Welcome to episode 66 of the Inside Knowledge podcast for people with IBS. I’m Anna Mapson. This week I’ve picked these three diets that I often see promoted in Facebook groups or online forums where people are desperately seeking help for their digestive issues. So these might be things that you’ve considered.
Two opposite diets for IBS
Maybe you’ve been tempted by the promise of cutting out all these foods that could potentially be leading to digestive issues. Like bloating, constipation, diarrhoea, gas. Maybe the thought of not eating any of those foods is really tempting. And you’ve thought about one of the fibre restricting diets like the carnivore diet or keto.
The other thing people do is try and go really ‘clean living’. I kind of put those in inverted commas as I’m speaking. And try and go vegan and cut out meat and fats. Go very low fat, kind of plant based diet. That’s the alternative approach.
Restrictive diets for IBS aren’t recommended
Today, we’re going to go through those in a little bit more detail and full disclosure, I am going to up front say, as you may find by the end of this podcast, I’m not in favour of any of these three in order to improve IBS symptoms.
What you will find, is that some people individually may have a small improvement. I can explain to you why that might be. However, when we look at the evidence, and when we actually understand the biological mechanisms by how these diets are working, in the long term, you will see that there are additional risks.
Restrictive diets can affect relationship to food
And at the end, I’m going to kind of wrap it all up just by talking a little bit about some of the things that these very restrictive diets have in common. How that might also be affecting the your relationship with food. Your relationship with your body, and enjoyment of eating.
Ketogenic diet for IBS
I’m going to start with the ketogenic diet. This is where you basically cut out all carbs or you restrict carbs to between 20 and 50 grams per day which is very, very low.
So this is reducing any foods that have starch in them. Like grains, any legumes, beans, pulses, root vegetables, sweet corn, potatoes, fruits. Any of that you’re removing. You’re mostly focusing on fats and meat. Lean protein, but also high fat foods.
Ketogenesis – burning fat
The way that the ketogenic diet works is that when your body doesn’t have access to glucose, your liver will start to change fats into ketones. Ketones are used as energy for the brain. In all our cells, we can use ketones instead of glucose. And this normally happens within about three days of starting the diet.
It’s the same kind of principle as things like the Atkins diet that have been around for years and years. And this is just the new version of it.
Ketogenic diet origins
The ketogenic diet actually was developed to help children with epilepsy by managing their glucose control. That is what it has been specifically tested for and designed for, was to manage epilepsy in children.
Why you might feel better on keto
Some people with IBS may feel a little bit better on this diet because you’re naturally cutting out nearly all the high FODMAP foods, And if you don’t know what the FODMAP diet is, go back and listen to episodes 17 and 18 where I explain it a lot in more detail.
But basically, it’s a lot of vegetables, fruits, grains. You may find a reduction in fermentation of these fibres by reducing them in your diet.
So you might find less bloating, maybe less diarrhoea, because you’ve cut out a lot of those things that can be triggering your symptoms. Also, some people report changes in their blood glucose management through burning fats instead of burning glucose.
Sometimes having a higher fat diet people feel that they’re getting more steady energy because you’re not having those peaks and troughs of high blood glucose coming from a meal and then dipping again as the glucose is put into the cells.
High fat diet
Because the diet is so high in fat and that is one of the key points of this diet, you are very likely from the research to increase your low density lipoproteins. That’s your bad cholesterol. That is the cholesterol that we do not want to see raised. And actually is strongly associated with risk of heart attack and cardiovascular issues.
We know that eating higher saturated fats diets will lead to higher LDL. And you don’t want that. It’s also worth saying that I think the research is pointing to the fact that people may have better glucose and insulin tolerance whilst they’re on the diet. But that is just because they are not eating any glucose.
It’s not changing their underlying physiology. Or it’s not changing the way that they metabolise sugars and insulin. It’s just cutting them out of their diet. Changes in their blood markers are only relevant when they’re following that particular diet.
High cholesterol risk
Those are some of the cardiovascular issues with following this diet and it’s massive. I don’t want to underplay that. Partly the reason why I would never recommend anyone goes on a high fat diet because of the Impact on your cardiovascular health. You won’t feel your LDL rising. You won’t notice that you’re getting bad cholesterol It’s just that cumulative over time and in time can lead to some significant health issues.
So with that put to one side because we’re talking about IBS and SIBO here, the other thing about high fat diets is that fat is typically a trigger of IBS.
High fat diets and IBS
For some people who have IBS, depending on what your issues are and your particular symptoms, You may find that high fat diets may lead to constipation and that’s because our body naturally slows down digestion when we’re having high fat, high protein meals which you’re mostly eating in keto.
The other thing is some people may find very fast transit and actually accelerated diarrhoea. Speedy transit because you may not have the ability to process fats properly. So for some people, it will go one way, constipation. Other people may find they get worse diarrhoea.
Those two are significant reasons why I don’t think the ketogenic diet is suitable for most people with IBS.
Ketogenic diet and leaky gut
I will put a link to all of these studies as well, but I found a 2023 study. In people where they, looked at a ketogenic diet for people who had obesity and were looking to lose weight, but the key thing they were measuring in this dietary intervention was the intestinal barrier function.
Something you might hear me talk about in this session quite a bit is the impact on our gut microbes. This wasn’t specifically looking at reduction in starches that feed the good gut bacteria. What it was looking at was changes in the intestinal permeability. That is how many of the foods that they were eating, the tiny particles, were getting into the tissues and through the tight junctions between the gut cells. Rather than being absorbed into the gut cell in order to be properly metabolized by our body.
Keto diet lead to intestinal permeability
This study took 24 people who were obese and were looking to lose weight and they cut down their carbs significantly. What they found is that they had higher levels of lactulose and the mannitol ratio. So the way that they measure this intestinal permeability, and this is used in other studies as well, is they will look at how much lactulose is excreted in urine compared to how much mannitol. These are two types of sugars. And how much of each of them is being excreted in the urine.
So ideally, lactulose doesn’t get into the urine, it just goes through the gut and comes straight out. It might be metabolized by gut microbes along the way, In this, the people who followed this very low carbohydrate ketogenic diet had an increase in their intestinal permeability.
Keep an eye on inflammation
That could be exacerbating gut inflammation in the long term, and is definitely something to be aware of. In the ketogenic diet, you may also eat some low starch vegetables such as Spinach, you know, salady things that are not very starchy. You can include some vegetables, which is going to give you some degree of antioxidants. Vitamin C, and some of those really core nutrients.
Carnivore diet and IBS
The next stage up from the ketogenic diet in terms of strictness, I suppose, is the carnivore diet. This is where you literally only eat meat and animal products and have no vegetables, fruits, grains, anything else except meat and fish and eggs. I think they can have butter,
We don’t have any research, really, into IBS and the ketogenic diet.
And that is probably because there are very few research studies that would pay to do this investigation because it just defies most common sense that eating just one food group is going to be healthy. It wouldn’t be probably ethical in lots of ways to put people through this diet.
Changes to the gut microbiome
However, there is one study from 2014 that took a small group of healthy men and put them through an animal only diet for a few days and then switched and they went through a plant based diet only diet for a few days. Now, the difference is those people were healthy. They didn’t have IBS, but what is really interesting is that they had dramatic changes in their gut microbiome and they had an increased growth of inflammatory bacteria.
Now, when I say inflammatory bacteria, we don’t necessarily know that having one type of bacteria will give you X, Y, Z symptoms. We don’t really have that level of correlation between certain symptoms and certain bacteria.
However, we’ve got a sense, I think, growing over the last 10 years, that there are certain profiles, if you have the majority of these type of bacteria, you’re more likely to have digestive issues.
Inflammation linked gut microbes
There was one particular bacteria that is strongly associated with the development of inflammatory bowel disease. And in 5 days, on a carnivore ish like diet, the men in the study had dramatic increases in Bilophila wadsworthia. This is strongly associated with people who have Crohn’s and ulcerative colitis.
And of course, Over the few days, because they were not eating any fibre, the men also had significantly lower levels of short chain fatty acids. Which are anti inflammatory, kind of good molecules that are by products from our gut bacteria. Used as fuel for the colon cells. They’re really good, they circulate around the body.
Increased secondary bile salts
They had lower levels of that, but that’s natural because you weren’t feeding the bacteria that produced them. They also had more production of secondary bile salts, which are known to be very irritating to the colon as well. As you get secondary bile salts increasing, which can happen when you’ve got bile acid malabsorption,
Listen to episode 52 for more information about bile acid malabsorption and diarrhoea or see this blog post about the forgotton cause of IBS-D. But what is really interesting is that these changes were pretty quick.
The people in the study, although it was a tiny study, it was 10 years ago, it was only 10 people, in a couple of days they noticed changes in their gut microbes that could have potentially led, longer term, to changes in digestive symptoms.
So, I think that is one of the main reasons why I would never suggest that people follow the carnivore diet.
Removing fibre from your diet
The reason you might find it helpful Is that again like with the ketogenic diet you are cutting out all of the fermentable starches.
But just think about that the fermentation happens by good gut bacteria as well as bad bacteria. You are removing the food source for all the good bacteria in your large intestine that do good work.
They interact with your immune system. They help you with your motility, they help to keep the gut lining healthy with good levels of mucus. So you don’t get so irritated by food. These are really important. We need good levels of healthy bacteria.
Gut microbiome is essential to health
It’s not just about fibre producing a good bowel movement. The gut microbiome is a bit like an organ in and of itself. They’re actually really critical to look after and think about the health of them. They’re an ecosystem that relies ideally on a good diverse diet.
Is a vegan diet good for IBS?
The third diet I want to cover is the vegan diet and in a way it’s a bit more tricky. Because just being vegan doesn’t necessarily mean you are eating a good level of plants and a good high fibre diet.
As you might have remembered from my previous case study episode 58, when I talked about a vegan with a slow transit constipation. She was actually eating a vegan diet but was not really eating a healthy diet.
Vegan doesn’t automatically equal healthy
There was a lot of fast food and takeaway things in there. It’s actually quite a low fibre diet. We shouldn’t automatically assume that people who are eating vegan are necessarily eating a higher fibre diet. However, it is mostly correlated with that, just because they’re eating a lot more plants and tend to eat more grains as well, which are higher in fibre.
What you might find on a vegan diet is because of this higher level of fibre, they’re actually having more bowel movements, so a quicker speed of transit time. And that can also then impact on gas levels because of the fermentation of the fibre by gut bacteria.
Eating vegan protein with IBS
One of the main problems with the vegan diet for people who have IBS is achieving enough protein. Because you are very reliant on beans and pulses. As well as tofu.
Without any animal products, it’s very tricky to get enough protein without including some of those most highly fermentable foods that are going to cause a lot of bloating and gas in most people.
Like beans and pulses, even tofu to some extent when you eat a lot of it, may be contributing to some of your IBS symptoms So this is why following the vegan diet is very tricky when you have IBS. Now, I know for some people it is an ethical choice. It’s about environmental reasons or animal cruelty all of those things.
Choosing a vegan diet
So it’s not necessarily a dietary choice for reasons that you think it’s a good healthy diet. Although some people do choose a vegan diet because they feel it’s better for them because they’re eating so many plants.
Sometimes, people I work with have chosen to stop being a vegan for a short while while they get their IBS under control. And then they can revert back to different ways of eating if their digestion feels better.
There really isn’t much evidence about using a vegan diet in IBS and whether it is good or bad. I’ve seen some recent studies.
In fact, there was one out just this year showing that going vegan or just eating more plant based diet for a set amount of time did not make any negative bowel changes.
Vegan diet may increase bowel frequency
There’s also been a few studies in the short term showing that there is a small increase in bowel frequency for some people on a purely plant based diet, but we really don’t have a good evidence base.
What I would base my presumptions about it not being a great diet is people I’ve worked with. And just the way that I know high fibre diets or plant based diets can work because you don’t have the balance of having more animal proteins in there.
What is the best diet for IBS?
So where does this leave us all? We’ve been through three different diets. We’ve got the carnivore and keto diet on one side, really focusing on protein, animal fats and no fibre. And then on the other side, we’ve got like the purely plant based, high fibre diet.
And in reality, neither of these is ideal for people who have IBS.
There’s certain key nutrients that are removed from all of these diets. And, wherever possible, I do try to get people to eat a broad and balanced diet. With as much variety in as possible. And that’s variety in your types of fats and proteins and fibres and carbohydrates.
That’s why These diets are not ideal for IBS.
Restrictive diets can change your relationship to food
The other thing that you will find with these kind of diets is that they have a lot of strict rules. You have to be 100 percent compliant to the diet in order for them to work. With the keto diet, you only go into ketosis when there is no glucose in your body for a couple of days. So only when your glucose is very, very low.
For a number of days, will you start to use ketones? Until that point, if you are suddenly having a biscuit, or you’re just caving in and having a little bit of bread or potatoes, you will be cycling between glucose and ketones. That will leave you feeling very depleted anyway.
Obviously the same with vegan. You’re either a vegan or you’re not. And if you’re not completely vegan, then you’re more like a plant based meat eater or a vegetarian. Also, these are fine, but it’s not vegan. So if you’re going to be vegan or ketogenic or carnivore, these have got some very strict rules.
Obsession over food
And another problem that we run into when we follow very strict dietary guidelines is people become, tend to become quite obsessive about the food that they eat, where and when they can eat, and also what is happening to their body.
There’s a lot of extra thought about food because you have to in order to follow those rules. That in itself might not be a problem for everybody but it can lead to obsessive thinking which can then lead to more disordered eating practices.
It’s also much more difficult to eat with other people socially. Particularly if you cook or eat with others in the same house. That can lead to a lot of difficulties when you’re trying to cook the same food and not everyone eats the same.
Are food rules causing your to be less social?
Sometimes, because you are looking at that 100 percent compliance with these kind of meals, it means you will miss out on eating with others and socialising. And some of the joy in eating as well, it becomes very rule bound, and the more rule bound eating we see, there’s a tendency that you can develop some more obsessive thoughts about food.
Which really isn’t healthy, and ideally, you just want to eat without so much pressure, I suppose.
Omitting key nutrients
The other thing, going back to the key nutrients that you are going to be missing by following these rules. Obviously the vegan diet, you are low on B12. Because there’s none from animal sources. Possibly low as well on calcium, iron, vitamin A, and omega 3, because these are often sourced from animal products. So, vegans can be low in those.
Ketogenic and carnivore diets definitely are low in fibre. But because you’re emitting so many different fruits and vegetables in the carnivore diet, you will have no vitamin C. No antioxidants coming from the plant food matrix. So you’re removing all of that, as well as removing the fibre that we’ve gone into already.
So, that is another reason why these diets are not ideal for people with IBS.
In summary
I know it’s really tempting when you see people online saying, yeah, I went carnivore and all my symptoms disappeared. That may be the case in the short term, but I really just urge you before launching into any of these diets in order to cure your IBS. Or to deal with your symptoms, to think about the long term consequences of cutting out so many vital elements of our diet. And trying to think about how you can manage them in a different way. I hope this episode has been helpful.
If you’ve got any questions on any of these three diets and what it might mean for you, please drop me a line, Or you can look me up on Instagram where I am @goodnessme_ nutrition.
I’ll leave it there for this week. Thanks very much for listening to this episode of The Inside Knowledge. Better digestion for everyone.