Updated 13th December 2023

What is the low-FODMAP diet, and should you try it?

Share this article

  • Share on Facebook
  • Share on Twitter
  • Print this page
  • Email this page

    Do you know what FODMAPs are? Many of us aren’t aware of these cryptic carbohydrates hidden in everyday foods.

    How can undigested FODMAPs cause bloating, gas, and other symptoms as they ferment in your gut?

    In today’s episode, Dr. Will Bulsiewicz, ZOE’S U.S. medical director and a board-certified gastroenterologist, teaches us about FODMAPs and how to tell if a low-FODMAP diet could be right for you. 

    If you want to uncover the right foods for your body, head to zoe.com/podcast, and get 10% off your personalized nutrition program.

    Download our FREE guide — Top 10 Tips to Live Healthier.

    Follow ZOE on Instagram

    Episode transcripts are available here.

    Is there a nutrition topic you’d like us to explore? Email us at podcast@joinzoe.com, and we’ll do our best to cover it.

    ZOE Science & Nutrition

    Join us on a journey of scientific discovery.


    [00:00:00] Jonathan Wolf: Hello and welcome to ZOE Shorts, the bite-sized podcast where we discuss one topic around science and nutrition. I'm Jonathan Wolf, and today I'm joined by Dr. Will Bulsiewicz. Today's subject is FODMAP diets. 

    [00:00:18] Dr. Will Bulsiewicz: Jonathan, we're advised to follow all sorts of diets, going dairy-free, gluten-free, avoiding fructose from fruit, or cutting out whole grains or legumes. What most people don't realise is these are all variations of low-FODMAP diets.  

    [00:00:31] Jonathan Wolf: So Will, what I want to know is, what does FODMAP even mean? It sounds super geeky.  

    [00:00:39] Dr. Will Bulsiewicz: Ha ha ha. Well FODMAP, Jonathan, is an acronym, and I'll tell you what it stands for in a second, and we'll learn why FODMAPs are incredibly important for digestive health.  

    [00:00:48] Jonathan Wolf: Okay, let's dig into all of this then and try to map out our way to FODMAPs for our listeners.

    So Will, you mentioned that FODMAP is an acronym and that tells me that there are probably a few members of this FODMAP gang. So can you tell me who's in the gang, when did they first get together, is the gang still together, and can I join?  

    [00:01:13] Dr. Will Bulsiewicz: You make it sound so cool, Jonathan. I don't want to disappoint you, but unfortunately I don't think you can join because it's a rather exclusive club. 
And also, you're not a carbohydrate.  

    [00:01:25] Jonathan Wolf: Ok, I get told often that I can't join because it's an exclusive club. Not so often that it's because I'm not a carbohydrate. I have quite a lot of carbohydrate in me. That's not enough?  

    [00:01:34] Dr. Will Bulsiewicz: You know, sadly, Jonathan, you and I, neither of us would be able to join this club and I don't think any of our listeners would either because none of us are actually exclusively carbohydrates, but you know, nonetheless… 

    The members of this exclusive gang are, I just want to prepare everyone because I'm about to use some insanely large words here; fermentable, oligosaccharides, disaccharides, monosaccharides, and polyols. Which is basically an extremely nerdy way of describing food that contains fermentable carbohydrates. And whether they be simple sugars or sugar alcohols or short chains of sugars that actually kind of resemble fiber, the FODMAP gang essentially got together in the early 2000s, when a group of scientists in Australia at Monash University first identified them and realised that there's a huge group of people that are struggling to digest these nutrients.  

    [00:02:29] Jonathan Wolf: Okay. So now you've explained that FODMAPs have just become more of a mouthful Will, and it still sounds very scientific. 

    Can you try and make it even simpler? Like what does this actually mean for my day to day eating?  

    [00:02:41] Dr. Will Bulsiewicz: Absolutely, Jonathan. So let's put it this way in terms that anyone will understand. There's five categories of FODMAPs. So I'm going to run through these and you're going to be hearing food that you probably are consuming on a daily basis. 

    So the first is fructose, which is a sugar classically found in fruit. So like watermelon, peaches, nectarines, apples, pears. 

    The second is lactose. Many people have heard of lactose. That's because you'll find it in dairy products. 

    Third are the galactans, and these are found in legumes, so things like beans and lentils and peas. 

    [00:03:16] Jonathan Wolf: And this is the first one I was like, it sounds more like it's science fiction than something in the food, so I know we're moving outside of the normal range. Keep going, Will.   

    [00:03:25] Dr. Will Bulsiewicz: Yeah, it's, well, you know, you hear it “go bean free”, right? But, maybe this is what we're talking about, right? And the same could be, oh, well “go gluten free”. 

    And that brings us to this next category, which are the fructans which you and I have discussed on a prior episode about lectins. Now these fructans, they're found in onions, garlic, but also the grains that contain gluten, so wheat, barley, and rye. 

    And then the fifth group are the polyols. And these are sugar alcohols that you may find in some plant-based foods, but you can also find them in artificial sweeteners. 

    [00:03:58] Jonathan Wolf: All right, Will, so you're starting to explain that there are like these five categories of FODMAPs. That's starting to get a little clearer. But it still seems like a really wide mix of foods. Like, I don't know, like an apple and an onion, like, and a bean. These seem like very different things. 

    So, can you explain, like, why they're lumped together? And you mentioned they can be tough to digest. Why is that?  

    [00:04:22] Dr. Will Bulsiewicz: Yeah, I mean, I think it's understandable that to the untrained eye, these may feel like very functionally different foods, but yet they are tied together by the presence of these FODMAPs. And the reason why it's important is because FODMAPs, the way that they behave, what I'm about to describe, you can find as sort of being universal to all of them, which is that FODMAPs require digestion. They have to be processed. 

    And until they're processed until we actually digest them, they're just not well absorbed in the gut. So they're able to slowly pass through the intestines. And as they do that, they're pulling water in. Now you can imagine if you pull a lot of water into the intestines, this is how you ultimately generate diarrhoea. 

    But the other thing is that FODMAPs, I mentioned earlier, are fermentable. So what this means is that if they're undigested, they eventually will reach the large intestine. And this is where our microbiome lives. And these gut microbes will actually go to work and ferment the FODMAPS, which is gas-producing. 

    [00:05:29] Jonathan Wolf: And so normally we talk about food for our microbes being great, so why can this be a bad thing?  

    [00:05:35] Dr. Will Bulsiewicz: The fact that they're tough to digest, you know, this can be an issue for people that have digestive problems or gastrointestinal problems. 

    So as they pass through and they're pulling in this water and they're producing more gas. This is how we ultimately develop symptoms and they can cause the bowel wall to stretch and, you know, the things that we think about with irritable bowel syndrome. So, abdominal pain, gas and bloating, distension, diarrhoea, and, in some cases, even constipation.  

    [00:06:06] Jonathan Wolf: So, Will, this is all making the FODMAP gang sound rather like the bad guys. 
I'm not quite as excited to join them as I was at the beginning. However, our team here at ZOE have looked into the science and there is research that shows that people following a low FODMAP diet actually had a significant reduction in healthy gut microbes which we would normally say is a bad thing. 

    So in other words being on a low FODMAP diet doesn't seem to be great. But I guess there must be some benefits if some people have been told they should be doing this?

    [00:06:34] Dr. Will Bulsiewicz: I think this is a really important point and I'm glad that you brought this up. A low FODMAP diet is only necessary for people who suffer with gastrointestinal issues. 

    So, for example, my diet could be described as high in FODMAPs. I actually, like, seek them out. I want them. I want all the FODMAPs. If you're offering FODMAPs, I will take them. I am more than happy to have them. And there's a couple reasons for this. 

    So first of all, FODMAPs themselves, they aren't inherently bad. 
When we sort of mentioned the gang in the beginning, I support this gang. And we'll get into the reasons why. But, you know, the other thing that I want everyone to know is that these FODMAPs, they actually have proven to be prebiotic, which means that they're beneficial to your gut microbiome. 

    And, you know, the other thing is that FODMAPs aren't the only thing that you will find in high FODMAP foods. 

    [00:07:31] Jonathan Wolf: I knew you wanted to be part of this gang, Will, just like me. I was, I was confident about it. So you're saying that as well as FODMAPs, there's other things in these foods? What are they?  

    [00:07:41] Dr. Will Bulsiewicz: We tend to fixate on what is the one nutrient that we're talking about, but hold up, let's see the big picture here. 

    High FODMAP foods include whole grains and legumes and fruit. And these are incredibly healthy foods because they contain fiber and polyphenols and phytochemicals and vitamins and minerals and things that nourish our body and also nourish our gut microbes. These foods are great for our gut. I mean, I would call them gut superfoods to be completely honest with you. 

    Now, you mentioned a moment ago, and I said this is an important point, a low FODMAP diet reduces healthy gut microbes. Let's come at this from the opposite perspective for a moment, Jonathan. What happens when people consume a high FODMAP diet? 

    Here's what happens. You develop a gut microbiome that has a greater diversity. This is not the perfect measure of gut health, but it is a measure of better gut health. 

    It also has been shown to increase a family of bacteria called bifidobacteria. These bifidobacteria, they are beneficial to us. They have a myriad of health benefits that include suppressing unhealthy microbes and optimizing our immune system. 
We want more. So this is why, Jonathan, I'm all about the FODMAPs. Give me all the FODMAPs. I'll take all of them.  

    [00:08:59] Jonathan Wolf: So, given this, Will, why might some people want to restrict or avoid FODMAPs?   

    [00:09:06] Dr. Will Bulsiewicz: Well, Jonathan, the researchers from Monash University who coined the acronym FODMAP, they found that by restricting the amount of FODMAPs in the diet, they could actually make people feel better if they had irritable bowel syndrome, or if they had inflammatory bowel diseases like Crohn's disease. 

    [00:09:25] Jonathan Wolf: So basically what you're saying is FODMAP diet is really for people who have these sort of digestive problems. Can you tell us a bit about what a low FODMAP diet, you know, really entails?  

    [00:09:36] Dr. Will Bulsiewicz: Definitely. And it's important to understand a low FODMAP diet is not a person, perhaps even your medical doctor, handing you a sheet of paper. 

    with a list of foods that are high in FODMAPs and then you eliminating those foods. That is not what a low FODMAP diet is. So let's break this down. 

    So, we know that these high FODMAP foods are actually quite nutritious for us. There's no need to change your intake of FODMAPs if you haven't been diagnosed with a digestive problem. 
As I mentioned, they can be full of nutrients, and many of us can eat loads of FODMAPs and be just fine. However, for those of us with digestive problems, the low FODMAP diet could be part of the solution. It's just that it can be quite tricky at first.

    [00:09:45] Jonathan Wolf: Why is it tricky, Will?

    [00:09:46] Dr. Will Bulsiewicz: So the first stage is very restrictive, and in essence, it involves cutting back on the high FODMAP foods.
In other words, eliminating them. And you're going to do this for a period of 2 to 6 weeks, whereby eliminating these high FODMAP foods, the intention is to see an improvement in your symptoms.  

    [00:10:35] Jonathan Wolf: I've actually done this, Will, and it's incredibly hard. If I remember rightly, I was basically eating sort of white rice and chicken for like three meals a day, which becomes pretty, you know, it's not much fun even by meal two, it's pretty miserable. 

    So what happens in the next stage after you've gone into that period where hopefully you see your symptoms go away? 

    [00:10:57] Dr. Will Bulsiewicz: I'm really glad that you brought that up, Jonathan, and shared your experience. So once your gastrointestinal issues stabilize, then the next step is to start to reintroduce these FODMAP foods that you have already cut out of your diet. 

    And this is done in a systematic fashion. So you go one by one, where by doing this one at a time, you are able to identify which specific FODMAPs among those five categories. Which specific ones trigger your symptoms. 

    So most people don't struggle with all of the FODMAPs. This is not an all or nothing thing. 

    Join our mailing list

    Sign up for fresh insights into our scientific discoveries and the latest nutrition updates. No spam, just science.

    This is a personalized thing like so much else in nutrition. And there are specific FODMAPs that a person will struggle with. So by going through this process, you can actually understand microbiome, and how it responds to these individualized FODMAPs. And once you build this understanding, You can narrow down the list of which ones are the problem.

    [00:11:58] Jonathan Wolf: And so the FODMAP diet is a sort of trial and error process? So you see what foods like, are having this negative impact and which ones don't have any, you know, they're just fine and then you're good to go?  

    [00:12:11] Dr. Will Bulsiewicz: You could say it that way. Once you've worked out which foods are causing these negative side effects, these digestive symptoms, then you can start to move towards personalizing your own diet. 

    So what that means is that the well tolerated FODMAPs are back on the menu. You bring them back in and reintroduce them into your diet because you know that you can tolerate them. 

    What do we do with the ones that are the problem? Well the surprise is this is not about elimination. This is certainly not about permanent elimination. This is about moderation. So these foods are good for us and remember they include a lot of important nutrients for us. We don't want to permanently eliminate them. So what we do is we restrict them to a level that we can actually tolerate. And this is something that each of us is capable of. You can tolerate these foods, it's just that we have to moderate. This is why we're using the word moderate portion size.   

    [00:13:05] Jonathan Wolf: And so, well, what sort of foods am I likely to be eating if I am ending up on this low FODMAP diet? 

    [00:13:10] Dr. Will Bulsiewicz:  You start by acknowledging that FODMAPs are carbohydrates. So they are classically in carbohydrate-containing foods, although not in all cases, like, you know, for example, dairy, this is the only carbohydrate that you will find in dairy products. 

    So by following a low FODMAP diet, in a way you are aiming to consume more foods. that are low in carbs. So this could be like more meats, fish, eggs, or like there's some that are dairy products that you're able to actually consume because they don't have a lot of this lactose. 

    So certain cheeses, right? 
The fermentation process. actually digests and pre-processes the lactose, so brie, and cheddar, and feta. And then like non-dairy milks, so like almond milk, and then like there's certain grains, so I mentioned wheat, barley, and rye are high in FODMAPs, but then there's grains that are low in FODMAPs, rice, quinoa, oats. 

    There's vegetables that are fair game on a low FODMAP diet, so, like eggplant, or as you would say, aubergine, potatoes, tomatoes, cucumbers, zucchini, or as once again, you would say in the UK, Jonathan, courgette. 

    So fruits as well that, you know, may contain fructose. So like grapes and oranges, strawberries, blueberries, pineapple. 
You can consume quite a wide range of foods. There are still a lot of choices on a low FODMAP diet. We just have to be conscious of it.

    [00:14:38] Jonathan Wolf: And so what are the warnings around this diet, Will?  

    [00:14:41] Dr. Will Bulsiewicz: It's very important to understand that this is not designed for weight loss. There are studies that suggest that weight loss can be an unintended consequence of low FODMAP diets and this is something that we see anytime a person enters into a hyper-restrictive dietary pattern. 

    When you enter into that pattern, because of the restriction, you will lose weight in the beginning. But this can have consequences. This can compromise the intake of specific nutrients, such as fiber, iron, calcium. You know, we mentioned earlier that people who remain on a low FODMAP diet permanently, it affects their microbiome in a negative way. 

    So for people who have the goal of losing weight, there certainly are better ways to accomplish this without having to subject yourself to a very restrictive dietary pattern like the low FODMAP diet.  

    [00:15:27] Jonathan Wolf: So, Will, I think we got a really great picture of the FODMAP gang and how you might approach this. 

    Before we get to your verdict, I'd actually love to share my own experiences and get your thoughts because it's very rare that I actually get the chance to do that, Will, instead of just asking you as an interested party. 

    But as I said, I have actually done this and, you know, I think as regular listeners on the show know, I got a lot of food intolerances in my early 20s after I was sick, that got better. At that point, that was before anybody had even heard of FODMAPs. But then I sort of investigated this again about a decade ago, a little bit before ZOE started. And someone suggested the FODMAP diet and I had a gastroenterologist who was also involved. And so I did this. And I think, you know, I had a couple of experiences. 

    The first is it was really hard to do. Partly just living on the restriction, because as you said, it's not just the couple of weeks it's then you're putting these things in one after another. It's slow. You've got this very restricted diet. I actually met my wife Justine at about this point and I was really low energy and she was basically convinced I was starving myself. 

    And I think that it's interesting you talk about people on weight loss. I suspect in retrospect it's hard to get enough calories, potentially just to give you all the energy because you sort of can't eat anything. What you can eat is so boring, you know, so you're not very excited. 

    I think the other thing is it's very hard to do this experiment on yourself, trying to understand really for these individual foods. 
Because it's not like just with one thing, like people, you know, you sometimes talk about gluten, there's all these foods and trying to understand what's going on can be very hard. Particularly if, you know, you have some symptoms, but they may be driven by the amount of things and combinations. So it's actually very difficult to do. 

    But I did definitely come out of this saying, Oh, I think there's some things that are really triggering this. And so I sort of cut back on that, but then introduced lots of these FODMAPs back because, just as you said, you know, the gastroenterologist and nutritionist were saying, you lose a lot of, like, all the nutrients you get in food if you don't put this in. 

    But the other thing I've taken away, because this was now probably, you know, this is before the start of ZOE, is, at that time there were lots of foods that I couldn't eat, and today I can eat all of those foods, which is amazing. And I know you went through a bit of, you know, having read your book, you went through a bit of this experience also over the last, you know, 15 years, where, in a sense, your gut was really not in good shape, so you would eat these foods, you know, I don't know, cauliflowers and raw onions or whatever, and you like really struggle with them. 

    But the truth is, you know, that's a sign of, I think, the state of your gut and your microbiome and all the rest of it. And although you can't just instantly switch this on, you know, I've definitely experienced that step by step and a lot of this has been through the ZOE experience and the guidance that I am now able, sort of like you, to eat a very high FODMAP diet and sort of seek it out and feel great about how it makes me feel. And I know if I just tried to eat that diet a decade ago, I would be feeling really sick.  

    [00:18:31] Dr. Will Bulsiewicz: I mean, you brought up so many great points and, you know, part of it is that the journey is a multi-year journey.

    So sometimes we are looking for short-term results and seeing that big picture, understanding that it does take time. But also there should be optimism that your gut is adaptable. That your gut can learn to consume and enjoy these foods. You are not rigidly stuck in a position where the food that you struggle with, you are completely incapable of consuming. It can be trained and the foods that you know, you feel like you have to moderate in the future, they could be enjoyed without restriction and you're absolutely right. 

    When I say that I want the high FODMAP diet when I want all those high FODMAP foods. 

    I didn't feel that way 15 years ago. I felt the opposite and this is part of the paradox that exists, is that these foods are in fact good for the gut. There is no doubt that these foods are good for the gut microbiome. But it is completely understandable that the person who suffers with digestive symptoms like irritable bowel syndrome, that they struggle with these foods and they think that these foods are the problem and therefore should be permanently eliminated. 

    And what we're here to say is that you don't need to permanently eliminate these foods, but there is a process that you can follow to work these foods back into your diet. So that you can enjoy them without restriction and actually get the nutritional benefits in addition to the flavour profiles that they bring, which is, you know, an added thing that I like. So I think that there's a lot that's good there.  

    [00:19:57] Jonathan Wolf: I love that, Will. And as you were saying that, I was just thinking, my little girl has just learned how to ride her bicycle, which is like a big milestone. And the analogy I'm thinking about is, you don't just put your child on a bicycle like the first time ever and then just push them off and expect them to be able to ride, right? 

    Like, you know that's going to end up with them crying on the ground and it's a process and you know these days you can even ride, you know, start with a bicycle, with like a balanced bike with no pedals, which didn't exist when I was little, and that's what happened with my daughter, which was like this amazing way, but she was on that for a long time. And then she, you know, she switches to the pedals and that still takes a little while to get. 

    And I feel like there's something like that as, as we're thinking about your gut, which is for most of us who probably grew up eating this Western diet, you know, super processed, very little fibre, very limited amounts of vegetables, a lot of things in it that you know, we now think of as ultra-processed food and probably causes a lot of issues, you know, very cut off from nature, all these sorts of things. 

    You can't expect to suddenly jump and it's like saying like, Oh, I'm just, here's a bicycle. You're just going to ride it instantly. Like, you know, that's not going to work. And so there's something about this being a, being a process, which I've definitely experienced myself. And I guess I just sort of feel like perhaps that's a useful metaphor. 

    [00:21:19] Dr. Will Bulsiewicz: Yeah, I love that. It is a process. In a way, our gut almost needs to learn for the first time or relearn to consume these foods because they largely have been stripped from the diet that we were all raised on. 

    But much like your daughter learning to ride a bike, when you reach the point where your gut has matured and its ability to handle these foods, you get to ride off into the sunset and enjoy a bike ride. 
And you know, the hope would be there's no turning back.  

    [00:21:52] Jonathan Wolf: So, well, having said all of this. As a gastroenterologist, like what's your verdict on the FODMAP diet? 

    [00:21:59] Dr. Will Bulsiewicz: Well, I think that the verdict is once again, we have emphasized that this is about people who have digestive symptoms. So if you don't have digestive symptoms, then I really don't see why you would ever be entertaining the low FODMAP diet. 

    If you do have digestive symptoms, it's possible that you may find benefit and improvement of those symptoms by following a low FODMAP diet. But as we've emphasized, this is not just a restriction of FODMAPs, it's certainly not a permanent restriction. It's really important to understand that this is ultimately about building up your gut like a muscle, making it stronger, and having enhanced abilities to process and digest these foods, which can be done. 

    And that process may take time, and it also may require the expertise of people who are facile in these concepts of the low FODMAP diet. And this is why I'm a big believer and supporter, much like you did Jonathan, in people seeking out help such as with a dietitian.   

    [00:22:54] Jonathan Wolf: I think if you are doing this, then obviously, firstly, you should probably be starting off talking to a doctor if you've got really bad symptoms, and secondly, I agree that I did this with a dietitian, with a nutritionist, and I think that it'd be almost impossible to sort of do the FODMAP diet sort of safely and well, unless you're guided. 

    Because I think you could easily end up being really malnourished, right, where you're just basically eating like rice and chicken and white bread and you're going to get really sick. 

    So I think this is an example where, of course, like the food we eat is so important for us. So if you suddenly start to cut it all out, you know, you can have profoundly negative impact in the same way that if you add all the good stuff, I believe obviously you can have great impact.

    [00:23:42] Dr. Will Bulsiewicz: Completely agree. 

    [00:23:43] Jonathan Wolf: Well, Will, I think that is much clearer for me. I never really understood what I did, and now I think I do understand what it was. I hope it's much clearer for our listeners. Thank you for navigating us so well through this rather complex story of FODMAPS.  

    [00:23:47] Dr. Will Bulsiewicz: Oh, it's my pleasure, Jonathan, and thank you to our listeners for being with us today. 

    [00:23:51] Jonathan Wolf: If you want to understand how to support your body with the best foods for you, then you may want to try ZOE's personalized nutrition program. You can learn more and get 10% off by going to zoe.com/podcast. I'm Jonathan Wolf.

    And I'm Will Bulsiewicz. Join us next week for another ZOE podcast.

    Share this article

    • Share on Facebook
    • Share on Twitter
    • Print this page
    • Email this page