In short
Gut health recap focused on evidence-based, simple changes—especially feeding the gut microbiome with fiber and diverse plant foods—and skepticism toward probiotic supplements.
Guest background
Dr. Karan Rajan is a clinician who has prescribed medical-grade probiotics in limited situations; he discusses microbiome science and regulation differences between medicines and over-the-counter supplements.
Key claims
Digestion is coordinated by the brain and circadian rhythm; most digestion and microbiome activity occur in the small intestine and colon. Microbiomes respond within 24 hours to diet changes. Fiber/prebiotics act as “fertilizer” for gut bacteria; a target around 30g fiber/day and color variety (polyphenols) support gut health. Probiotic supplements: consumer products are not one-size-fits-all, aren’t rigorously tested, may not contain the right live strains/doses, and could pose risks (e.g., small intestinal bacterial overgrowth, contaminants, possible antibiotic-resistance concerns).
Notable examples
Fermented foods (yogurt/kimchi) may help but for broader reasons than “probiotics” alone. Mentioned Zoe-linked insights: Dr. Will Bulsiewicz suggested yeast in a toe injury scenario; Tim Spector advised fermented foods instead.
Written by AI. May contain mistakes. Listen to the episode to check what was said.
Chapters
Tap a time to open that second in VOUnderstanding Gut Health
0:46 to 1:22
Exploring the importance of gut health and its role in digestion.
“When we talk about the gut, we're not just referring to the stomach, are we?”
Role of the Brain in Digestion
1:23 to 2:26
How the brain influences the digestive process and gut health.
“your head, and all these juices are beginning to, starting to be secreted.”
Food's Impact on Gut Health
2:27 to 3:37
Discussing dietary changes that can positively affect gut health.
“but then I'd love to discuss some of the other things that you talk about as well.”
Nutrients for Gut Health
3:38 to 4:25
Examining the importance of fiber and plant-based foods for gut bacteria.
“but also an abundance of variety as well.”
Feeding Your Microbiome
4:26 to 5:38
Understanding how to nurture the gut microbiome for better health.
“which we can't process to then churn out other beneficial nutrients like vitamin K, B12, and much, much more.”
Probiotics: Pros and Cons
5:39 to 10:07
A critical look at the effectiveness and risks of probiotic supplements.
“And what's interesting is that I've been on a long journey with my own health and my symptoms got much better through my 20s and 30s.”
Fermented Foods vs. Probiotics
10:08 to 12:55
Comparing the benefits of fermented foods to probiotic supplements.
“I think I would, 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 and we have, or even generic probiotics, which actually do work.”
Transcript
Automatic transcript. May contain errors.0:00Hello, 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 favorite 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 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.
0:48Dr. Karan Rajan: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 salivary glands in your head, and all these juices are beginning to, starting to be secreted.
1:32Dr. Karan Rajan: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.
2:06Dr. Karan Rajan: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.
2:41Dr. Karan Rajan: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 changes in the microbiome. So, you know, if you look at most of the, you know, literature that's out there, the meta-analyses 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.
3:16Dr. Karan Rajan: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 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 colors. because the colors are linked to varying levels of polyphenols, which are antioxidants, natural phytonutrients, plant chemicals, which provide this sort of anti-cancer, anti-inflammation effect.
4:02Dr. Karan Rajan: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.
4:42Dr. Karan Rajan: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, colorful foods, diversity, and fiber, those are the kind of very, very basics. And all of that, interestingly, 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 healthy 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?
5:13Dr. Karan Rajan:Yeah, I think, you know, more so than worrying about, you know, adding more good 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 symptoms I have and just really no thinking at all about this idea that you have the microbiome, that you need to feed it.
5:52And what's interesting is that I've been on a long journey with my own health and my symptoms got much better through my 20s and 30s. 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, 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 there are doctors now sort of talking about this.
6:26I do want to ask a bit, because I think you were just switching there to contrast, I think, eating food with probiotic supplements, eating something which says it has bacteria in it. And I want to come back to the question right at the very beginning. What are your thoughts on probiotic supplements?
6:44Dr. Karan Rajan:So I've prescribed probiotics to patients, limited over my career, but these are medical-grade probiotics, have specific strains, 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, antibiotic-associated infections, maybe certain subtypes of IBS, and certain post-bowel cancer or bowel surgery states, they may have some effect.
7:36Dr. Karan Rajan: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? That'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.
8:14Dr. Karan Rajan:They don't have to go through the rigorous medical testing and trial testing. So actually, these probiotic supplements, juices and drinks, don't have to actually back up any evidence that they 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 claritin 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.
8:45Dr. Karan Rajan: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 overcrowd 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? And, you know, what if they contain contaminants? So actually, more so than money, there is published evidence suggesting there could be risk as well.
9:20Dr. Karan Rajan: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 harmful in a way that it contributes to antibiotic resistance. because 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 bacteria which already are inside us, that we host, could increase the risk of antibiotic resistance.
9:58Dr. Karan Rajan: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 would, 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 and we have, or even generic probiotics, which actually do work. But I don't think with 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.
10:33Dr. Karan Rajan: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 that 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 described 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.
11:07And 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 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 Spector and Will Bolzewicz.
11:41And 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 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.
12:12Dr. Karan Rajan: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 acids 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 yogurts and kimchi, for example, you're eating it for the protein or the fiber or the other spices, not just the probiotic value.
12:48Dr. Karan Rajan: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. As you can imagine, hosting this podcast, running Zoe, juggling family life, it all keeps me pretty busy. So I try as best I can to stay energized and show up well in all those parts of my life. by fueling my body with the right food, by exercising, and by adding a scoop of Daily 30 to my meals every day. If you haven't heard of Daily 30 yet, it's the gut supplement designed by our gut health scientists here at Zoe.
13:25It's made of over 30 high quality hand-picked plants, including seaweed, fungi, and different types of fiber. Better yet, it contains ingredients that support gut health, digestion, and energy, which is ideal for packed calendars and busy lives. Simply add one scoop a day to any meal for an extra boost of fiber and plant diversity. And because it tastes delicious on just about anything and adds a satisfying crunch, it quite quickly slots into your life, becoming a daily healthy habit you'll always have time for. By the way, whenever we talk about Daily 30 as a good source of fiber, we're required to say that it contains four grams of total fat per serving.
14:06Obviously, that's all amazing healthy fats from plants. so order yours today at zoe.com daily 30 thanks for listening and see you next time
From the publisher
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 by our ZOE Scientists
The Food For Life Cookbook
Every Body Should Know This by Dr Federica Amati
Food For Life by Prof. Tim Spector
Ferment by Prof. Tim Spector
Free resources from ZOE
Live Healthier: Top 10 Tips From ZOE Science & Nutrition
Gut Guide - For a Healthier Microbiome in Weeks
Better Breakfast Guide
Have feedback or a topic you'd like us to cover? Let us know here
Listen to the full episode here
