Is coffee healthy?

Coffee’s earliest consumption dates back millennia, when the tribesmen of Ethiopia used its ground-up berries to help aid concentration during prayer. 

Arriving in Europe in the 17th century, coffee quickly began to replace beer and wine as a favorite breakfast drink. 

In the 20th century, coffee was blamed for high blood pressure and heart attacks, and more recently linked to a rising epidemic of poor sleep

None of this has prevented coffee’s relentless rise. Over 2 billion cups of the stuff are drunk each day. 

So, is coffee a guilty treat as many of us suspect? Or is it a health drink feeding your good gut bacteria? 

In this podcast, Jonathan speaks with James Hoffmann and Tim Spector to find out. They discuss how coffee affects your gut bacteria, your hormones and your heart, whether decaffeinated coffee is healthy, and they discover some of coffee’s most surprising side effects — which could come in handy if you find yourself in the jungle.

James Hoffmann is a  leading coffee expert and author of The World Atlas of Coffee, and co-founder and chairman of the Square Mile Coffee Roasters.

Tim Spector is a co-founder at ZOE and one of the top 100 most cited scientists in the world.

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


[00:00:00] Jonathan Wolf: Welcome to ZOE science and nutrition, where world-leading scientists explain how their research can improve your health.

In Ethiopia, coffee berries have been ground up and boiled for thousands of years. Whether we use it to aid concentration during prayer.They arrived in Europe in the 17th century. And within a few years, there were 3000 coffee houses in England alone. Coffee quickly began to replace beer and wine as a favorite breakfast drink.

Early coffee drinkers felt dramatically improved alertness and coordination by swapping the alcohol for caffeine, handy when earning a living with your hands. However, it was also met with fear with some church clergymen calling it the bitter intervention of Satan.

In the 20th century, coffee was blamed for high blood pressure and heart attacks.

More recently, caffeine and coffee have been linked to a rising epidemic of poor sleep. None of this has prevented coffee's relentless rise. Today, over 2 billion cups of the stuff are drunk each day. So is coffee a guilty treat as many of us suspect? Or is it a health drink? Feeding your good gut bacteria. My expert guests are here to set the record straight with the latest scientific evidence I'm joined by James Hoffmann, leading coffee expert, and author of the world atlas of coffee, and my friend, Tim Spector, one of the top 100 most cited scientists, and my scientific co-founder at ZOE. In this episode, you'll learn how coffee affects your gut bacteria, your hormones, and your heart, whether decaffeinated coffee is healthy, and discover some of the coffee's most surprising side effects, which would come in handy if you find yourself in the jungle. 

James and Tim, thank you for joining me today. 

[00:01:56] James Hoffmann: Thanks for having me.

[00:01:57] Jonathan Wolf: It's a pleasure. Why don't we start with a quickfire round of questions, starting with James. Is there a best way to make coffee? 

[00:02:05] James Hoffmann: No, there's the best way for you, but there's not an, a sort of best overall way.

[00:02:10] Jonathan Wolf: Does coffee affect your sleep? 

[00:02:13] James Hoffmann: Yes, it does. 

[00:02:15] Jonathan Wolf: Can you drink too much coffee? 

[00:02:17] James Hoffmann: I mean, there's a lethal dose of caffeine, so about 150 espressos will kill you. So yes, yes, you can drink too much coffee. 

[00:02:24] Jonathan Wolf: Okay. I'm guessing that most people don't hit that level. I would hope not. And finally, James, is coffee, addictive? 

[00:02:32] James Hoffmann: Complicated, but I'm going to say no. 

[00:02:35] Jonathan Wolf: Tim?

[00:02:36] Tim Spector: I think it depends on how you define addiction. Certainly, if you stop having it, there are side effects. So by some definitions of addiction, it would meet those criteria. But clearly, it's not like heroin. 

[00:02:49] Jonathan Wolf: Brilliant. And Tim is coffee, a high fiber food? 

[00:02:52] Tim Spector: It is, it's probably the drink you have regularly has contains the most fiber. There's more fiber in it than a glass of orange juice.

[00:03:01] Jonathan Wolf: Are there coffee, loving gut bacteria? 

[00:03:03] Tim Spector: There are indeed ZOE's discovered some of them. Yes. And you can tell a coffee lover just from looking at their poop. 

[00:03:11] Jonathan Wolf: Which is a messy way to figure out whether someone likes coffee. 

[00:03:15] Tim Spector: Yeah. You could ask them!

[00:03:15] Jonathan Wolf: And the last question, which we'll go back into more detail, but is coffee healthy? 

[00:03:22] Tim Spector: For most people? It is a healthy drink for those that tolerate it well. 

[00:03:27] Jonathan Wolf: Excellent. And we'll come back and talk. I'm sure a lot more about that. So why don't we start before that James with you just telling us what is coffee? And I guess also, why are we willing to spend, you know, $5 or £3 on a single cup of it?

[00:03:40] James Hoffmann: Okay. So coffee is ultimately the seed of tropical fruit, grows on a shrub between the Tropic of Cancer Tropic of Capricorn around the world. At some point, we worked out that if we take the seed and ultimately roast it, smash it into little pieces and steep it in water, the resulting beverage is quite stimulating.

And that was the sort of early beginnings of coffee. It's obviously evolved a great deal, especially in the last 10 or 20 years. And so part of it is it has caffeine in it and we like that. And I think we quickly grow to enjoy the taste, even though caffeine shouldn't be delicious. It's an insect repellent.

Ultimately that's its purpose in the plant. It's not supposed to encourage consumption quite the opposite, but humans have a funny habit of enjoying the things we're not supposed to. And so recently coffee has become much more specialized, less commoditized, and we've discovered that where you grow coffee, the variety of coffee that you grow, the way that you roast it, the way that you brew it has an impact on flavor.

And we can make it really very delicious and interesting. And I think it's become a sort of small luxury and delight in people's lives day today. This sort of necessary stimulation that they might've wanted in the morning. A little injection of caffeine has become entertaining, and enjoyable. Tasty thing.

And I think we're willing to spend money on that. 

[00:04:50] Jonathan Wolf: Brilliant. And so I guess alongside this pleasure, there's been a lot of discussions back and forth. I think about where the coffee is good for you or bad for you. Why don't we start to dig into that and, both what we think now, but maybe a bit like what I think some of us grew up with stories about how coffee was bad for us. What's the view today? 

[00:05:08] Tim Spector: I was brought up through medical school and as a junior doctor to really warn people off coffee, that it was bad for you. It was a stimulant that overexcited your heart. And that was probably a cause of heart disease and heart failure, heart attacks, and particular abnormal rhythms of the heart.

It was also linked to cancer and other things in the 1980s. And I even wrote a paper on it, myself saying that coffee caused cancer in the pancreas. Which was very good for my career, but it was total rubbish. And in retrospect as much of epidemiology. Yeah. So it's only really, I think the last five years that the evidence has really accumulated so much that it's incontrovertible that the studies are showing that coffee drinkers have less heart disease than non-coffee drinkers and the study, no excess in cancers or mortality to suggest there were any really bad effects. Now I think there's always a caveat to this, and there are some people who are very sensitive to caffeine who might get a pulse that goes faster and they get some real effects off the caffeine, but it certainly doesn't kill them or cause them any permanent damage and they just know to avoid the drink. And that's why these long-term studies have shown that not only is it safe, but it actually has protective properties on the heart. 

[00:06:42] Jonathan Wolf: And do we have any idea? What's going on, like why it might be in fact good for us rather than bad for us?

[00:06:49] Tim Spector: We've got some idea. Obviously, there are many chemicals in coffee that aren't just caffeine. And I think this is one of the sorts of revelations of what we're discovering about foods is that we're fixated on one of the hundreds of chemicals and think that define coffee just by that one, chemical, when in fact there are hundreds of others, and we think that we've discussed fiber and people who do have three or five cups of coffee a day are getting considerable amounts of fiber, which will be of benefit, but it's probably other chemicals within the coffee that have beneficial effects on the heart via our gut microbes. And these are the chemicals called polyphenols. So these are the natural defense chemicals in most plants, but particularly ones that have those bitter tastes and dark colors and are typically expressed in coffee. And so high concentration, these polyphenols are really like rocket fuel for your gut microbes and make them produce these beneficial chemicals that we think have these amazing protective effects on the rest of the body.

Particularly our hearts. We don't yet understand exactly how that happens. So this is still a working hypothesis.

[00:08:07] Jonathan Wolf: And James, any amazing experiences about the health properties of coffee as you've been traveling around the world?

[00:08:13] James Hoffmann: That's a good question. You know, I think it's interesting the way that different cultures have embraced coffee, I think, you know, discovering that they were giving coffee to school kids aged eight in Brazil was sort of shocking to me at one point because we have this sort of like, oh no, it's a grown-up thing. It's an adult thing. It's not like good for you. I, I think other countries are like, no, it's fine. What's wrong with you? Healthwise. It's definitely an interesting one.

I think it's, as someone immersed in the coffee you just see a lot of claims on both sides. And I think it's often, bewildering even for someone inside the industry to understand exactly what's going on and what's good, what's bad, antioxidants, all of those kinds of things that you see around there. And it's a conversation that I'm often hesitant to get drawn into because there is so much misinformation around it.

[00:08:55] Tim Spector: I should just add this as a sort of caveat that the health data show that if you have, it's healthy, between one and five cups of coffee a day. As soon as you get to six or more, you seem to lose that benefit. And we don't really understand why that is, but there might be a nice dose, you know, a sort of safe threshold where the benefits outweigh any risks.

But like anything that has chemicals or mild addictive properties, there might be a sweet spot that works for most people. And of course, we're probably going to talk about this more. There's quite a bit of personalization here. The same cup of coffee is going to have a lot of very different effects on different people.

Averages can be deceptive. You know, that's what epidemiology does. It takes a very broad average, but I think we need to advise people down at the individual level. 

[00:09:47] James Hoffmann: Well, I was just going to say, thinking about that, you know, caffeine is not quite at the level of sweetness, but it's one of the most studied compounds on earth kind of thing.

We've, we've looked at it for a long, long time, and there are recommended guidelines for caffeine consumption of about 300 milligrams a day for an adult. And I wonder if, by the time you hit five cups, you're probably exceeding that level, and essentially while you might be getting some benefits of polyphenols, you'll be getting to see the downside of excess caffeine.

And that's the sort of the tipping point. Maybe. 

[00:10:14] Tim Spector: It sounds very plausible. 

[00:10:16] Jonathan Wolf: So we've got this magic drink. That's pretty cool. Full of fiber and polyphenols and all the rest of it. And it tastes good, James, which I think is very important. How's it made, right? You said it starts with a plant. I think most of us that's not really how we think about it.

And how does this process both affect its taste? And also what impact does that then potentially have on its health? Maybe you can sort of walking us through that from these plants somewhere warm. 

[00:10:41] James Hoffmann: Sure. Well, I'll start at the highest level. We mostly grow two different species of coffee. There's one that's considered superior, which you might've seen sort of, coffee shops using as a term, which is Coffea Arabica so let's say a hundred percent Arabica, which is sort of the better of the two species. The other species we know as Robusta. It grows at lower altitudes. It's much harder as a plant in part because it produces twice as much caffeine because caffeine, as I said is an insect repellent. And so the cheaper coffee actually has a lot more caffeine in it, which I think is something people don't really think about.

And if you think about jumping to the end, cheaper coffees, like Robusta attempt to end up in things like instant coffee. So you're getting a higher dose of caffeine per sort of other potential benefit. Typically speaking, I think some of the other things that are listed like antioxidants, I don't know where you stand on.

Those are seen as lower in Robusta than Arabica. So generally speaking higher quality coffee is considered better or all around in a way it's more complex. It's denser. It's better. So that's the starting point. We then take this fruit. We harvest it, right. We squeezed the seeds out of the fruits like a small grape and inside, there were two seeds like a peanut, so facing each other.

And that's why, if you look at coffee beans, there's a sort of smoother side and around the side. Those ultimately get sort of processed and sorted and shipped to the country that will consume them usually. And that's where we would roast them. So it doesn't get roasted until they are usually in the country of consumption.

Roasting has a massive, massive impact on the chemistry of the coffee bean. The thing that's good about it is that we create flavor. At that point. If you try and drink raw coffee, it's not good. It's disgusting. It's just a hard plant seed. It has none of the flavors of coffee that we sort of experience.

It's got, you know, lots of things in there that seem good, but a lot of those react away during the roasting process. When you roast coffee and it can take anywhere from 90 seconds to 20 minutes to roast coffee when you roast it, this sort of cascade of reactions takes place. 

[00:12:33] Jonathan Wolf: So James, you're basically cooking these seeds? Is that what's going on? 

[00:12:36] James Hoffmann: Yes. Yes. So coffee roasters are sort of a hybrid of a very powerful oven and a tumble dryer. So you're sort of rolling these beans around in the heat. And then what coffee roasters are doing is very carefully controlling how much heat is going in. Because small changes to the rate at which you sort of roast the coffee has a massive impact on taste.

And when you talk to people who do with chocolate or with malt, they're just like, no, no, you just get it to go brown. And it's finished. Coffee is very fussy in terms of the roasting process. So it's hard to do well from a taste perspective. And this is kind of important. The longer you roast coffee, the less acidity it will have because some people struggle with the acidity of coffee.

It's going to be a thing, a topic for a little bit later, and but, the more bitterness you will generate. And so roasting coffee is a kind of balance between keeping enough acidity that it feels interesting as a drink cause a little acidity and food is a wonderful thing, but not overwhelmingly sour, which people don't really like, but also not overwhelmingly bitter.

And some people enjoy darker roasts than others. There's no correct roast level from a taste perspective, but that's the trade-off you'll lose complexity, lose acidity and gain bitterness. The longer you roast coffee. So that's roasting, which is a complicated thing. So a good brew getting a bit nerdy, but if you started with 20 grams of ground coffee, you want about 20% of that to end up in the cup below, that's a good starting point.

That's a good extraction. And we can measure that. We get very nerdy about that. How much water do you use to do makes different drinks. And it's kind of up to you. If you use just a little bit of water, that's a kind of espresso, it's a very strong end product. If you use more water to do the same thing, that's more like a filter coffee and that's as delicious, but just a different kind of beverage. So there's no. Correct strength, but there is kind of good or bad brewing and extraction.

[00:14:22] Jonathan Wolf: And Tim, I hope you are measuring out the exact grams of water that you're adding to your coffee. Cause I think James is going to be disappointed in your otherwise. That's my key takeaway at this point. 

[00:14:32] Tim Spector: There's actually more caffeine, if I understand it, in a week, filter coffee. Then there is espresso. And so most people assume that a strong Italian espresso is going to keep them awake more than a sort of American-style coffee. But when I did the calculations, it appears to be the opposite better off with an espresso. If you want to reduce your caffeine. How does that work?

[00:14:57] James Hoffmann: That's a good question. And what's frustrating is you'll regularly see studies published where there seems to be no correlation between the beverage and the caffeine quantities. You know, they'll sort of secretly shop a bunch of chains in the UK and the caffeine content will be all over the place.

Caffeine is very water-soluble. So essentially the primary correlation is going to be how much coffee was used to make this drink. Now in Italy, a single espresso might come from just seven grams of coffee. So you think, oh, not too much caffeine, but they tend to use a good amount of Robusta in their espresso blends, which have a lot more coffee in there.

So with filter coffee, you might be brewing from say 15 grams of coffee for a 250 ml cup, but that might be, you know, a high ground coffee, a pure Arabica. So not as much caffeine in the raw material, but that's the primary sort of correlation. How much coffee did you use? How much caffeine was in that coffee?

Ultimately, the beverage is going to do a pretty good job of extracting the caffeine, regardless of whether it's a small drink or a big drink. So that's the sort of thing to think about when you're considering how much caffeine you're drinking.

[00:15:59] Tim Spector: So it's pretty hard to tell for the average consumer and, just be aware and assume the worst if you don't want too much. One step of the process, I just wonder if you could touch on this, near to my heart, is fermentation. I know you love the roasting, but, but before that stage, the fermentation, how important is that in the whole flavor combo? Is it as you know, like chocolate, does it have such a big effect or not?

[00:16:27] James Hoffmann: So, yes. Yes. Fermentation has a very big effect on flavor. I think, just to give context to it, a lot of decisions that coffee producers are making are not around taste. It's about getting the best return they can on the crop that they've grown. So most fermentation techniques are about reducing incidences of defects or, or sort of flaws in the coffee. It's a few different approaches.

So as I said, we have this, this cherry, this fruit, and sometimes we're going to squeeze the seeds out and they'll still be covered in a little bit of sticky fruit flesh for want of a better term. And what they would do is let that ferment for maybe 24 hours either, you know, covered, but with access to air or sometimes anaerobically, it can sort of covered in water to break that down so that it's easy then to wash off.

So you sort of have a clean seed to dry before export that doesn't have much sugar lying around that won't go moldy that won't have any kind of floors come into it.

[00:17:20] Jonathan Wolf: And just for a second, just cause we talk about fermentation from time to time, but can we explain a bit for our listeners what's going on when we say it's fermenting for 24 hours, can we explain a little bit more what's going on? 

[00:17:28] James Hoffmann: Primarily what's happening and a lot is going on, with fermentation, so it's never something to say this simply, this, what we're trying to do is break down pectin in this particular case. So pectin is the sort of fruit fiber that's stuck to the seed. So what's happening. There are microbes that are breaking that down, consuming that sort of sugar for want of a better carbohydrate, I suppose, at this point, and essentially causing it to break down.

There is a flavor by-product as a result and there's an impact on all sorts of things from acidity too, to sort of just, sort of the fruitiness of the coffee. In some cases, in other cases, you know, this process does require quite a lot of water, and coffee has historically grown in places that maybe don't have a lot of access to water. There, historically you would have seen that fruit picked and just dried as a piece of fruit, which is hard to do. There will be some. Fermentation there that historically is kind of closer to kind of a controlled rot for want of a better word. It's a kind of chaotic fermentation to just let a piece of fruit dry in the sun.

It's much harder to control, but once you've dried it down, you can sort of hold that sort of dry husk of the fruit off. And you've got access to a dry seed. The fermentation process once coffee roasters get ahold of it, we talk about it just from a flavor perspective. So we'll talk about the sort of more tropical fruit moats of a dry process or a natural process fermentation.

Whereas we might talk about the kind of cleaner, more refined, kind of a juicy berry fruit notes or, or kind of, grape or apple or those kinds of fruit notes that you would get from more of a washed processed coffee and there's a hybrid that you might see called a pumped natural, or a honey coffee, where you sort of have this mixture of things.

And there has an impact on the sweetness on the texture of your cup of coffee, that kind of mouthfeel, how full, how rich it feels. But obviously, there's a lot more going on under the surface. 

[00:19:11] Tim Spector: Generally these are natural microbes just in the environment or do people add specific ones to the mix? 

[00:19:17] James Hoffmann: Historically? It was natural microbes. These days, some of the modern wine-making techniques are coming in and this sort of additions of some bacteria or enzymes to accelerate aspects of fermentation there, which is kind of interesting. And so there's now much more controlled fermentation or intentional fermentation happening, but ultimately to go all the way back historically, it was about how do I get the most valuable crop at the end of this with the least cost to me because you know, coffee is far, far, far too cheap. And so we're sort of forcing people to make these kinds of decisions because they're trying to squeeze as much value as they can. 

[00:19:51] Jonathan Wolf: And one thing that's come up. I'd love to explore a little bit more is fiber.

When I think about fiber, I sort of think about the stuff that you can't easily digest. So I would naturally think, well, that's all the stuff that's left behind in the process that you're talking about. Jane's right. You said I think they're like two-thirds of this. Wasn't going to dissolve into the water.

So I was like, okay, I get that. That's fiber. You chew on it. It tastes terrible. Most of us probably had coffee grounds, in our mouths before. I think what's really surprising is to say, well, in the coffee itself, after I've put it out and assuming that it's, you know, it's not a Turkish coffee with all of its stacks at the bottom like I would have thought, well, there's no fiber in that.

That sounds sort of mad. So Tim, James, can you help us to understand what this is and how fiber is, I guess not as straightforward as maybe we'd assumed? 

[00:20:37] Tim Spector: Yeah. It's a bit of a misconception to think of fiber as this sort of husk that can't be dissolved or digested and just passes through you, you know, and the old concept of roughage was this old fashioned science of how we discussed by, but actually, it's incredibly complex and understudied and there are soluble forms that do dissolve in water and there are forms that dissolve in fats and there are forms that stay insoluble and just sort of end up as a slime inside your gut that does lubricate the gut. So there are all different types of fiber.

And this is, I think, what we're talking about here. And clearly, there are multiple forms of fiber within something like coffee, and that's why some get left behind, but, a large amount does get drunk and get into your intestines. 

[00:21:29] James Hoffmann: Yeah, I think I was sort of genuinely shocked by this research. I think I've lived a life of, you know, I might've experimented with some resistant starches before, you know, that's not much fun to put a drink and kind of consume.

So the idea is that I could get a couple of grams of fiber from coffee. It's actually quite shocking to me, you know, it's a good amount of what is dissolved from the sort of coffee grounds is fiber. And I had no idea. 

[00:21:52] Tim Spector: Yeah. Mean just to put it in context, the average American or Brit, I can't remember which one it is.

Some of between 13 and 15 grams of fiber a day, and decent filter coffee will have something like 1.5 grams of fiber. So. If you managed to get 10 cups of coffee, you'd be getting all your fiber that way. And it just shows you that just having three cups of coffee is about a third of your daily intake. Although we know. We need double that really for good health. 

[00:22:25] Jonathan Wolf: So 15 is not the target. It's like the sort of the low level that most of us are taking. 

[00:22:31] Tim Spector: Yes. But for many people, it's the main source of their fiber at the moment, which is quite worrying. 

[00:22:37] Jonathan Wolf: That's amazing. And Tim, I just want to pick up something else you said where you said there are many sorts of fiber and coffee, so it's not just one type that tends to matter. Right? As we think about food, could you explain a bit more, and does that tie into some of these surprising health properties of coffee? 

[00:22:51] Tim Spector: It may well do. Yes. I mean, the complexity of fiber means that this is made up of different compounds, and different chemicals and all of these are in fact food for our gut microbes.

So each different type of fiber, there is something that reaches the lower part of our intestines. Our colon is where the gut microbes are serves as food for a particular, highly specialized microbe that wants that one. So there might be several types of soluble fiber in coffee, and each one of those attracts a different set of microbes and different species.

And we know that this diversity is really important so, even within one plant like a coffee bean, there are, multiple sources that will feed many different types of microbes. And we know the more diversity of species you have in your gut, the healthier you will be. So it's a great example of how in the past, we haven't really understood this and how the new science is revealing these exciting insights into why something like coffee, which we thought was bad for us is actually good for us.

[00:24:00] Jonathan Wolf: And when we look at how coffee affects us, I mean, we've touched on two things already. You've talked about caffeine and then you've talked about sort of this fiber are those, the two ways that coffee affects us, are there other ways that coffee affects us when we drink it? 

[00:24:13] Tim Spector: Well, it obviously has this effect on our brain. And, we normally have these chemicals in our brain putting us to sleep. And so clearly one of the things of coffee is to neutralize these chemicals, these adenosine molecules. And, it acts as a block of that so that you can alter the normal tiredness cycle. And this is why coffee wakes you up 20 minutes after taking it.

And that's very part of this neurochemical aspect of it, which is mainly related to the caffeine component. And that's something that can have benefits, but also can have side effects as well. 

[00:24:54] Jonathan Wolf: And we had a lot of questions on this, actually around how much is too much coffee. And I think that's related particularly in that context of sleep, but in general, and then a lot of questions about the time of day to drink, coffee, and maybe, you know, maybe start with James because I suspect, again, this is a cultural thing, as well as the scientific thing, isn't it?

[00:25:14] James Hoffmann: So, like I said, with caffeine itself, there's a sort of broad guidelines of about 300 milligrams per day, as your sort of recommended daily limit though, I have to say my own experience, it is so incredibly personal and that people's response to caffeine particularly is, is, you know, a broad spectrum. So just because you're below 300, doesn't mean it's the right quantity for you.

I sort of want to add that in there. And actually one of the interesting things about coffee is just quickly or caffeine that people don't talk about enough. It's one of the few good legal performance-enhancing compounds that are sort of left, though it was temporarily banned by the Olympic committee for a while.

So you couldn't have too much coffee before running a race because it does increase your power output. So, so caffeine before the gym is a good thing. And I think from my own experience, definitely see the benefits of that. 

[00:26:00] Tim Spector: It's only about a 1% advantage. So if you're an elite athlete, 1% is a lot, but for the average weekend, gym goer...

[00:26:09] Jonathan Wolf: I was just thinking that I always really like a cup of tea just before I go to the gym. And this has always made everybody laugh. And now I find it. I mean, let's be honest, this is cause I like a cup of tea a lot, but I'm now going to say it's just about pushing that extra 1% is brilliant. I've got me, I've got, I think every one's got their excuse now for bringing in their super frappucino into the gym.

[00:26:29] James Hoffmann: Though the, I think the tested quantity was about a 200-milligram dose, so it's quite a lot of caffeine, really. So just to sort of caveat my way out of that one just quickly.

[00:26:38] Jonathan Wolf: That's fine. And on sleep. So, I mean, I would say at a personal level, I definitely find that caffeinated drinks affect sleep and we know that sleep is really important for health. That's come up in so many of the different studies that we and others have been involved with. So I've definitely sort of felt that there's a ceiling, which for me is probably about sort of three o'clock that I need to cut back. But interestingly, that wasn't true when I was younger, Tim, like what's going on? Is this true for everybody? They need to stop their caffeine so early in the day, how do we think about figuring out whether you need to stop? And at what time? 

[00:27:12] Tim Spector: The average levels in epidemiology tell us that things change for most people with age. And the ability to break down the caffeine. So there is no longer potent and how quickly it comes out of the system.

So we know the half-life, which is the time it takes to get to half the dose. So you've got, you know, half that coffee is somewhere between five and seven hours, but that means that it could take double that to actually clear the system. And everyone has a different threshold of how that affects them, but also different rates at which they break it down just like alcohol.

And so we found that these averages are fine, but men will actually break down coffee quicker than women. So generally females will have less coffee will have a greater effect on them in terms of their sleep. We also know that cigarette smokers break down caffeine more so to get that hit, they need to actually double the amount of intake than non-smokers. And a number of medications also influenced this as well. So the oral contraceptive pill is, is another one. So, and then on top of that, you've got this enormous, perhaps genetic difference between people that just like alcohol confounds, the whole problem so that I think everyone just has to do their own experiments and don't believe someone else's story about what works for them or not.

They should do their own experiments and try using decaffeinated coffee instead, get someone to switch their coffee is round. So you don't get the placebo effect and test it out for yourself. And, and some people really are absolutely fine drinking a cup of coffee just before going to bed. Others contacted after 10 o'clock in the morning.

[00:29:02] Jonathan Wolf: Yeah, it's amazing. My father-in-law really can have an espresso after dinner and no effect whatsoever. I can tell you for sure that I'm wide. and even if I fall asleep, you know, it's going to really affect over wake up. And I think Tim, you would definitely say that's cancelling all the health impacts of the coffee if it's damaging your sleep.

[00:29:20] Tim Spector: Absolutely. Yes, And anything that damages, your sleep has big knock-on effects. So you need to use this carefully. And I think we need to start thinking about how to give people advice in a personalized manner. You know, that you can test your genes, for coffee now, if you go to something like 23 and me, which gives you a rough idea of, you know, it doesn't explain most of the variation.

It'll just give you a rough idea, of whether you're particularly sensitive. But I think people doing their own experiments is probably the better way forward. And. Yeah, and you can get used to it as well. And I think as James has hinted at, if he did start as a child, probably you build up a pretty good resistance to this so that you need higher doses to actually keep you awake.

That's the other factor. Although, I'm not saying we should be giving all our kids large expressos. 

[00:30:15] Jonathan Wolf: Is that your official advice as a doctor too, Tim? 

[00:30:17] Tim Spector: Might be better than most of the breakfast cereals we're giving them at the moment. So, you know, the Italian breakfast. It might be, the solution we'll have to see.

[00:30:27] Jonathan Wolf: I don't think I'm to be pushing coffee on my children quite yet. So, so one natural consequence, I guess, is to think about decaffeinated coffee. If you like the taste, we actually had lots of questions about this. Maybe like, what is it to start with? And then a lot of questions about, is it safe? Do you get the same health effects, maybe start James, but just help us to understand what it is. 

[00:30:49] James Hoffmann: So decaffeination has done to the coffee as a sort of the raw seed stage. So it's done before roasting and I think the coffee has to be sort of 99.5% caffeine-free at the end of the whole thing. So it's an effective sort of process from that point of view.

It's done a number of different ways. And essentially what they're all trying to do is sort of bind the caffeine into a solvent, into a solution without taking other things out of the coffee as well. You can do it with water and there's a process you'll see called the Swiss water process. That sounds very lovely.

There's one done with what's called supercritical carbon dioxide. Essentially, if you compress CO2 enough, it becomes a liquid and you can use that as a solvent. That's a gross simplification but go with me. And then there are other processes that have lovely names, like the sugar cane process, which sounds great.

 The proper name for it is the ethyl acetate process, which scares people. So you'll tend to see the sugar cane process on the packaging. All of it is completely safe. It's absolutely safe and done well, should have a very limited impact on taste. Decaffeinated coffees are harder to work with as a roaster and they go stale faster.

So if you're a decaf lover, you really want to be buying freshly roasted beans and grinding them yourself for the best experience. And you can have truly, truly delicious decaf coffee. So it can be an uncompromised taste experience, or barely compromised one most of the time, it's not.

[00:32:09] Jonathan Wolf: I was gonna say, I think many people will be surprised by that.

I think it's got a reputation, I guess like many other sorts of processed foods as sort of much worse for you. So I think hearing someone who's such an aficionado be so positive is surprising. Tell us a little bit more about that. I think it may open up a lot of ears. I suspect to maybe rethink this.

[00:32:30] James Hoffmann: No, no, no. I, I think from my point of view, I'm going to be talking about sort of speciality coffee very much still. So this is going to be sort of smaller companies, roasting coffees from distinct places, you'll see farm names or, or sort of more precise regions on the bag. As I said, this process of decaffeination actually changes the density of the coffee bean.

It becomes more porous, so it roasts very differently. And many roasters don't pay enough attention to this because they don't see it as an important product. There's a sort of snobbery against decaf inside the coffee industry too, but there are people who are passionate about decaf because this is coffee for people who just like the taste, not even the caffeine and they're just there for the taste and they get a rough deal.

So, yes, if it's roasted fresh and if it's roasted carefully, it can be good. It will look like a darker roast than it is because it's less dense. The oils will come to the surface of the coffee. Bean it'll look like a dark roast. It's often not actually, but it goes stale really fast because a lot more air can get into the inside of the coffee bean.

It's just much less dense. So if you are buying it as a whole bean using it within two, or three weeks and sort of grinding it fresh each time you'll have a great experience. If you're buying pre-ground decaf from a supermarket, unfortunately, that is, it's a subjective thing. I would say stale. It's food safe. It's totally fine to consume, but it is not what it once was from a flavor perspective.

So freshness is, is the key. It's the secret Baiji care from a passionate roaster who wants to sell you decaf. Some roast is a sort of death before decaf and others are like, no, no, no, this should be great. Let's make it great. 

[00:34:03] Jonathan Wolf: And James, do you let decaf pass your lips on a regular basis? 

[00:34:07] James Hoffmann: Absolutely. I definitely suffer from caffeine.

So my cutoff is about three o'clock in the day. I tend to drink no more than three cups of coffee a day doing tastings. We don't, you know, it's like a wine tasting. You're not drinking it. You're typically spitting it out afterward. So I'm quite cautious around this, but there are times at four in the afternoon when I just want a coffee.

I want that, that sort of moment, that sort of ritual of coffee. And so I drink decaf and I really enjoy it. It can be really. 

[00:34:32] Tim Spector: Instant decaf? You're going to give us a comment on that?

[00:34:34] James Hoffmann: That's oh, I could, but it's complicated. So there exists in the world. High-key billions, decaf, but that's as far as I'll touch on, so it's possible but highly rare.

[00:34:44] Jonathan Wolf: And Tim, any of you from on your side on decaf, is it as healthy as caffeinated coffee? 

[00:34:52] Tim Spector: That's a great question. And there's some indication that it is nearly as healthy. And so most of the studies, lack a lot of the big numbers of decaffeinated coffee drinkers. So the confidence intervals are a bit wider, but, most of the data, not all, of the data points to decaf, having some health properties as well.

So I think this all adds up that if it's well-made coffee that still contains polyphenols, that hasn't been killed off in the industrial process of making perhaps the cheapest, instant coffees, then there will be some benefits also because the polyphenols are still there and the fiber is still there.

And I think that's really a good point. And I was brought up saying that basically, decaf was the devil on it. It also tasted revolting when I was a teenager. So it put me off for a long time. But in my research seeing that in blind tastings to coffee snobs, the decaf version could often win. I think there's a real turnaround. So I think we need to change our minds about high-quality decaf. 

[00:36:01] Jonathan Wolf: And while we're talking about sort of making of the coffee, we got to the roast, in the end, maybe to sort of coming to the final question. We're thinking about it again from a health perspective, we're generally hearing that instant coffee is probably not very good.

Once we're outside of instant coffee, does it matter? 

[00:36:15] Tim Spector: There's a lot of false stuff saying that drip coffee was particularly bad for your heart. And this all came from studies in Scandinavia where this is very common, but I think all of those were found to be spurious. So the current evidence doesn't really distinguish the types of coffee in terms of heart disease.

I don't think we've done direct contrasting trials yet of different types of coffee, but I think if you go for the good quality ones, then you're much more likely to have a healthy outcome. I think you can go with your personal preference, you know, whether you prefer the percolator, the drip or the expresso there's no clear evidence that one is healthier than the other at the moment.

[00:37:00] Jonathan Wolf: And James, I think you said at the beginning that maybe we were free, but I find it hard to believe you haven't got a preference, really. 

[00:37:06] James Hoffmann: Oh no. Like I have a preference, but I'm not going to say that's right. That's a little too much snobbery, but I like paper-filtered coffee. I like the clarity of flavor.

I don't like bits. I don't mind a French press sometimes, but I'd just like clean-tasting cups of coffee. That's just for me. But I like espresso, which is sort of metal filtered too. Within the sort of coffee community, there's still sort of rages of debate around. I think lipids in a coffee cafe all is one of them.

And I for the life of me cannot remember the name of the other one, because they've been occasional papers, sort of correlating these to heart disease. But I know the world of correlating dietary cholesterol to blood cholesterol is a complicated world that I never, ever, ever want to get into. I think coffee drinking broadly seems to be healthy.

And I think the bigger Scandinavian studies have shown. Coffee drinkers have lower all-cause mortality than non-coffee drinkers. That's good news to me. It's not that I want to stop reading there, but I think coffee is ultimately a good and healthy thing, but like all things, the dose is the poison, so to speak.

So like a little moderation, a little awareness, I think for a lot of people, I think that's where things run out of control where they're like, oh, can I have five or six cups of coffee today? I feel a bit weird. Like I think that being mindful of your coffee consumption is a, is a good thing. 

[00:38:16] Tim Spector: And we haven't touched on a few other health side effects of coffee.

Some people might notice the go to the toilet more. Have to pee more when they're having coffee and there is some evidence that it causes increased sensitivity of the bladder. And you might notice this when you have three coffees in succession and you suddenly go into lots of zoom calls and or meetings, and you have to leave the room, which has happened to me, but it's not a diuretic, but it does seem to have when you have large doses, an effect on the bladder wall, that makes you more likely to go to the toilet.

So that's something to look out for. Some people do find it as a useful sort of laxative and help them, which is generally a good thing. If you get the dose, right. So there are a number of these health issues, which are very personalized and will affect some people and not others. And I think it's just important to realize that they can occur and again, a sign that you need maybe titrate the dose, if you are going to the toilet every 15 minutes then something's wrong.

[00:39:17] James Hoffmann: Though I will say the whole stimulating, the bowel thing really threw me for quite a long time because of how rapidly it happens for people. So it's clearly not a kind of traditional sort of digestive reaction, so to speak because people will experience that within a few minutes of drinking coffee.

So clearly there's a sort of hormone, released tied to the experience of drinking coffee, rather than it's getting all the way down and, and sort of stimulating your bowels that way. It's a sort of interesting mechanism from that perspective. 

[00:39:44] Tim Spector: Many people time, on their trips to the toilet buy their coffee. That's right.

So that's why they have to leave the house, you know, a coffee before you leave the house. Not when you're on the bus. 

[00:39:56] Jonathan Wolf: I think that's right. And, and there are people, particularly people who have sort of digestive issues for whom coffee is a challenge if it's tied in with other things. Right?

And so it is definitely one of the things when you're going through exclusion diets and things like this that is often looked at again. I think I guess that ties into this story about, you can say that on average something is healthy, but it doesn't always mean for you as an individual, that it's the best possible thing that you can do.

So the other topic, I think we've talked a lot about coffee and what it does all in its natural state if you can describe all the processing that's just been done as natural. We had lots of questions about what happens when you start to add things to coffee. And basically, the questions are all around dairy, right?

Lots of people are used to drinking milk. And for many of us, when we go to a store to buy this, you get a coffee, which is, you know, a latte or a super-duper frappuccino. Is it still healthy, Tim? 

[00:40:43] Tim Spector: Well, you're still getting the same ingredients, obviously, if you add milk to it, but you're getting the milk.

So generally my view on milk is it's relatively neutral. It's definitely not a healthy drink for some people. You know, possibly slightly negative, but I don't think there's any evidence that disrupts any of the benefits of coffee on its own. It's obviously giving you some extra fats and some other calories and may have an effect indirectly.

I mean, obviously, you know, I actually like the Italian way of having a macchiato. You basically just have about four drops of sort of frothy milk on the top, which, you know, just to take the edge off any bitterness, but the habit of having half milk and half coffee, I think you do realize that having a lot of milk in your diet is probably not a good thing.

And so I think people should perhaps cut back on the milk, but milk per se, I don't think is a major worry for most people, but of course, some people do have lactose intolerance in most parts of the world. So we have to be aware of that, but I think in general, the other it's not bad. The only other caveat here is, that for some people if they're into restricted time eating, most practitioners will have a black tea or a black coffee and not think that they're breaking their fast. And if you add lots of milk to that, then it does definitely stimulate the insulin glucose pathways. And so we'd break the fast. So that might be just another consideration to get people to experiment with trying to get used to having coffee without milk. Cause I think many people in the UK and the US are not used to it. And I think it's something that just, it's a bit of training and culture is going to the southern Mediterranean and you just don't see people putting milk in their coffee unless occasionally at breakfast time.

[00:42:49] Jonathan Wolf: And James any strong opinion from your side about it. Is it sacrilegious to add milk to this drink? 

[00:42:54] James Hoffmann: No. I mean, milk is one of nature's great bitter-blockers and so, you know, I think from that perspective, it does a great job increasing the palatability of what is ultimately often a very bitter, quite harsh product.

The better, the coffee is better, is a very difficult word to use here, but generally lighter roasts, more expensive, higher grown coffees have lower bitterness levels. And so they need less milk to become palatable. So this has sort of benefit there to drink and quote-unquote, better coffee or sort of more premium coffee.

From that perspective. I'm not a milk drinker. It's not for me. And maybe my mind was poisoned early at the beginnings of coffee culture said, and this is from the 1500s, coffee and milk gave you leprosy. That was a widely held belief in, in a great deal of Europe in the sort of middle of the 1600s, really. That was the sort of no-no-go, which I found kind of fascinating.

[00:43:39] Jonathan Wolf: So that seems like a good reason to keep the milk out of one's coffee then. 

[00:43:43] James Hoffmann: We've obviously evolved our understanding since then, but it is just that sort of fascinating tidbit from history. But yes, I totally understand this sort of why people reach for the milk, why they reach for cream, why they reach for sugar.

But I think that this is the upside of quote-unquote better coffee. So to speak, what that's trying to achieve is more flavor, less bitterness. So that's the thinking there. 

[00:44:03] Tim Spector: And the UK and a lot of coffee you get in coffee. The chains are not very good. It's quite bitter. And in a way, drink it with milk. Maybe the only palatable way to have it.

And it's a bit of a vicious circle because the more people buy lattes, the make the roast better to compensate. So it'd be nice to start getting people to experiment without it and see what the coffee really tastes like. That they're trying to get at. 

[00:44:28] James Hoffmann: I would agree a hundred percent so, but I would, you know. 

[00:44:32] Jonathan Wolf: Brilliant.

Well, I think that's been an amazing tour. I think we could keep talking about this for hours, but I'm just going to try and sum up the sort of wide-ranging conversation we've had. So first we started with, you know, coffee is actually the seed of a tropical plant, which is not how we tend to think about it and that amazingly, the caffeine that we are all in such obvious, actually insect repellent. Coffee is healthy. So ignore everything that we might've been told in past years. And the big reason that we think behind that is about all the fiber that you get from. And particularly these polyphenols that Tim was talking to. It's a complex process of making it.

There are two sorts of plants. And I think James, you said the Arabica is the better plant and also lower caffeine, which is interesting as you, I think that it's not always the same caffeine across these. There's a fermentation process involving microbes, and then you roast it, which apparently is a bit like cooking something in a tumble dryer, which is a wonderful image that I'm going to try with my son later.

And that the roasting from James's perspective is sort of the most important step here for really affecting the flavor. Is that right, James?

[00:45:35] James Hoffmann: I think probably so yes. 

[00:45:37] Jonathan Wolf: There really is fiber in this and the fiber is not just roughage. So the reason why you might be struggling with this is that they've got the wrong vision.

A lot of fiber can be soluble in water. So if you're having three or four cups of coffee, you know, you might be getting close to half of the average fiber intake in the US or the UK. So that's quite a lot, but coffee has a lot of impact on us. The stimulation comes from a lot of chemicals, but particularly caffeine.

It really does affect your sleep. James says you can make your coffee the way you like. So there is not one single answer although I think we all heard that he does it with filter paper. So I'm sure we're all going away thinking that's obviously the best way really.

Decaffeinated coffee is not as bad as perhaps we've been led to believe by the sort of thinking about is very cheap coffee. Finally, I think we talked about milk and Tim said, you know, it doesn't do any harm to the health properties of the coffee.

You're just adding milk almost as if you drink it on the side and on the health side, you know, milk is neither a super health drink nor something that's really bad for most people it's sort of neutral. So you can think about that just before we go. I have one final quick question from one of our listeners, George on Instagram, who said, does coffee dehydrate you, which is something that people talk about a lot on social media.

What's the answer? 

[00:46:52] Tim Spector: Quick answer is no, there's no evidence that's a diuretic.

[00:46:57] Jonathan Wolf: So you can keep drinking your coffee and you'll be all right. Wonderful. James and Tim, I really enjoyed that conversation. Thank you so much for taking the time to talk about this wide range from health to taste. And I think everybody will be going away and drinking a cup of coffee right now.

[00:47:11] James Hoffmann: This was great. Thank you for having me. 

[00:47:13] Jonathan Wolf: Yeah. Thank you very much. Bye-bye. 

Thank you to James Hoffmann and Tim specter for joining me on ZOE science and nutrition today. We hope you enjoyed today's episode. If you did, please be sure to leave us a review and subscribe. If you're interested in learning more about ZOE and the best foods for your body, you can head to and get 10% off your personalized nutrition program.

Finally, if this episode left you with questions, please send them in on Instagram or Facebook, and we will try to answer them in a future episode. As always I'm your host Jonathan Wolf. ZOE science and nutrition is produced by Fascinate Productions with support from Sharon Feder and Megan McPherson here at ZOE.

See you next time.