ZOE Science & Nutrition - Recap: Simple ways to improve gut health today | Dr. Karan Rajan

Episode Date: September 16, 2025

Research continues to confirm how important the gut is for overall health. From energy to immunity and even mood, it all seems to start with the gut. It’s no surprise then that the hunt for the next gut boosting hack has exploded in recent years. So, are probiotics really the answer? Or is the fix already sitting on our supermarket shelf? In this episode, Dr. Karan Rajan helps us separate science from marketing hype and shares the simple, evidence-backed changes that can make a big difference to your gut. 🌱 Try our new plant based wholefood supplement - Daily30+ *Naturally high in copper which contributes to normal energy yielding metabolism and the normal function of the immune system 📚 Books from our ZOE Scientists: The Food For Life Cookbook by Prof. Tim Spector Food For Life by Prof. Tim Spector Every Body Should Know This by Dr Federica Amati Free resources from ZOE: Live Healthier: Top 10 Tips From ZOE Science & Nutrition  Gut Guide - for a healthier microbiome in weeks Have feedback or a topic you'd like us to cover? Let us know here Listen to the full episode here

Hello and welcome to Zoe Recap, where each week we find the best bits from one of our podcast episodes to help you improve your health. Today we're diving into one of our favourite topics, gut health. Research continues to confirm just how important the gut is for overall health. From energy to immunity and even mood, it all seems to start with the gut. It's no surprise then that the hunt for the next gut-boosting hack has exploded in recent years. So, are probiotic's really the answer, or is the fix already sitting on our supermarket shelf? In this episode, Dr Karan Rajan helps us separate science from marketing hype and shares the simple evidence-backed changes that can make a big difference to your gut.

When we talk about the gut, we're not just referring to the stomach, are we? No, and in fact, if you're thinking about the gut, you think about digestion. and if you think about digestion, it would also be wrong to think about the stomach because no digestion actually really takes place in the stomach. There's some mechanical and maybe some chemical digestion. It also happens in the mouth. But actually, digestion begins in the brain. So when you're even thinking about an ice cream, a plate of food, the brain actually triggers that whole cascade of digestion. You know, the signals get sent to the gut, to the saliva glands in your head and all these juices are beginning to, you know, starting to be

secreted. And that's all linked with also your circadian rhythm, that biological clock. You see, I like to think of the gut as this orchestra. And that orchestra, the maestro of that orchestra, is the brain, the circadian rhythm, because it determines when you feel hungry, when you want to go to the toilet. So it really all starts in the brain. And then the bulk of the digestion, the kind of real mechanical digestion and the chemical stuff that we think about, then occurs in the small intestine. That's where the bulk of it happens. So really, the stomach is such a small player in the grand scheme of things of gut health and digestion. And even beyond the small intestine where I've just said digestion occurs, it's really, if you want to dig down into the granular detail,

the colon, where the bulk of the ecosystem of our digestive activities takes place. And that's where the microbiome live. When you're thinking about advising people about what they can do to make their guts happy. What do you say? And maybe we should start with food, but then I'd love to discuss some of the other things that you talk about as well. Yeah, I think it does start with the food,

a lot of the at least easy options that someone can make a change from right now, listening to this podcast from tomorrow, from today, even making that change. And we know the gut microbiome is quite adaptable. It bounces back relatively well. And it's very responsive to change. So even within 24 hours of eating a certain food,

you can begin to see some change. in the microbiome. So, you know, if you look at most of the, you know, literature that's out there, the meta-analysis and the systematic reviews, when it comes to eating for better gut health, it's nothing very complicated. If you break it down into, you know, we talk about fiber and prebiotics, they're essentially the fertilizer for the bacteria, allowing them to thrive. So, you know, plant-based foods. Now, it doesn't mean you need to have a plant-based diet full stop and cuts out every single piece of meat or fish. That's, you know, not the case. You can have a perfectly thriving microbiome with meat.

But the majority of the diet, if it is plant-based, that's good. And I think even a lot of the Zoe data, which published a few years back, suggested that magic number to be around 30 grams of fiber a day. And I think getting not just that target in mind as that number, but also an abundance of variety as well. And a lot of the studies suggest that the diversity comes from the colours. because the colors are linked to, you know, varying levels of polyphenols, which are antioxidants, natural phytonutrients, plant chemicals, which provide this sort of anti-cancer, anti-inflammation effect. That's what antioxidants and polyphenols are. And that helps your gut, ultimately. And all of these fiber-rich foods, apart from providing various nutrients, vitamin C, vitamin A, etc,

also provides that basics of the fiber, the solubles and insoluble fibers, which, We can't deal with with our normal digestive enzymes, but the bacteria, which we host in our colon, their enzymes, the bacteria enzymes, can deal with that and then ferment those fibers which we can't process to then churn out other beneficial nutrients like vitamin K, B12, and much, much more. And a lot of these chemicals, particularly things like butyric acid, butyric acid is a short-chain fatty acid, which is very beneficial for the gut lining and the gut health in general. So all of these sort of basic things, colourful foods, diversity and fibre, those are the kind of very, very basics.

And all of that interesting is basically about feeding your microbes to then support your health. So it's interesting that all of the things you've described so far when you're saying, how do I have a health to the gut and hopefully reduce my risk of these symptoms. It's interesting. You're very focused, in fact, on supporting your microbiome. Is that a fair playback? Yeah. I think, you know, more so than worrying about, you know, adding more good stuff. stuff to your garden and adding more flowers to your garden, that's not sustainable unless you actually tend to the existing wildlife and, you know, flora and fauna that exists right there right now.

And that's the best strategy you can do. So if you've planted all of these wonderful flowers, you need to take care of those instead of, you know, just adding more good flowers and forgetting to water the ones that are there. I love to hear you talk like this because I am reminded, as I said, about 25 years ago, my experience seeing quite a lot of doctors in the UK with the cintas I have and just really no thinking at all about this idea that you have the microbiome that you need to feed it. And what's interesting is that, you know, I've been on a long journey with my own health and my symptoms got much better through my twenties and thirties. And interestingly, were triggered by an illness at the very beginning,

which is something you mentioned could possibly happen. But one of the things I've been really struck is since I started Zoe and started working with all these different nutritional scientists, you know, my diet has changed a great deal and it's made an immense difference to how I feel. And I never would have believed that that was possible. So I find there's something really wonderful that, you know, there are doctors now sort of talking about this. I do want to ask a bit because I think you were just switching there

to contrast, I think, eating food with sort of probiotic supplements, right? Eating something which says it has bacteria in it. And I want to come back to that, you know, the question right at the very beginning. what are your thoughts on probiotic supplements? So I've prescribed probiotics to patients limited over my career, but these are medical-grade probiotics, have specific strains, you know, lactobacillus usually, which is one of the most highly studied strains of bacteria

when it comes to probiotic research, and they have the right number of colony-forming units, so the right concentration, dosage, etc. And again, when we prescribe them, we don't prescribe them with the absolute guarantee and belligerent confidence that they will absolutely work. They might work for a specific subset of people with conditions. So certain infection associated, you know, antibiotic associated infections, maybe certain subtypes of IBS and certain post- bowel cancer or bowel surgery states, they may have some effect. We don't

really know, but there is some evidence they may have some effect. So when you then contrast that with consumer-grade probiotics that's available for the public in your local supermarket, there is no way to guarantee that has an effect for a multiple number of reasons. One being that our microbiomes are so unique, you know, as unique or more unique than our fingerprints. So how can we expect an over-the-counter one-size-fits-all supplement to work for every single person? It's one argument. The second argument is in the UK and in the US as well, these are regulated as foods and supplements, not medicines. They don't have to go through the rigorous medical testing and trial testing.

So actually, these probiotic supplements, you know, juices and drinks, don't have to actually back up any evidence that they, you know, purportedly claim in their bottles. Do they actually have live strains of any of these? Do they have the right number of units? They can claim all these wonderful things like immune boosting and clarity in focus. None of that has to be backed up at all. That's rather depressing. It's very depressing. And what's even more worrying is that I was of the opinion that, you know what, it's harmless.

It probably won't work, but it's harmless. So if you want to take it, you're just wasting money. Go ahead. But actually, I was wrong. It's not necessarily harmless because there is actually, you know, a few research papers out there suggesting that if you add in all these probiotics, if they are alive, what if they overcrowded existing good ones if they do end up colonizing. What if they end up colonizing in the wrong place and causing small intestinal bacterial overgrowth? What if they do cause more harm?

What if they contain contaminants? So actually, you know, more so than money, there is published evidence suggesting there could be risk as well. And one final thing I will just say on that as well, there was one interesting study I read which suggested that a lot of these bacterial strains put into so-called probiotic supplements are genetically engineered. And they could be, you know, harmful in a way that it contributes to antibiotic resistance. Because, you know, these are, again, genetically modified, and bacteria transfer their genetic information by a horizontal transfer. That's one way, apart from mutating.

So they could transfer some of the genetically modified genes to, you know, bacteria which already are inside us that we host, could increase the risk of antibiotic resistance. that's definitely a concern. I can tell you're definitely not very keen on people going down to the local grocery store and popping a probiotic. I wouldn't be. I think I'm optimistic in that we will get to that point in science where actually that's a viable option, where we have tailored probiotics or even generic probiotics, which actually do work.

But I don't think we're there in the science where we can actually say, just like we recommend vitamin D in winter months. Actually, yeah, we recommend probiotics for general health. I think we could get there in the next few years, maybe, but right now I don't think it's worth it because there are so many other low-hanging fruits. I think there have been two things have been quite eye-opening for me.

The first is because we can now do this sort of shotgun sequencing of the microbiome, so we can actually understand like the individual microbes that are inside your gut, and then from that figure out which are really the good ones, and I describe that, you know, we now have this panel of sort of 50 microbes that we've identified as good microbes. What's interesting is these probiotics you buy, they don't have a single one of those 50 good microbes, which was shocking to me. And what I've understood now is it's really hard to grow the microbes that are inside your gut

because they like to live in a place with like no air and they're managed by your immune system. Like it's a very special environment. Whereas the probiotics that you can easily grow and therefore sell, like, well, they just live in the air. And so you end up with these things that tend to, you colonize a yogurt well, but it's not necessarily the thing that's best for your gut. And the other thing that was really interesting to me is that when I broke my toe, I called up two scientists and doctors who were associated with Zoe, Tim Specter, and Will Bolshewitch. And basically, after all of this, they said, Will said, well, there's one probiotic

that I think in this particular situation you might try, which is actually yeast. And Tim was like, oh, I actually wouldn't take any, I would just go all out on fermented food. And I was fascinated that, like, the cutting edge insight was so far away from what I had started with, which is this assumption that, well, you know, just pop these probiotics. So there is like a really big gap, I think, between, I guess, what's been sold today and it seems to be where the scientific evidence is today. Yeah, I think so. And even when we recommend fermented foods, that's with the best intention of saying,

listen, they contain probiotics. They also may be prone to not surviving the hostile environment of your stomach acid. and digestive enzymes, and they might also not take root and colonize, but they're cheaper. It's far more safe in terms of risk profile. There is a chance they can take root, but also more than that, they have a host of other benefits beyond just the probiotic nature. So, you know, yoghuts and kimchi, for example, you're eating it for, you know, the protein or the fiber or the other spices, not just a probiotic value. When you buy a probiotic, there's no other value in the probiotic. There's no extra protein, there's no other vitamins or minerals. It's just a

probiotic. But with food, you get all these other benefits as well. I'll end this recap with something I think you'll like, a free gut health guide created by our team of scientists here at Zoe. Many of us aren't sure how to best support our gut. So we developed an easy-to-follow guide, complete with tips, recipes and shopping lists designed to help you look after your gut. The guide is delivered straight to your inbox, along with ongoing nutrition insights from Zoe, the Science and Nutrition Company on a mission to transform their health of millions. To get your free gut health guide, just visit zoe.com slash gut guide. Thanks for listening.