How to unlock the secret power of mushrooms to heal your gut, cut cholesterol and protect your brain with Prof. Robin May

Could mushrooms hold the secret to better gut health, lower cholesterol, and can they protect your brain?

Today, Prof. Robin May, a leading microbiologist and the UK Government’s Chief Scientific Advisor, explores why our interest in mushrooms has exploded.

He explains why they are not just another vegetable but could hold the key to better gut health, brain health, immune health, and lower cholesterol.

Should mushrooms become a regular part of your weekly shop rather than an occasional side dish? And if fungi have evolved alongside humans for millions of years, what else might they reveal about the future of nutrition and health?

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Actionable takeaways

Should mushrooms become a regular part of your weekly shop?

Yes — the simplest win is consistency. Treat mushrooms like a regular vegetable to add to your favourite meals. If you can, rotate types for more diversity (e.g., button, oyster, shiitake).

Is it possible to boost the vitamin D content of mushrooms?

Yes! Mushrooms can produce vitamin D when exposed to UV light. Lay mushrooms in direct sunlight for 1–2 hours before eating to significantly boost their vitamin D content.

Do you lose all the benefits of mushrooms during cooking?

No. Cooking doesn’t destroy all the beneficial nutrients, and it can actually be the better choice for safety and digestion. If you boil your mushrooms, use the liquid in your meal, because some nutrients are water-soluble and can leach into the water.

Are mushrooms good for gut and overall health?

Mushrooms contain fibres and complex carbohydrates that can feed beneficial gut microbes. Supporting a healthier gut microbiome may have additional benefits for immune function and inflammation, because the gut microbiome and immune system are closely linked.

Can mushrooms help lower cholesterol?

Potentially. Mushrooms contain beta-glucans, which can form a gel-like substance in the gut that helps bind cholesterol (especially LDL) so more of it leaves the body rather than being absorbed.

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Jonathan: Are mushrooms more closely related to humans than to plants?

Robin: Yes.

Jonathan: Do some mushrooms contain vitamin D?

Robin: Yes.

Jonathan: And finally, what's the biggest myth that you often hear about mushrooms?

Robin: I think it's the weirder the mushroom, the better it is for you. Caution against that one.

Jonathan: Not true?

Robin: No. Stick to the mainstream, I'd say.

Jonathan: Is that only 'cause you might die by eating the weird mushroom, or-

Robin: There's quite a lot of risky, weird mushrooms out there, so yeah, if someone's selling you something in a brown packet, I would be cautious.

Jonathan: When I was young, mushrooms were definitely something I ate, but only because my mom liked the taste of mushrooms and she was cooking. And then more recently, I feel like I'm surrounded by claims that mushrooms can extend your life, like improve your immune system, prevent brain aging, and so on. Now, look, I love the taste of mushrooms, so any excuse to eat mushrooms is good, but my son hates them. So it's not really the taste, he doesn't like the texture. So my objective for this podcast is to come out with compelling arguments for why he should keep eating mushrooms even though he doesn't like them very much.

Robin: Right. Okay. Mission in mind. Yeah, I can't change the sliminess, I think, but bad luck.

Jonathan: You had this crazy answer that a mushroom is more closely related to me than it is to a plant. So what is a mushroom?

Robin: So we now know pretty clearly that mushrooms and animals share a more recent common ancestor than plants do. So if you think about that evolutionary tree of life, plants branched off earlier than fungi generally and animals did. So hence the answer, we're more closely related to a mushroom than to a plant. Not by much, I have to say. That branching is still a very long time ago. But actually that explains quite a lot of things, I think, about mushrooms. So if you think, you know, the most obvious thing is they're not green, right? They don't photosynthesize, plants do. So that tells you already that they're probably not a plant. If you look sort of molecularly, there are quite a lot of other reasons why they are more similar to animals. So, for example, some of the machinery that we use to make proteins in our cells, fungi use a machinery that's more similar to ours than the machinery plants make. So there's quite a lot of reasons to be confident that we are more closely related to fungi.

Jonathan: And so you just started to touch on it, but are there other differences between fungi and plants? And so does that mean that somehow if I was eating a mushroom, there are therefore genuinely gonna be things that I'm sort of eating that wouldn't be in a plant?

Robin: Yeah, absolutely. Yeah. So perhaps the most obvious is that plants and fungi both have cell walls, which is why they're rigid, unlike animal cells, we're pretty floppy, but it's made of something completely different. So plants are made of cellulose. People might remember that from school. Fungal cell walls are made of a molecule called chitin, which is actually the same molecule that is in the shell of crustaceans, so lobsters or crabs or insects. They're the crunchy bit. If you step on a bee and it goes crunch, that is chitin. It's the same molecule in a fungal cell wall. So that's a really obvious one. And then if you kind of really look biochemically, I mean, one of the most amazing things about fungi is they are incredibly chemically diverse. And so for instance, many of the antibiotics we get today are produced by fungi because they're able to do this fantastic chemistry. In some cases, chemistry that we haven't managed to crack as humans yet. So there are, depending on the species, lots of molecules you find in fungi that are not found in plants or in animals or sometimes even in other species, sometimes really unique.

Jonathan: And so that means that if I was eating a mushroom, there could genuinely be, like, molecules in there that I just would never get even from eating lots of diverse plants?

Robin: Yeah, absolutely, and they can be good, bad, or indifferent. So there are some nutrients that come from mushrooms that are really important. But of course, people are familiar with the fact that some mushrooms, some toadstools, are hugely poisonous, potentially lethal, and of course, there are also magic mushrooms that produce hallucinogenic compounds that are not found in other species.

Jonathan: Now, I asked about mushrooms and you immediately switched out to fungi. I ran with it, but can you help me to understand what the difference is?

Robin: Yeah, absolutely. So we talk about the fungal kingdom. So if you think about, we talk about plants and animals and fungi, so each of those is a kingdom, is a big group, and fungi as a kingdom, we don't really know how big that is. We estimate probably something like one and a half million species, of which the vast majority are still not known to science. They are all closely related in the sense that they all share those characteristics like a chitin cell wall, but they are wildly different. So for instance, athlete's foot on your foot is a fungus. The yeast that you put in to make your bread rise or your beer brew is a fungus. The mushroom you buy in your supermarket is also a fungus. So fungus is the wider group. Mushroom sort of doesn't really have a kind of biologically defined term, but we tend to use it for the fruiting body. So if you think about what a mushroom looks like in a supermarket, if you see that growing in the field, that's actually a tiny fraction of the whole organism. Most of that organism is invisible underground in this kind of hair-like network that's called a mycelium, but it's only when it fruits that comes up. So I guess it's a little bit like thinking about, you know, we talk about an apple, but the apple tree is, you know, much bigger than the apple alone. So the mushroom is the fruiting body of a particular species, and not all fungi produce mushrooms. So the yeast that you make bread with, you know, you don't come-- hopefully you don't come down in the morning and find mushrooms popping out of your bread. Certainly not from that yeast anyway. It stays as a yeast its whole life. Other fungal species can move between this yeast form and this kind of fruiting form. Actually, the kind of scale of the invisible part of fungi is something people often overlook. So if you think about out in your garden or the woods, you know, you see a toadstool pop up. Often that toadstool is revealing the presence of a mycelium that's enormous. And in fact, there's quite well-documented cases in the United States, for example, of individual fungi that stretch for miles underground. So you see a mushroom pop up here and five miles down the road you see another mushroom pop up, and it's actually fruiting bodies of the same super organism that's under your soil, but we just can't see that bit.

Jonathan: That's wild. So you're saying there is just one fungi that can be, like, five miles long?

Robin: Yeah. Biologists like to fight over kind of records and if you're a kind of mycologist or someone who specializes in fungi, you always claim that you have the biggest organism in the world because if you were able to haul that out of the ground, it would be far larger than a blue whale or a giant redwood. Obviously, the problem is we can't actually extract it and show that.

Jonathan: Now, I think all our American listeners will say, "Yeah, but of course everything's bigger in America." So is it just in America that you get five-mile fungi or if you were in Europe or Australia, whatever, I mean, is that also true?

Robin: Yeah, I feel like we might be starting some kind of international competition here for large fungi. No, so the largest one that we currently know of is in the United States. I don't think there's any reason to believe it would have to be in the United States. I suspect quite a lot of this is about who's going looking. You know, there are lots of really great mycologists in the US who look at these things, but I'd wager you can find a bigger one in Brazil if you go looking.

Jonathan: When I was young, like, I only ever saw button mushrooms in the store, and now I regularly see, like, oyster mushrooms and shiitake and lion's mane, and that obviously represents the fact that many more people are eating mushrooms, and also, like this sort of wilder diversity. What's been driving that shift in terms of just, like, what we're able to eat in the supermarket?

Robin: Yeah. I think there's probably a couple of things that are playing there. So I mean, obviously, here in Europe and the US, we've been very restricted in our palates for quite a long time. I mean, that's not true in the Far East, for example. I well remember many years ago traveling to Japan, you know, and having just extraordinary dishes with mushrooms, which I had never seen before, and which people couldn't tell me the name of. So I think many cultures have a much more diverse repertoire already. Part of that change in Europe and the US in recent years has been that globalization of the food economy, people traveling, eating stuff they like elsewhere and saying, "Why can't I buy it here?" Partly it's also about the ability to produce these. So producing mushrooms or related fungi is quite different to other sorts of farming. And so it takes investment, it takes kind of skill, and so you have to sort of have a market that's gonna make it worthwhile. But of course, as we know, the more exotic fungi, mushrooms often sell for quite a premium, and so there's been quite a big market driver to support the development of those. And I think probably the last thing is that people have become sort of more experimental in their diets. People are very interested in healthier diets, more diverse diets, cuisines from elsewhere, and so I think it's driving that overall kind of shift in what we buy and what we cook.

Jonathan: I'm struck by you saying that when you first went to Japan, you suddenly saw that they ate all of these different mushrooms and you're an expert, but you're like, "Oh, I don't even know what this mushroom is." Is that because there just were many more varieties of mushrooms that you can eat? Or is this just because somehow Western Europe and obviously, you know, places like America just were not really open-minded about it?

Robin: Yeah. I think it's probably a bit of both. I think, I mean, so one of the characteristics of most fungi like growing in kind of damp, humid conditions. I think there's something about the climate you're in. So if you take the UK, for example, you know, middle of winter you can't go and find mushrooms out in the wild because it's too cold and there's just not enough environment for them. If you're in the tropics, you can find mushrooms, toadstools all year round. So there's something about availability historically. But I think there's also something about sort of cultural acceptability, and particularly the kind of flavors. A lot of fungal species that we eat, especially the more unusual ones, have really quite marked flavors, and we know that people are usually quite reluctant to kind of experience new flavors initially, and they have to kind of be exposed to it. And so one of the things, for example, is that many fungal species have a very strong, you know, umami flavor. This sort of... It's quite difficult to describe, as it's kind of rich, kind of deep flavor that polarizes people. I think that's a much more common flavor historically in Asian cuisine, for example. And so people are ready to embrace this. I suspect in 1950s England, if you'd have come with a strong umami flavor, people might have, you know, run away.

Jonathan: I'd love to now sort of almost drill down to nutritionally speaking, sort of what's in a mushroom.

Robin: Well, it depends first of all on what we mean by mushroom, I think. I mean, clearly the one we know the best is the classical mushroom that you buy from, you know, the supermarkets, white or brown, big cap on the top. It's an Agaricus species, and we know quite a lot about that. Mushrooms are often used to replace meat in sort of vegetarian-type cuisine. And it's a good replacement. So they have more fiber definitely than animal products. Not as much as some of the kind of really fibrous sort of whole grain food. I wouldn't recommend substituting your granary bread or your oatmeal with fungi, but they are quite healthy in terms of fiber. Good levels of protein. Very low levels of fat, particularly saturated fat. So that's already promising. But the thing that gets people quite broadly excited, I think, about mushrooms is a lot of the more interesting kind of trace elements and vitamins. So if you think about the way that fungi grow, we talked earlier about this kind of, you know, mycelium network in the soil. So they are scavengers, essentially. They're harvesting nutrients from the soil, from decaying matter. So they are really good at accumulating things that are quite rare or trace elements in nature. So for instance, things like potassium, they accumulate very well from soil. Relatively rare compounds like selenium are also quite often accumulated by mushrooms. And then last of all, they're pretty good at making vitamins. So they make vitamin B, vitamin C, and the one that gets people really excited is vitamin D because vitamin D is extremely rare in plant species, and we need relatively good levels of vitamin D, particularly for our immune systems. And so people often talk about mushrooms being a great source of vitamin D, although it is slightly more complicated than that.

Jonathan: I asked at the beginning, is it true that mushrooms contain vitamin D? And I think we often think about that as something you get by being in the sun. What is the reality?

Robin: Yeah. So you're right. So we make it by being in the sun. And just as a kind of caveat here, that does not mean going out and getting yourself lobster pink. That's a very bad thing to do. You don't actually need very much sunshine, even in rainy old Britain. But you do need a bit of sunshine to make vitamin D. Dietarily, we get it from a variety of foods, but many foods do not have vitamin D, and actually mushrooms are a great source. In the winter, in particular, it's quite difficult for people in northerly climes like the UK, or Northern US to make enough vitamin D, so that diet becomes really important. And mushrooms are often touted as a great way to get vitamin D because they make vitamin D, sometimes to very high levels. There are two caveats there, though. The first is that the amount of vitamin D they make is very variable between species. So for instance, if you think about oyster mushrooms, which you can now buy in most supermarkets, they actually on average make about 100 times more vitamin D than your routine field mushroom that might be next to it in the shelf. So there's quite a big variety between mushrooms.

Jonathan: And Robin, when you say routine field mushroom, this is like what I think of, like a little cap. Yeah. And it doesn't matter whether it's white or brown.

Robin: Yeah. Button mushrooms, field mushrooms, the kind you might have on your English breakfast or mushrooms on toast or whatever, that one. So they do produce vitamin D, but they produce less.

Jonathan: And so you said oyster mushrooms create 100 times more vitamin D than, like, the typical mushroom that I grew up with and that I thought was the only mushroom probably when I was 15.

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Robin: Pretty much, yeah. Exactly. And that's very ... You know, different species make more or less. But the big thing about all mushrooms pretty much is they are making vitamin D just like us in response to sunlight, or actually in response to UV light. So if you have-- And of course, if you think about the way mushrooms grow, they shouldn't see very much UV because most mushrooms grow in the dark. So if you grow your mushrooms in a industrial farm in the dark- harvest, stick them on a supermarket shelf and someone comes five minutes later and buys them, they'll have almost no vitamin D in them because they won't have seen much sunshine. But the longer they see UV light for, the more vitamin D they make. And so you might be able to, you know, you might have seen in shops vitamin D-enriched mushrooms, which are essentially mushrooms that have been left in the sunshine for a little bit of time. You can do the same trick actually at home because they will produce that. That reaction to create vitamin D is a spontaneous chemical reaction. So what's happening is a molecule in the membrane of the fungus, called ergosterol, is being converted by UV into vitamin D, essentially. So you don't need the mushroom to be growing to make vitamin D. So actually laying out your mushrooms in a bit of sunshine where it'll get UV, so not inside a glass thing because glass filters out UV, but outside on your picnic table or whatever, they'll start producing vitamin D and actually an hour or two of sunshine is enough to raise the level of vitamin D in mushrooms very dramatically to the point at which a kind of decent serving of mushrooms, eight or nine mushrooms, will give you your daily requirement.

Jonathan: I guess a bit like fruit that continues to ripen and the bananas that I'm used to. You're saying if I put that out in the sunshine for, like, literally one to two hours, suddenly it creates this, like, rather amazing amount of vitamin D. 'Cause you then said, well, then eat eight to nine mushrooms and I've had my daily amount. And if I think about other vitamins, I'm always struck that often they, you know, they claim it's on the pack, but you have to eat an awful lot to actually get the amount that is recommended.

Robin: Yeah, exactly. So, and it's obviously there's a variable art here, not least because mushrooms vary in size. But you know, as a very ballpark sort of estimate, you know, 50 to 100 grams of mushrooms that have been in the sunshine for an hour or two will give you plenty of vitamin D for a day.

Jonathan: Now, you mentioned before that different mushrooms are very different in the amount of vitamin D. So is it all about the oyster mushroom now?

Robin: No, not necessarily. So as you can imagine, not that many mushrooms have been studied. There was an interesting study a few years ago looking at the quantity of vitamin D in various commercial mushrooms. I think the winner actually was the bolete, which is a kind of slightly exotic fancy mushroom that not many people have eaten. So, harder to buy that one from your supermarket. But if you get the chance, they have, you know, I think that's 500 times as much as your typical button or field mushroom. And then oyster mushroom, and then you have, you know, the kinda more routine mushrooms have a bit less. I mean, pretty much all mushrooms do make some vitamin D. So this is, you know, so I wouldn't kind of run away and not eat a mushroom anymore, but it's just worth bearing in mind, especially if you have the opportunity, you know, whilst you're cooking, put your mushroom pot outside for half an hour and then throw it in your omelet and you'll do yourself some good.

Jonathan: And so are the other ones all roughly similar to the button mushroom or is it particularly bad? I'm just curious.

Robin: No, it's not particularly bad. There were, yeah, there were several with that, those kind of levels and actually there's quite a lot of variability there. So one of the things that's slightly frustrating for us scientists is the structure of the mushroom seems to make quite a difference. So you have more of the molecule that turns into vitamin D in some parts of the mushroom. So whether it's kind of flat or open or button makes quite a big difference. Generally speaking, there seems to be more ergosterol and therefore more vitamin D made in the gills, so in the kind of fluffy bit under the mushroom, than elsewhere. But I mean, I wouldn't, you know, I wouldn't take the effort to turn all your mushrooms upside down to make it work perfectly.

Jonathan: And for those of us living in cold northerly climates, is this gonna work or is this a great trick but it only really works in Florida, and frankly they don't need to worry about the mushrooms 'cause it's sunny?

Robin: So you need the UV to make the conversion work, but actually even winter sunshine has a reasonable amount of UVs. If you think about, you know, one of those gloriously winter crisp days in Boston, for instance, you know, putting your mushrooms out will be fine actually, will do quite a good job there. And I think the other point is that this is not your, for most of us, this is not your sole source of vitamin D. So for example, things like cow's milk also have vitamin D. So if you're, you know, having milk on your breakfast and a mushroom, you know, you're still doing pretty well. So yeah, I wouldn't worry too much about that. I mean, clearly if you live in sort of northern Sweden, and you've got 23 hours of darkness, it's not gonna be such a great trick for you in the winter. You might want to think about vitamin D supplements instead then.

Jonathan: Brilliant. Well, I'm definitely now pushing oyster mushrooms right up in my head as I'm thinking about this. While we're talking about vitamins, the team who were doing the research here said that there's a compound that I have never heard of before that I have to make sure I ask you about, which is called ergothioneine.

Robin: Very good. Yeah.

Jonathan: What is that, and why is it that some scientists are apparently saying it should potentially be classified as a vitamin?

Robin: Ergothioneine is a very interesting molecule. It's a natural amino acid, so people might be familiar with the idea that amino acids are the building blocks of proteins. We as humans make about 20, or use about 20 amino acids to build our proteins, but there are other amino acids that we don't make, we don't use, that are used in other organisms, and ergothioneine is one of those. So it's made by fungi in particular, and in laboratory studies it has quite potent antioxidant, anti-inflammatory effects. So antioxidant people might be familiar with this idea of reactive oxygen species. So we're familiar with oxygen that we're breathing now. There is a chemically related molecule, which is a kind of charged reactive breakdown product of oxygen that damages things. It damages proteins, it damages DNA, and it is thought that reactive oxygen accounts for quite a lot of cellular damage as we age in particular. It's one of the reasons, for instance, why, you know, if you spend a lot of time in sunshine you get older looking skin because the reactive oxygen that's created is damaging your cells. So reactive oxygen, not great. Ways to mop up and dispose of reactive oxygen are therefore thought to be beneficial in protecting us from damage and helping delay aging. And ergothioneine is a really good molecule at mopping up oxidative damaging agents. So in a lab, absolutely this soaks up reactive oxygen, so that seems like something you might want in your cells. And so there has been quite a big kind of interest in whether eating loads of mushrooms will give you lots of ergothioneine, and that will help protect you. Have to say the data on this is very much still up for debate. So, if people are listening to this, I wouldn't race out and order yourself massive supplements. We're still a long way off being sure. What we do know is that in some situations it does seem to have some potential beneficial effects. There have been some studies looking at cellular hallmarks of aging, and if you're exposed to ergothioneine, it seems to reduce that. No really good clinical data suggesting broader health impacts than in it, but as with all science, you know, there's a lot more to do in this space. One of the really big mysteries, I think, to ergothioneine is we humans have a specific protein that is used to take ergothioneine into our cells. It's very conserved, so other species have this too, and that sort of suggests that it must do something really quite important because evolution has kept it and looks after it. However, our kind of typical way of testing these things is to remove it genetically from mice, for example, for instance. Those mice seem pretty fine actually. So there's a bit of an enigma here that we have this protein that appears to have been conserved, does something important, but we don't know what the important thing is. And perhaps the last and most weird unexplained thing is that that version of that protein that takes up ergothioneine varies between different humans. So different populations have what's called polymorphisms, variation of this. We don't really know what that means or why that's important, but there has been quite a lot of renewed interest in that because it looks like one particular variant of this is associated, and I stress associated rather than causative, but associated with Crohn's disease. And so if you carry that particular type of ergothioneine receptor, you appear to be more at risk of Crohn's disease. We don't know why, and it may be complete, you know, red herring or correlation. But yeah, a lot of interest in ergothioneine.

Jonathan: So this is one of these examples where we're getting access to, like, this very early scientific insight, but you're not suggesting that we all have to go out and make sure that we're getting enough ergothioneine from our mushrooms and we're all going to live another five years of healthy life.

Robin: Yeah. I mean, it's kinda like the scientific equivalent of that moment when you've finished your flat pack furniture and you've got this thing left over and you think, "This looks like it does something really important, but I don't know where it goes." And so we're at that point, I would say.

Jonathan: Do all mushrooms have, like, high levels of this ergothioneine or is this only in particular mushrooms?

Robin: So not all mushrooms produce ergothioneine, but it is relatively widespread. So it's very rare in other branches of life. So plants don't make it, animals don't make it. The places it's made naturally are quite a lot of fungal species and in the cyanobacteria, so these photosynthetic bacteria that are associated with things like algal blooms in the sea, but obviously we don't eat those. So mushrooms are your best bet. Levels vary in different mushrooms, and we don't really know how they vary in different species. We also don't actually know what a sensible level would be. So although it has neuroprotective effects, you know, because we don't know what it does, we don't know whether you... There's a thing, such a thing as too much of it or too little, so.

Jonathan: So if I was having like a standard like button mushroom, is there likely to be some ergothioneine in it?

Robin: Yeah, there is. Your standard mushrooms have some, levels vary. And again, we don't really know what a good level is. So, I mean, no evidence of harm, so that's always a positive thing. But I think we're, yeah, we're definitely far from saying this is some kind of magical cure all.

Jonathan: And so we talked about vitamin D, we talked about this ergothioneine. You mentioned at the beginning that there's quite a lot of fiber in these mushrooms.

Robin: Mm-hmm.

Jonathan: Are there any other nutrients that are, like, helpful for us that are in mushrooms?

Robin: Yes. So most mushrooms produce vitamin B and vitamin C. And they also, I think we mentioned earlier, they harvest these kind of minerals like potassium and selenium. And they do quite a good job of that actually. So generally there's quite a lot of kind of trace elements or minerals that are in mushrooms that are good for you.

Jonathan: I'd love to talk now about some of the health claims that surround mushrooms. So less about the nutrients and more like what does this actually mean for us as human beings? And I know talking to friends of mine from like China and Japan, that apparently they've been like an important part of their sort of traditional medicine apparently for thousands of years. But I'd really like to know what the science says. Is there any evidence that's suggesting eating mushrooms is linked to either healthier lives or longer lives?

Robin: Let's focus first of all on kind of your classical supermarket mushroom. And the short answer is no, not really. So there have been a couple of studies looking at these very large population studies looking at diet and longevity. Couple of caveats. One is they're usually done by what's called recall studies. So people say, "Jonathan, what did you eat last Tuesday?" You know, and I don't know about you, but often I think, "I don't know what I ate last Tuesday." So there's a lot of patchiness in the data. As part of a broad, varied diet that doesn't have too much red meat, et cetera, they do have a significant benefit. So for example, even if the mushroom on its own is not particularly dramatic, if you're replacing your fillet steak with a, you know, mushroom, then actually that will have a benefit because we know that too much red meat is bad for you. So there's a thing about eating mushrooms as part of a varied diet that's good, but as a kind of magical food to make you live forever, unlikely, I think.

Jonathan: So is it just that the data isn't there and you think it is beneficial for health, or do you think that it's like a good thing, like lots of different plants are, but, you know, even if we did a great experiment, you're not gonna see any impact?

Robin: I think the data is a real challenge for a couple of reasons. So one is that we talk about mushrooms in inverted commas, but you know, that's a bit like talking about plants, you know? And if I was saying to you, you know, does eating plants correlate with long life? Well, yes, it definitely does. If you don't eat any plants, you're not gonna live very long. So I think there's a big problem there that we talk about kind of mushrooms generally, and we're not able to distill in to individual levels of detail. Secondly, of course, it's actually pretty recent. I mean, in some cultures people have been eating mushrooms for a long time. In most Western European, US, cultures, it's a very small number of species for a very short period of time. And those are the areas of course, where most of these long studies have been done. So the data is not just the data is not there, but the experience of people is not there to draw on. That might change going forwards now that people eat more species. There is the potential to really look in more detail, particularly in other cultures where, you know, a broader diversity of fungi have been eaten for a longer period of time and maybe we'll see something interesting then.

Jonathan: One of the big things I hear is about brain aging. Is there any evidence around this or any reason to think even that it might matter?

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Robin: Yeah. One of the points about fungi is that this is a huge, diverse group of organisms, right? One and a half million species, and they are amazing chemists, so they can produce just wild molecules. And you know, perhaps the best example is, you know, antibiotics, right? Penicillin is a fungal product. I mean, now we make it synthetically, but it was a fungal product and so they can make incredibly impressive chemicals. So, you know, at face value might mushrooms in inverted commas help us live forever? Absolutely. 'Cause somewhere out there might be a species making something really important. If we're thinking about kind of the small number that we eat at the moment in its part of regular diets, there's been quite a lot of interest in whether particular species might help protect your brain. And lion's mane is the one that's often quoted as a kind of, you know, lion's mane fungus, live forever. And there is a little bit of data suggesting that it's worth at least looking at this in more detail. So for example, some extracts of lion's mane and actually some other species seem to, in a laboratory setting in a dish, stimulate nerve growth. And so the, you know, at face value you might say, well, creating a few more neurons if you're, especially if you're losing neurons due to, you know, dementia or something else might not be a bad thing. So there's a kind of plausible biological mechanism. In terms of kind of studies in people, the jury is very much out. So there have been some studies demonstrating slight improvement or a slowing in reduction of brain capability in people with early mild cognitive decline. Small studies, not highly replicated yet, so, you know, be cautious, but perhaps slightly promising. There was one interesting study that people often talk about a lot on social media where people without any cognitive decline, relatively young people, showed an improvement in their mental score on a kind of classical test. Which actually is a test where it's very rare to see things that improve that score in people who don't have cognitive decline. So you might see online people say, "Wow, your IQ will go up if you eat this." Which is based on those kind of studies. Again, very small, very limited. There has been at least one study which has shown the opposite, which has shown if you have it, your ability to recall words drops. And so like much of science, I think we are still a long way from a kind of solid answer.

Jonathan: And so when you look at all of that, you know, I think a lot of what you're taught, right, is to discern the different quality of evidence across these studies. What's your guess about mushrooms and their ability to have any impact here?

Robin: Yeah, I think I would happily wager a mortgage payment on the fact that somewhere out there in the fungal kingdom, there will be, you know, fungal products that are gonna be massively beneficial for medicine and therefore longevity. And I wouldn't rule out the possibility that, you know, in the future there will be particular species or particular extracts that will be recommended for everybody to take. If you enjoy it, it fits in with your lifestyle. There's no evidence of harm, but I definitely wouldn't, you know, go out of your way to take a particular mushroom supplement in the hope that it will help you live forever.

Jonathan: The other, I think, big area that I read a lot of claims is around immune health and inflammation. Like, we've seen more and more this overlap between that and the microbiome. So I think most of our listeners are sort of aware that long-term inflammation is not something you want to have, but we all have this, like, high level of long-term inflammation living in the Western world compared to the past. Is there any evidence that eating mushrooms can have any beneficial impact there?

Robin: So I think it's really important to think about, again, about this kind of breadth of the fungal kingdom here. And, you know, because I spent quite a lot of my life working on fungal diseases that kill people, I do wanna kind of emphasize the fact there is a spectrum here, right? There are fungal species that are probably very good for us and we eat. There are fungal species that, you know, you really don't wanna get.

Jonathan: This is your, "I have athlete's foot," but even though it is a fungus it's not a good thing. I was thinking to say 'yes'.

Robin: Exactly. Athlete's foot, definitely not great, although that's more in the annoyance. But there are, you know, a handful of fungal species that are potentially fatal, particularly for people who have weakened immune systems. I think really important to stress here that, you know, if you are thinking about, "How can I prop up my immune system because it's already impaired, I've got a genetic disorder or I've got HIV positive or something," you know, dietarily, absolutely fine, but if you read someone's magical thing about sniffing a fungal spore, just don't do that. But that notwithstanding, I think one of the interesting things about fungi generally is that many of the molecules that are present in fungus, particularly on the surface, do have quite potent immune effects in humans and other animals. That's largely, I have to say, because the immune system has evolved to react to and get rid of fungi. It's not a good thing to have fungi growing in your lungs, for instance. If you think about that cell wall of the fungus, most fungal species have a molecule called beta-glucan inside that fungal cell wall. That's a really potent immune stimulus. So if you put beta-glucan into somebody, their immune system lights up because it's trained to say, "Here's something I should react to and get rid of it." And in fact, we use beta-glucan as what's called an adjuvant to help some vaccines really generate a good immune response. And so there are definitely immune effects in fungi. Less clear is the kind of ability of the immune system of fungi to suppress the immune system. So there are specific examples, particularly in some pathogenic fungi, of molecules that the fungi use to deliberately suppress the human immune system, but that's for their own advantage, right? That's 'cause they want to grow. And so I definitely wouldn't recommend people expose themselves to those two. Unclear at the moment whether similar molecules in fungi that are not harmful might be beneficial. So yeah, sort of jury's still out. Probably the last thing to say on that, though, is there's also a sort of secondary effect in that fungal products are really important for influencing the microbiome of the gut. So for example, many of the sugars and the carbohydrates that fungi make are really good kind of food stuffs for the bacteria in your gut. And so there has been quite a bit of evidence that some mushroom species will help stimulate a kind of good microbiome, for want of a better word. And of course, the good microbiome can have a very strong positive effect on your immune system.

Jonathan: So it's interesting you're wrapping up on a topic that obviously we love on this show, and you're saying that perhaps one of the most valuable things that these mushrooms are doing is actually to be food for our gut microbes, and they might then be producing these compounds that are beneficial for us.

Robin: Exactly. Exactly.

Jonathan: This is a lot like a plant where, again, there's lots of things here that I can't digest directly, and so if I want to get the benefit, I need to get the microbes to sort of break it down for me.

Robin: Yeah, exactly. So there's, you know... And we often sort of overlook, I think, the fact that your microbiome is just this wildly complicated ecosystem. And if you think about the relationship, bacteria and fungal species have been evolving together for, you know, obviously far, far longer than we have. And so there are some really quite complicated signals. So if you look, for instance, out in soil, you know, there are really well-documented situations where the bacteria might make a molecule, the fungus picks it up and behaves differently. It produces a different molecule. The bacteria changes its behavior. There's a complicated conversation going on. We're only just starting to scratch the surface of that, but very reasonable, I think, to think that when you eat a mushroom, you're probably plugging into that evolutionary conserved kind of communication system and having an impact on the bacteria that live in your gut.

Jonathan: Are there any funguses that should be growing in my gut, or is it now clear that like bacteria are great? But that's again one of these big distinctions. We don't want any of these fungi, and therefore our immune system does not play nicely with them.

Robin: That's a really good and very live kind of topic and, you know, if you go into social media, lots of people with strong views there. Historically, you're right. So people have historically sort of said fungi growing in your gut, bad thing, and in some circumstances that is definitely true. Like most things about the gut microbiome, you don't want dominance of a particular species, for instance. That said, it's really only in recent years that we've started to understand a bit more about what appears to be the kind of natural fungal microbiome of the gut, and that's largely speaking because they are massively outnumbered by the bacteria. So early genetic sequencing, you know, you just take your abundant DNA, and it's only with the advent of technologies which allow us to look at very rare, very low levels DNA that we start to see these fungal species. And I think kind of an emerging view that there are definitely some species that are probably quite good to have in your gut. Still very unclear which ones those are and what they might make the difference for them. But I think that sort of realization that fungi are kind of everywhere and are part of your natural microbiome, very important. And in fact, you know, outside of the gut, so skin for example, you know, we're covered in interesting fungi that do all sorts of weird, wonderful things. My favorite example being this one called Malassezia that grows only really on the human head, and in fact, is only able to reproduce in the presence of human sweat excretions. So there you go.

Jonathan: You're now kidding me.

Robin: Nope. There is a fabulous demonstration that this particular fungus is completely required. So I have a colleague who says it's a creepy feeling to think that there's a endangered species that can only have sex on your head.

Jonathan: There is a fungus that can only grow on the human head and cannot reproduce unless it gets the particular, like, sweat that comes off from the human head.

Robin: Yeah. It's the oils that you produce in your head that seem to be a signal for it to sporulate, so to produce reproductive organs.

Jonathan: That's fascinating. This is this example of how we are this ecosystem with these tiny microbes, and that includes fungi. We talked about bacteria a lot, but you're saying there's fungi that absolutely only coexist with us.

Robin: Yep.

Jonathan: You know, you might think that's just a parasite, but is your view that on the skin some of these fungi are actually beneficial to us?

Robin: Yeah, absolutely, in two different ways. So there are probably some species that are genuine sort of symbionts. So they're there, they never do any harm, and they're kind of good for, you know, whatever reason. They might be helping to sort of digest things you don't want, or they might be kind of helping to regulate the immune system. But also there are species that are sort of at face value potentially bad news, but their presence helps with this kind of maintaining a normal immune system. So one that's often talked about is Candida. And there's a sort of whole world out there of kind of Candida syndrome and Candida things. So Candida is absolutely a fungal pathogen that can cause serious disease. It can cause, you know, vaginal thrush, oral thrush, sometimes systemic lethal fungal infections. But all of us have Candida all the time. If I'm gonna go and swab my armpit, you'd find Candida there, and that's not a bad thing. It's there, it's kept in check by the immune system, and it's probably helping to keep our immune system in balance. So, you know, as with many of these things, you don't actually want to be a sterile site. It's good to have a healthy microbiome, even if it includes things that can on occasion go bad.

Jonathan: Absolutely fascinating. I also heard that mushrooms might have a cholesterol-lowering compound. Is that true?

Robin: That is true. So they produce in their cell wall this molecule that we mentioned earlier, beta-glucan. So the main structural component of the cell wall is chitin, that thing that's in lobsters and beetles and things. But they also have this layer called beta-glucan, and beta-glucan is a polymer, so it's a chain of sugar molecules, glucose molecules. We talk about beta-glucan, but actually this is a whole family of molecules, 'cause if you think about joining your sugar molecules together, you can put branches on them, you can do different things. So their structures are all quite different. However, what appears to be pretty clear now is that when we eat beta-glucan, it can kind of form a sort of gel in our guts, and that gel is actually very effective at absorbing cholesterol, keeping it away from your cells, especially LDL, so the kind of bad cholesterol, and then essentially getting pooped out the other end without you taking up too much. So this is the same group of molecules that is what makes oats really good for you. So our, you know, recommendation to eat oats, oats are great at helping to lower cholesterol. Fungi produce less beta-glucan than you have in oats, but nonetheless quite a significant amount. So if you're already having oat porridge, great. I wouldn't swap that out for a mushroom in the morning. But if you're taking mushrooms additionally, it's another good way to help lower cholesterol.

Jonathan: I would like to talk about actionable advice about, like, how can I actually add mushrooms successfully into my diet. Could we talk about the cooking for a minute? 'Cause I always feel that when I cook mushrooms, it feels like the darn things basically disappear, right? They're really big, you cook it on some heat, and it just, like, shrinks and shrinks. And so I've always sort of felt, well, I've probably killed everything that is of any value 'cause it all shrunk away. Is this right?

Robin: Not necessarily. So heat does remove, particularly vitamins, you know, levels of vitamins drop quite dramatically when you heat, especially for long periods of time. Um, having said that, of course, depending on what you're doing with your mushroom, you might not be heating for very long. So if you're kind of frying a mushroom, you know, if you think about one of those big, fat, delicious field mushrooms, you know, you might give it a minute on one side and 30 seconds on the other, and you're done. So actually in that sense, you're retaining kind of more vitamin than if you're gonna put it in the oven for an hour. Probably the bigger risk with boiling is the water solubility. So a lot of these things that are in mushrooms are highly water-soluble, so vitamins B and C, but also things like potassium, are very water-soluble. So if you're gonna boil your mushrooms and then just throw away the thing they were boiled in, that is leaching out quite a lot of your nutrients. If, clearly, if you're boiling it in a pasta sauce and you're gonna eat your pasta sauce, not a problem. You've just moved your potassium from inside the mushroom to outside.

Jonathan: And a bit like thinking how I was brought up to do carrots, you know, if you put it in a great big pot of water, and then you throw away the water, it's like literally you're throwing away-

Robin: The good stuff.

Jonathan: the good stuff.

Robin: Yeah, exactly. I mean, my usual, you know, best rule is the best way to cook something is the way that you're gonna eat it. You know, so if you're someone who will only eat a mushroom if it's been cooked for a long time, then that's fine, because the alternative is not to eat it at all.

Jonathan: What about preparing the mushrooms? One thing I'm always struck by, as a mushroom comes, it always feels like it has, like, dirt and mud on it. I always feel like, well, I gotta, like, sort of scrub the dirt off it. It also puts me off a bit eating it.

Robin: You know, back in the old days, you'd say, "Oh, you should peel your mushrooms." Actually, you know, that's a relatively... If you're worried about the dirt component, there's a relatively limited value in peeling, because as we know, the bottom bit doesn't have a skin on to peel anyway, and the stalk doesn't and so on, so you're still, you know, you're not removing that much dirt. So I wouldn't worry about peeling. For sort of aesthetic and general kind of taste reasons, it's a good idea to give them a polish off or a wash off, something to get rid of, you know, any soil that's left on them. The world of raw mushrooms, I think, is one that we gotta be slightly cautious about, because like any raw food, there will be other organisms present there, bacteria, viruses, whatever. And so they are potentially a risk. Because of the way mushrooms grow, and the fact they're quite difficult to clean well, that is potentially slightly higher than with other foods. So if you think about, you know, an apple, for instance, you know, it's relatively easy to clean the surface of an apple in a way that you can't do with a mushroom. If you're picking a mushroom straight from the field, you know, you've got no control over what's on that mushroom. And so as with all foods, the risk of, you know, potential food poisoning is higher. You know, I might caution against eating that one raw. The last thing to say is there are some compounds in many fungal species, including fungi that we eat, which can be slightly harmful. I want to kind of caution here, but there's a kind of level thing, but there are molecules called hydrazine, for example, that in laboratory studies appear to be damaging for DNA, so they're potential carcinogens, cancer causes. They're at pretty low levels, so this is definitely not a reason to not eat mushrooms, but they are also broken down rapidly by heating. So if you're someone who's really wild about mushrooms and eats a lot of mushrooms, eating a really large level of mushrooms raw is maybe not a great idea, and I might be tempted to cook them a bit more, partly for the food poisoning reason and partly for this question of residual damaging agents.

Jonathan: My takeaway from this is I probably don't need to worry about the dirt as much if I'm going to cook it, and so I can probably be a bit more relaxed and not let my OCD loose on the mushroom.

Robin: Yeah, I think if you can get over the psychological barrier of eating a bit of sterilized horse manure with your pasta sauce, you're fine.

Jonathan: Would've been easier if you hadn't put it that way. What about- how to cook mushrooms in a way that actually just, like, maximises the pleasure and taste?

Robin: It's very difficult to eat something that's good for you but you really dislike. So I would encourage people to kind of go out and try different mushrooms, because there's lots out there, and they're all very variable. Loads of people, I think, like you said, your son and my son also really dislike mushrooms when they're young because of the kind of slimy texture. Quite a lot of people actually get over that when they're adults, but they often don't know. So I think if you're listening to this and you're an adult and you think, "Well, I don't like mushrooms, but I haven't tried them for 10 years," give it another whirl because maybe they're not as bad as you remember. This is a hugely diverse kingdom, so we have to think about this not as mushrooms, but as vegetables in the same way that, you know, a courgette is not the same as a sweetcorn. And so I think testing different ways, using them in different kind of settings is a really good thing to do. Think about the way of cooking it. So some mushrooms become much more edible, you know, when you fry them. Some become quite tough and stringy. Some are great when they're ground and powdered. Some just taste like dust. And so there's a sort of sense of the diversity of mushrooms out there, and also the kind of way you're preparing them. And last thing I think is think about the kind of meal you're using them in, and the strength of, you know, experience. So I, you know, think there are a lot of people out there, for example, who've had a very bad experience with truffles, 'cause they get this thing that looks absolutely tiny and think, "Oh, I'll chop that up and throw the whole thing in." And then they realize that, you know, they're tasting truffle for a week afterwards. These are really potent species, some of them. So go steady. Try it as you go. A bit like think of it maybe as a bit more like spices than, you know, kind of a core component if you're thinking about these more unusual ones and test the flavors first before you put the whole family off. There's a diversity that we just don't appreciate. Because they're relatively new, the diversity of them is relatively new to the Western diet, I think, so we're still like, "Well, what is this weird-looking thing and how do we cook it?"

Jonathan: And if someone's listening to this and saying, "I wanna add some more mushrooms to my diet, I'd like to maximize the potential benefit from doing that, so yes, I'm only gonna eat it if it tastes nice because, like, obviously I'm not going to stick with it otherwise," what would you be saying about the specific types of mushrooms that they should be trying to add?

Robin: The single easiest thing to do is a few fried mushrooms. So it's quite easy to add them as a sort of supplement side to things you're eating. If you don't like mushrooms or someone in your family doesn't like mushrooms, you know, I think, like with many foods, you can get around that by sort of small and invisible incorporation. So I think there's many a child who avows their hatred of mushrooms, but if you chop them really fine and put them in their pasta sauce, you know, they won't particularly notice. These days you can quite often buy even from sort of supermarkets these kind of mixed boxes of different mushrooms. So if you're someone out there who's only ever had the classical kind of white button mushroom and you're like, "Hmm, I wonder," you can pick up a kind of mixed box from mainstream supermarkets and give it a whirl, you know, an oyster mushroom or a, you know, some of these kind of slightly more exotic ones. That might open your eyes a bit more and, you know... And then if you really get into it, you can discover a whole world of interesting, you know, pig's ear truffles growing on elder plants and all sorts out there.

Jonathan: And is one of the takeaways from this that just like when we think about plants, one of the biggest things that we talk about is like trying to get this diversity of plants because they're feeding all of these different microbes. Should I similarly be thinking about this as I really want to get a diversity of mushrooms into my diet rather than there's just like one mushroom which is the best mushroom, and so I should just make sure I'm only eating that one?

Robin: We don't have the data on that, yet, obviously, in the same way that we do for plants. But you know, I'd be pretty confident in suggesting that diverse mushrooms is probably better than a lot of a single one. And actually, you know, that's kind of a good rule for life, like binging on a single thing is generally not advisable. So even if you love mushrooms, you know, I wouldn't eat a kilo a day. So think about that kind of diversity, particularly when we're thinking about the impact on the microbiome. You know, the microbiome loves diversity, so different fungal substrates for your microbiome to grow on is probably gonna be beneficial.

Jonathan: Given all of this, Robin, do you eat mushrooms? And if so, what do you eat?

Robin: I do eat mushrooms. I love mushrooms and actually, I mean, like many people I'm sure listening to this, mostly it's your traditional kind of field mushroom type thing. But you know, if I get the chance, I do like a oyster mushroom in particular, the occasional truffle. You know, if I'm eating a mushroom, my kind of favorite way is fairly sort of straightforward. So you know, heap of mushrooms next to an English breakfast, great. One of my go-to recipes as a student back in the day actually was, you know, those really big fat field mushrooms that are usually quite expensive, but you know, top tip, last thing on a Sunday at a supermarket, they're usually selling them off dirt cheap because they're gonna be horrible tomorrow. And you can stick some breadcrumbs and some lemon on that and a bit of cheese on the top, stick it under the grill. Great and relativ- I mean, the cheese is not so great for you, but everything else in there is pretty good for you.

Jonathan: Amazing. I'm getting hungry just thinking about it. Finally, if you were going to give one tip for someone listening for how to add more mushrooms to their diet, like next week, you've given us many tips, but what would be your one tip?

Robin: Can I do a tip and an anti-tip? Yeah, you can. So my anti-tip is please don't do this by going out and thinking, "That thing looks like a mushroom on my lawn, I'm gonna pick that." That's a very bad idea. Do go to a supermarket or reputable retailer first. That's my anti-tip. My top tip I think I- would probably be to just think about mushrooms a bit more like we think about vegetables rather than this kind of special thing. So if you're thinking, "I'm gonna do chicken fillet tonight, you know, I'm gonna do some carrots. What else do I do with it?" Think about a mushroom rather than a frozen pea, or maybe as well as a frozen pea. Think about mushrooms as a kind of vegetable component that you can put into pasta sauces or things rather than this special thing that you have to somehow put your mushroom cook hat on to deal with.

Jonathan: I love it. Robin, I'm gonna try and do a little summary, and just correct me where I get anything wrong. So I mean, the thing that's sticking with me most of all is that there's a fungus that can only grow on the human head, and ever since you pointed that out I've been thinking about this while looking at your head. And it shows how we coexist with fungi at this incredibly deep level. The other thing I think which is extraordinary is this idea that humans are actually closer to fungi than plants are to fungi, and that does sort of transform the way you think about them as clearly being this source of all of these compounds that you're just not gonna get even if you are eating a lot of diverse plants. And that definitely shifts my thinking about like, oh, I'd really like to have more of these mushrooms in my diet because I'm really trying to get that diverse diet. And the-- one of the reasons why they probably work is you're saying mushrooms are a great food for your microbiome, so actually your microbes are gonna love this. They're gonna feed a whole bunch of good microbes. They can break them down in a way that our body can't and then give us these other benefits. I clearly need to have some oyster mushrooms in my diet because apparently there's 100 times more vitamin D, and since I do live in, you know, northern climes, in the winter I can see the oyster mushrooms that I need to remember to put in the sun are a way forward. There are some amazing nutrients that are inside these mushrooms, and you described this thing that I had never heard of before, the ergothioneine, that is like a whole amino acid that I didn't even knew existed, that I can't make, that I don't get from plants. And you said, like, in the lab it has some really interesting properties. For some reason, like, all our human cells can take it in, but we don't really know what it does. And interestingly, even just like a button mushroom can have this, and this is just an example of the way in... Like, how unique they are. And you talked about them being full of potassium and selenium and vitamin D and vitamin C and beta-glucans, all of these things that you don't have. The other thing that I was really struck by is the idea that we probably all do have fungi in our gut, but it's just at very low levels compared to bacteria, so it's gonna be small. And the latest science is suggesting that we shouldn't think that all fungi is bad for us just because we know that, you know, you can have overgrowths in various ways. So actually, probably it's natural and good to have these, like, low levels inside us, and I think that would be a fascinating thing, you know, to understand more in the data as this continues to grow. And then finally, we talked about how do you get mushrooms, and I think what's striking is any way that you get the mushroom is basically going to be good. So, like, a dried mushroom is still going to be good. It's not like you've lost all the value. If you cook it, it's actually still going to have benefits. The only thing to be cautious of is if you boil it, make sure you drink the liquid, otherwise you are literally putting it into the liquid and throwing it away. And that is very easy to add because it is something that you can eat as a side. So if you're finding it otherwise difficult, you can always just put... You know, fry some mushrooms, put it on the side. And so for me, like, my final takeaway is, like, I need to stop thinking about it as occasionally I have this special mushroom dish, and just think I need to make sure that I have, like, mushrooms in my supermarket shop each week so that I am eating some mushrooms every week alongside the rest, because I'm just gonna up this diversity, and it's this amazing whole new, like, kingdom of things. Like, surely I should be trying to get some of that into my diet.

Robin: That sounds like a perfect summary. I hope you've convinced your son to go into the world of mushrooms.