. You need more targeted help

  7. You might not have IBS

Thanks so much for taking the time to read this. Do any of these reasons resonate with you? Let me know in the comments.

Sophie x

Sophie BibbsComment