How your food choices affect the planet

Our planet is overheating. Human society is creating too much carbon dioxide, stopping warmth from the sun from escaping back into space.

As our planet gets hotter, its ice caps melt. This causes sea levels to rise, submerging entire communities. Floods, droughts, and wildfires are already becoming much more common.

Some effects of climate change are now irreversible, but there is still hope. We can all play our part to avoid total disaster. And guess what? Adjusting what we eat might be a much bigger part of this than you’d imagine.

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In this episode, Jonathan speaks with a pioneer in science who will help you understand how your eating habits affect the planet, so you can make informed decisions about the foods you eat and how you prepare them.

Sarah Bridle is a professor of food climate and society at the University of York, in the United Kingdom. She is on the vanguard of a new field, and her research carefully measures the exact impacts of the foods we eat on climate change.

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

This podcast was produced by Fascinate Productions.


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

Our planet is overheating. Human society is creating too much carbon dioxide, stopping warmth from the sun escaping back into space. As our planet gets hotter its ice caps melt causing sea levels to rise and submerging entire communities. Floods, drought, and wildfires are already becoming much more common.

I'm recording this during sweltering heat on the hottest day in the UK's history. Some of the effects of climate change are now irreversible.

But there is still hope. We can all play our part to avoid total disaster. And guess what? Adjusting what we eat might be a much bigger part of this than you'd imagine.

This is a very important subject. So I'm delighted to be joined today by Dr. Sarah Bridle, professor of food, climate, and society at the university of York. Sarah is a pioneer in this new field and her research carefully measures the exact impact of the foods you eat on climate change. This episode will help you understand how your eating habits affect the planet so you can make informed decisions about the foods you eat and how you prepare them. Professor Sarah Bridle, thank you for joining me today.

[00:01:37] Sarah Bridle: That's a pleasure. Thanks for having me. 

[00:01:38] Jonathan Wolf: Let's start as always with our quick-fire questions. So the first is, do I have to go vegan to save the planet? 

[00:01:47] Sarah Bridle: No.

[00:01:48] Jonathan Wolf: Oh, I thought maybe we all had to be vegan. All right, let's go on to the second question. Is a baked potato a great food to reduce my carbon footprint?

[00:01:58] Sarah Bridle: Oh, I'm really torn on that one. I'm gonna go to the one-sentence answer, which is yes, but it depends on how you cook it, and what you eat it with.

[00:02:06] Jonathan Wolf: And that was a trick question because we've been talking about the baked potato earlier as an example of how this can be difficult.

So we'll come back afterward to why a baked potato, which after all is a locally grown food. It's a vegetable. Sounds like it should be perfect. So why sometimes this is more difficult than you think? What would you say to someone who thinks there's little point in changing what they eat to combat climate change?

[00:02:27] Sarah Bridle: Well, I think the main thing people don't really know is actually food contributes about a third of all climate change. And so actually what you eat and the choices you make, turn out to have quite a big impact depending on what we all do collectively together.

[00:02:40] Jonathan Wolf: Brilliant. And I have, a second question, Sarah, what's the one thing I can do today to help save the planet? 

[00:02:48] Sarah Bridle: Well, finding out about the foods that you eat that are the most impactful for climate change. And then thinking about the quantities and maybe the frequency of those foods and for most people on average in the UK and the US, for example, that tends to be animal products.

So, you know, what of those might you maybe eat a bit less of? And then what else could you add in? And maybe some fruit and vegetables and things that are more healthy and good for the planet at the same time.

[00:03:10] Jonathan Wolf: Brilliant. Okay. So why don't we start at the very beginning, Sarah? Why does climate change matter at all? 

[00:03:17] Sarah Bridle: Well, so we are obviously heating the planet.

That's the sort of global heating kind of element of climate change. And that heating of the planet is actually causing extreme weather events as well. So droughts, floods, wildfires coming from that, for example, and, actually for me with an obsession about food, the most worrying aspect of that is the impact of those extreme weather events on the general warming of the planet on food production.

So food is being influenced and affected and harvests are being lost due to droughts, for example, and that is gonna have an impact on how much we can feed the planet and how, therefore, you know, potential issues with trading foods, are people still gonna be happy trading foods between countries after there's been a drought and affecting what we can grow so that there are really worrying implications of us all having a lack of food and potential conflicts, that sort of thing.

[00:04:14] Jonathan Wolf: That definitely sounds bad. I guess a lot of people may be listening saying, Hey, the earth is gonna get a couple of degrees warmer, actually, plants grow better when it gets warmer. Right? For those of us who are gardeners. So you might have thought actually there'll be much more food, but that doesn't seem to be the story that you're telling.

[00:04:30] Sarah Bridle: Yeah so it does depend on where you are on the planet. So there are some places I think it's Iceland, which, you know, we'll be able to grow more food.

But on the other hand, on average globally, if we look up, for example, in the middle of continents, we've got a lot more heating there. 10 degrees of heating there, even if you've only got an average global increase, say two or three degrees, it's a lot bigger in some places than others.

And that on average is gonna have a decrease in food production, just due to the increase in temperature. And then if we also look at the extreme weather events, those are happening in a more coherent way.

So due to the warming of the poles, we actually have more, for example, heat waves happening across say the whole of the Northern hemisphere, which then means that multiple food production places get knocked out at the same time, which then has a much bigger impact on how we respond globally.

[00:05:19] Jonathan Wolf: And I think many of us who are listening to this are definitely conscious that there are more extreme weather events than before. I'm sitting here in London, in my home, up in the attic. When I grew up in London, I could tell you it was never hot in the summer ever. Sarah, so no it's going through this big heat wave at the moment and it's pretty unbearable.

So I guess, you know, I think there are many people who see that in their own lives. So climate change is obviously not good in general. Specifically not good for food production. Why does food matter, however, for reducing climate change?

[00:05:51] Sarah Bridle: Yeah. So actually it turns out that about one-third of all climate change is caused by producing food. And so actually that's bigger if we group it like that, that's bigger than for example, transport or heating.

[00:06:03] Jonathan Wolf: So one-third, that's amazing. That's like huge. 

[00:06:07] Sarah Bridle: Yeah. So that includes clearing land for agriculture. So deforestation. It includes applying fertilizer to the soil to grow crops for animals to eat and for us to eat.

And it includes the animals, the livestock, the methane emissions, for example, cow burps. And it also includes packaging, transportation, cooking, wasted food, and all of those things in between.

[00:06:29] Jonathan Wolf: So a third of everything that we need to sort of constrain if we're to avoid your rather, sort of apocalyptic vision is down to the food we eat. And that sounds like that's actually bigger than the things we're offering worrying about, like, you know, airplanes. Is that right?

[00:06:45] Sarah Bridle: Yeah. So the rest of the climate change is largely caused by fossil fuels, but actually, if we stop burning fossil fuels tomorrow, we'd still be left with most of that contribution from food, because that is actually coming from other causes of climate change.

And if we actually stopped burning fossil fuels and we only had that food contribution, we'd still be on track for causing two degrees of warming by the end of the century from food alone. So we also have to address the food system. 

[00:07:13] Jonathan Wolf: So even if we went to entirely renewable energy sources, actually, if we don't solve food, it's such a big part of this that we're still going to have the sort of heating that you're describing.

[00:07:23] Sarah Bridle: Yeah, well, yeah, two degrees by the end of the century and that's very unevenly distributed and really problematic.

[00:07:29] Jonathan Wolf: So Sarah, as always, these conversations are very cheery, really fast so I'm sure everyone's always really keen to have you around for a dinner party. let's talk a bit about where that is.

And then I'm looking forward to getting onto the positive things that we could do. We always like to talk about sort of actionable changes. So. I'm assuming that not all food is equal, right? So what are the foods that are really bad for the climate? And this is what you have spent the last few years on.

You've written this really impressive book, figuring this out, which is what made me realize just how complicated this is. Help us to understand.

[00:08:02] Sarah Bridle: Yeah. So first of all, a lot of people underestimate how different, different foods are in their contribution to climate change. So people sometimes often will get the right sort of order, but really underestimate how different they are.

So if we have an eight-ounce, steak, and chips for dinner, And we compare that to having a jacket potato and a microwave, potato, and beans for dinner, then those two things were really different and you'd have 20 times as much climate change from the steak and chips dinner as from the potato and beans dinner.

[00:08:33] Jonathan Wolf: So help us to unpack that. So that's like an enormous difference. Like where does that come from? It looked like they were about the same size on your plate. How do you work this out?

[00:08:43] Sarah Bridle: So, what people do is they go through and they look at all the different things. It takes to produce that food and they add all those contributions.

Now, if we look at something like steak, then there are several different contributions. One of the biggest ones is actually that about 5% of all the calories eaten by a cow are burped out as methane, which is a really powerful greenhouse gas. And then we've also got the manure coming from the cow that also contributes methane to the atmosphere and is also nitrous oxide from when that goes into the soil.

So there are a few different ingredients that all adapt to being to that factor of 20.

[00:09:19] Jonathan Wolf: And so you got the cow burping, the methane, I'm guessing that's not the main contribution to the 30% of all of our food. So what else matters as we're thinking about food and presumably it's not like a cow is bad and everything else is good is there's presumably more going on here.

[00:09:34] Sarah Bridle: Exactly. Yeah. So it depends a lot on how you produce the food. So if we think about the cows for example, then those cows, if they're grown on deforested land, if they're grazing land, that's been recently cut at the trees have been cut down to clear land for agriculture, then we would think of that as a lot of greenhouse gas emissions from the carbon dioxide released by those trees when you cut them down.

So we've got deforestation as it makes a big difference to those numbers, but we've also got, for example, if that manure is gonna be spread and be out on the fields and decomposing as nature, had set it up, then that's gonna cause fewer emissions than if that manure is stored for a long time, which happens for example, with intensively rear dairy cows, the manure was stored for a long time.

And that produces a lot of methane when it's stored for a long time. So there are different ways that you can produce that beef and that has an impact on that number.

[00:10:26] Jonathan Wolf: So you've basically done this incredibly complicated calculation of all the little elements, and it's not just the direct amount of carbon dioxide here you're talking about, but actually, you know, if they cut down a tree, then you've lost the tree.

So you're calculating all of these different factors to understand what the total impact is for an individual food.

[00:10:45] Sarah Bridle: Exactly, yeah.

[00:10:46] Jonathan Wolf: And so have you been able to get calculations for all the different common foods that we eat? 

[00:10:53] Sarah Bridle: Yeah. So, I mean, this escalating work done by, you know, hundreds, maybe thousands of people even to do this across all different types of food.

And so if we think about the potato, for example, or crops that are grown for human or animal consumption, the main issue there is gonna be if you put fertilizer on the soil. So putting nitrogen on the soil, for example, then interacts with microbes in the soil. It may be a link to the microbiome, you never know. The microbes in the soil should then turn that into nitrous oxide, which is a powerful greenhouse gas.

And so it only comes down to quite often microbes in the soil and also the microbiome inside the gut of the cow, which is converting some of that food into methane.

[00:11:32] Jonathan Wolf: I think when I'm listening to this and I suspect our listeners as well, it sort of starts to say, well, so I need to be vegan then, to stop climate change, you're telling me this meat is really bad. Is that the conclusion?

[00:11:43] Sarah Bridle: Well, actually, when I first heard about all this, I went vegan for a year because I was so, you know, shocked about the impact of my diet. And I wanted to do something to help, but actually looking back on it, I probably stood there, you know, unpacking my suitcase from a transatlantic trip with the oven on, with my jacket potato in the oven.

I probably popped the shops to get some green beans, which are flown in from somewhere and felt very smug about all the great things I was doing to help with climate change, but actually transatlantic flights, driving to the local shop in the car for one food item, flying food items in for eating, and putting the oven on for two hours all cause more climate change than say, you know, a small piece of meat.

So it's not as clear cut as being vegan, but it's also, I used to love having milk in my tea and I felt very sad because I gave this up for that year, but actually, you know, a tablespoon of milk in a cup of tea, it's a drop in the ocean as it were. It's not a large fraction of the daily climate impact of your food.

So, you know, whatever you're eating, it's contributing to climate change a bit, and having a very small amount of things isn't, you know, gonna make necessarily a massive difference to your overall footprint. So there's no need to be absolutist about it.

[00:12:48] Jonathan Wolf: I think that's a really great message because I think it matches in a lot what we talk about here in general, as you think about food that there's, you know, there's no such thing as bad food. When we're thinking about health, it's about thinking about your entire diet.

And I think there's something quite nice in a space where there tends to be very strong polarization around views that you're saying actually it's maybe not quite as extreme. You don't necessarily have to give something up completely. It's more about understanding quantity.

Could we talk about meat for a minute? Because I think one obvious question as I'm hearing this is, are all meats equal in terms of their climate impact for people who are eating meat?

[00:13:25] Sarah Bridle: No, they're not all equal. And so if we think about the most commonly consumed meats, then beef and lamb would be at the higher end. That's because they're ruminants because they've got this particular stomach arrangement.

If we look at other animals that are commonly consumed, most of them aren't ruminants. So they're things like pigs and chickens, for example, and the climate impact of those will be three or, or fewer times smaller per gram.

[00:13:50] Jonathan Wolf: And is that all because of this methane that you were talking about before?

[00:13:54] Sarah Bridle: Yeah. So the contributions to climate change are different for different animals.

If we look at something like chicken and pigs, actually, then a large fraction of the climate impact is coming from producing the food that they eat.

[00:14:05] Jonathan Wolf: And can you explain that for a minute? So if there's not this methane, specific thing, why is it any worse to eat a chicken than it is to eat a carrot?

[00:14:14] Sarah Bridle: So it's the quantity of food that animals need to eat. So if we're looking at something like pigs, for example, then they need to be fed seven calories for every calorie that we get from the pork that we eat. So there's this kind of inefficiency that comes in when you put human edible food through an animal. So that's the main issue.

[00:14:33] Jonathan Wolf: Got it. So basically it's incredibly inefficient. Like I could have eaten all these carrots myself. I feed them to the chicken. And ultimately I'm having to give the chicken seven times as many carrots in order to give me the same amount of energy as I would've had directly.

[00:14:47] Sarah Bridle: Exactly. And obviously with a cow, for example, I might be eating grass. So it's a bit more complicated there if it's eating grass.

And of course, we might be feeding food that couldn't be eaten by humans to pigs, for example. So there's a lot of interesting research on, you know, how can we try and make that, not just the human edible food, but ultimately the majority of farmland is used for producing food to feed to animals. And so that's 80% of global agricultural land is used to produce food that's fed to animals.

[00:15:14] Jonathan Wolf: And so part of what you're saying is if you reduced the amount that we were eating of animal products, then actually you'd suddenly really reduce the amount of demand just for growing food of any sort. And that reduces the sort of total climate impact.

[00:15:28] Sarah Bridle: Yeah, so land is such a premium right now. We can't really afford to deforest more land. So we've gotta use that land as wisely as we can. And actually, most of the climate solutions use land. So this is why. It's really important to then think, well, actually to produce one calorie of animal product on average is 16 times as much land as producing one calorie of plant-based products.

So we've got this big factor, which is in there. So in this very extreme case, if the whole world went vegan and we look back at that 80% of farmland being used to produce food, to feed animals, if we factor in that factor of 16, it turns out, in the extreme case, everybody went vegan and we'd free up 75% of agricultural land globally for other uses, for example, climate solutions.

So just gives you a sense of the power of that kind of angle.

[00:16:20] Jonathan Wolf: What about byproducts of animals? So what about things like dairy and so milk and cheeses and for the rest of it, how much do we have to worry about those?

[00:16:30] Sarah Bridle: Yeah. So the calculations that have been done, you know, will calculate the climate impact of those things as well. And so we find actually that chicken meat and eggs cause fairly similar amounts of climate change because we still have to feed those chickens. And that's the main thing that's causing the climate change from the meat. So it's also the main thing that's causing the climate change from the eggs, but it's still relatively low.

You know, for all animal products, it's at the low end there. If we talk about something like dairy, then obviously we've got the cows and we've got the burping of the methane again. But if we look at milk, a lot of that's water. So per gram, it looks relatively okay. But actually, if you then turn that into cheese, for example, then cheese per gram comes out similar to something like pork.

So it's still quite a significant contribution. And that's even after you've taken into account, the fact that we also produce meat from some of those animals, so that doesn't really make the problem go away.

[00:17:22] Jonathan Wolf: And from a carbon footprint, would milk alternatives in fact look much better, or because they're so processed, does that actually mean that in the end, theirs is bad? How should people think about this? If they are thinking about, at this point, this lens about trying to reduce our footprint on the planet.

[00:17:39] Sarah Bridle: Yeah. So there've been a number of studies done on plant alternative milk. And obviously, it depends a lot on the details as you say, of how that's processed, for example, but overall, there's not really overlap.

It's about a factor of two or better for the climate to be having those plant milk alternatives compared to dairy milk. Again, you know, other issues about nutrition, not as nutritious, for example.

So many other issues to factor in, in terms of people, often ask me, you know, about different types of plant milk, which is the best one for climate change, but there's not really a clear-cut answer to that because yeah, it depends on how you're producing, for example, oats or soy, or whatever, if it's coming from a deforested region and that would be bad.

But on the other hand, soy is a very efficient way of producing plants and it's a legume so it's fixing nitrogen. So in detail, it's not a clear-cut answer because it often depends on the processing and the packaging and the way that's dealt with as well. But actually, there's still a big difference between dairy and non-dairy.

[00:18:33] Jonathan Wolf: And I think the other thing I guess I'm taking from this is the quantity that you eat is quite important as well.

So, you know, if you're having a small amount of milk because you're just having it with your coffee through the week, then the total impact on your footprint in the week might be quite low if I'm having cereal every day and all the rest of this thing. And so I'm going through many, many pints of it then potentially this is quite significant. Is that also sort of part of the way that you should be thinking about this? 

[00:19:02] Sarah Bridle: Definitely. Definitely. And so for example, as a calculation, I was quite surprised when I looked at, for example, a large latte, if you're having a point of milk in a large latte, which, you know, in a large coffee, which is mostly milk, then that can, you know, blow a large fraction, like two-thirds of your daily budget for your climate impact already just in that one drink. So on the other hand, if you've got a tablespoon and a cup of tea, it's always no difference at all.

[00:19:26] Jonathan Wolf: Okay. So you've already depressed half the listeners at this point.

[00:19:28] Sarah Bridle: I'm sorry.

[00:19:29] Jonathan Wolf: I think they literally have the latte in their hand cause people tend to listen to the podcast while they're walking around, right? They have the latte in their hand, you know, the dog in the other hand, they feel like they're doing everything right. And now they're looking at it and feeling bad. All right. So as little milk is in one latte is already a pretty big climate impact is what you're saying?

[00:19:47] Sarah Bridle: Yeah, sorry.

[00:19:48] Jonathan Wolf: Well, it's at least good to have the information.

So I wanna come back to that question I had right at the beginning about the baked potato. So a baked potato sounds like it should be good, right? Like it's a vegetable. We know if anyone's ever grown potato, like the number of potatoes you grow in a really small area is really high. It can be bought locally, almost anywhere in the world.

So it sounds fantastic. And then I think you described it right at the beginning. Well, actually a baked potato might be much worse than these other things. Can you help us to understand, I guess you explained the first part of this story about what's happening to make the food. So why could a baked potato not just be great from a climate perspective?

[00:20:24] Sarah Bridle: Yeah. So in terms of producing the potato, you're completely right. That it's really quite a low climate impact to produce that potato that you take out of the fridge or, or cupboard, but it really comes down to the cooking.

So if you're, then, then putting the oven on for two hours, to put your one potato in there, then the climate impact of putting the oven on, if it's fossil-fueled oven is gonna be, you know, again, sort of a significant fraction of your daily budget. We used up on just putting that oven on and if you then put the air conditioning on to cool the house down, then that's even worse. On the other hand, if you've turned down your heating because you've got the oven on heating up your house, then it's not such a big difference.

So it's really the energy that it takes to cook that potato.

[00:21:04] Jonathan Wolf: Got it. And so does that mean if you are in a country where renewables have become a really big source of energy and this was an electric oven, then actually you might be just fine? Whereas if I had put it on the gas fire barbecue, for example, you're saying it's completely different.

Is that what you're saying?

[00:21:21] Sarah Bridle: Yeah, you can actually see the fossil fuel there and the gas fire, barbecue burning away. Yeah. I guess we could get into discussions about whether you just cause somebody to burn more fossil fuels to produce more electricity for somebody else, even though you are happily using your renewable electricity.

There's a whole philosophical question there we could get into, but yeah.

[00:21:38] Jonathan Wolf: I think maybe that's a rabbit hole we won't get into. Okay. So what else is really important as I'm trying to figure out how I might change what I'm eating?

[00:21:48] Sarah Bridle: Yeah. Okay. So I would say the oven is problematic in terms of climate change, partly because you are heating up a big metal box for potentially, you know, a significant amount of time.

So I'd say focus on the oven. If it's not in the oven, it's not a big, significant fraction. A microwave, you know, is more efficient. A pressure cooker, or slow cooker, is more efficient. Again, it's not a huge thing compared to all the other components that are there. So I'd say focusing on oven usage would be the main thing to look out there in terms of cooking.

And then in terms of other things where we talked about the type of food, I would say then about air freight. So if you're bringing something by air, then it causes about 100 times as much climate impact as bringing the same type of food by boat. And there's a great book, actually, by Mike Berners-Lee called "How bad are bananas?"

I don't want to spoil the answer for everybody, but, uh, the answer is not very bad!

[00:22:40] Jonathan Wolf: Okay!

[00:22:42] Sarah Bridle: So this is particularly, I guess, thinking about bananas that have come to a long distance by boat, maybe from another continent by boat. A lot of people might think, oh, that's really bad. It's come a long way. The actual climate impact of producing those bananas, which is already relatively small, is still bigger than the climate impact of that transportation.

[00:22:59] Jonathan Wolf: So you're saying, you know, there'll be some listeners right now in Central America who are like, well, I get the banana right next door. That's fine. But you are saying, interestingly, if your banana is being shipped, be it across the ocean to Europe or, I guess also trucked across America to a listener in Chicago, actually, even though it's clearly not local, you're actually saying you don't need to worry too much?

[00:23:22] Sarah Bridle: Exactly. Yeah. It's not really the big thing. So I'd say looking at air-freighted foods and thinking about, you know, do you really need to have those strawberries in the middle of winter? For example, you know, that's the thing to look at next, maybe.

[00:23:33] Jonathan Wolf: So it's not really food miles then, which is something that people, you know, definitely talk about.

It's really air miles. Is it? Is that really the issue?

[00:23:43] Sarah Bridle: Absolutely. Yeah. And in fact, the person who coined the term food miles is really sort of not happy about the way it's taken off in the public consciousness as being the main thing. But yeah, if we could get air miles maybe a bit more on the agenda, that would be good.

[00:23:56] Jonathan Wolf: Well, I think possibly because it overlaps with something that we're also very interested in at ZOE, right? Which is around this idea of food that is less processed, less ultra-processed. And so I think that tends to push this idea of, you know, if you're eating food that is perhaps more locally available, all the rest of these things. And I guess. Those two overlap, but it's really interesting.

So for listeners who are in the UK, you know, one of the things that you often see in a supermarket might be the lamb that has come from the other side of the world from New Zealand or lamb that has come, you know, from the United Kingdom. I would've naturally assumed that the lamb from New Zealand is far, far worse for the environment, because I mean, it's literally come about as far as it can be. Is that wrong, Sarah? 

[00:24:39] Sarah Bridle: Yeah, absolutely wrong.

[00:24:40] Jonathan Wolf: Ugh, I hate it when you say that. Okay. Yeah.

[00:24:44] Sarah Bridle: There's a study about 10 years ago, which looked into this and I mean, it was quite a while ago now, but that study was specifically looking at that question and it found that because of the particular way that they were producing the lamb, at that time in New Zealand, that actually the greenhouse gas emissions of that lamb was slightly lower off the farm than it was in the UK at that time.

And so the climate impact of bringing it by boat was anyway, such a small fraction of that whole thing, that it actually was better at that time with this particular study to get the land from New Zealand and bring it to the UK than it was to get it from the UK.

I think things have changed a bit since then.

[00:25:18] Jonathan Wolf: If I'm sitting in the States right now, then a lot of food, you know, again, I might be, you know, in, in Chicago, this food has come from Florida. And so I'm, I'm not having to necessarily fly something, but this has been trucked a long way in order to deliver me something in, you know, in March that I can eat.

Is that still actually not a big problem because it hasn't gone on a plane?

[00:25:38] Sarah Bridle: Yeah, it's not nearly as big a problem. And actually, if you release greenhouse gas emissions, and burn fossil fuels at altitude, then that actually causes about three times as much global warming as burning exactly the same amount of fossil fuels down on the ground.

So there are these kinds of factors to consider.

[00:25:53] Jonathan Wolf: Got it. So really this is this idea that I'm eating this food and it's been flown from, you know, for example, the Southern hemisphere, if you're in the Northern hemisphere, this is really bad. Is it like I see my asparagus and it's come from Peru or Chile? I have to accept that there might be health benefits from this, but the climate impact is pretty bad.

[00:26:14] Sarah Bridle: Yeah. I mean, if we can quantify that a little bit. So, I mean, it's certainly a very large, it's the majority of the greenhouse gas emissions of that asparagus if it's been flown in, majority of the climate impact of that asparagus is coming from the flight itself rather than the production of the asparagus.

The climate impact of that portion of asparagus is gonna be comparable to a similar amount of low-impact meat at chicken. So it's not as bad as having a similar quantity of beef, for example, in terms of climate impact. But on the other hand, it's up there with low-impact animal products.

[00:26:45] Jonathan Wolf: So we had a whole bunch of listeners asking if are avocados, killing the planet, and it's particularly relevant because this is a food that we think has very strong health benefits for most people.

So in general when we're just thinking about health, it tends to score very highly for, you know, almost everybody who's going through these sort of personalized results. However, if we were thinking about this from the climate, what's the story?

[00:27:09] Sarah Bridle: So avocados are a tree fruit. If we've got a long-lived tree, it's producing these avocados.

It's also sequestering carbon in the soil because it's producing roots under the soil. It's building trunk and branches above the soil. That's taking carbon dioxide from the atmosphere and storing it away in that tree and under the soil. So that is actually a good thing.

The big question comes as to, you know, have you just cut down lots of rainforests to plant avocado trees, in which case that's really bad numerically that comes out as a big problem for climate change.

On the other hand, if that avocado tree's been there a very long time and it's gonna be there for a very long time, then it's actually a net positive in terms of climate impacts, relative to annual crops that are grown in the field, for example.

So it really depends on how it's produced. And if we have a global kind of explosion in, you know, interest in eating avocado, and we need to clear land to produce those avocado trees, then that would be a problem. It really depends.

[00:28:04] Jonathan Wolf: Just before I go on, I just wanna finish on the avocados because I think one of the reasons that people often talk about this is about water consumption.

You talked about the tree growing, but what about the impact of all this water? There's often a lot of talk about the very negative impact on the planet there.

[00:28:19] Sarah Bridle: Yes. Yeah. So if we're having to water that, and if it's, for example, being water, that's being pumped out of underground aquifers, which is depleting that water, or if it's taking out of rivers, which is actually being used for lots of other things further downstream, and we've just taken the water out, that'd be a big problem.

If it's being grown somewhere where there's plenty of water, then it's not an issue. So yeah, it can be an issue, but again, depends on whether it's water that's falling anyway, or whether it's water that has to be going, gone, and got from somewhere.

[00:28:44] Jonathan Wolf: Can we talk about packaging for a minute, because this is one of those things that really stresses me out.

So I'm quite into my recycling. So I like, I wash out the plastic pot for the yogurt and every time I do it, I'm wondering whether I'm actually making everything worse by using this clean water and like washing it out and putting it away than if I didn't do that and it went in to be burnt. And then I see these things that are glass pots, that's starting to increase now and things are getting glass pots or, you know, beans and aluminum.

And I'm really unsure because is that actually better or is it just all a trick, you know, for me on a consumer, because it feels like it's recyclable because you know, we've used glass things. So packaging am I unnecessarily stressed out? How do I think about this? 

[00:29:32] Sarah Bridle: Yeah, I think it is really interesting, isn't it?

Because when you've eaten something, it's a really tangible kind of thing you've still got on your hand after you've eaten it. You're like, oh this is the main issue here when it comes to climate change because I've got this thing left over in my hand and now I've gotta figure out what to do with it. And you've forgotten already about the climate impact.

The thing you've eaten because you've already eaten it. So I think it is very easy to get obsessed with the packaging in terms of something like milk. For example, if we think about a pint of milk in a plastic bottle, Then actually the milk inside the bottle causes 20 times as much climate impact as the plastic that the milk inside.

So in terms of climate change, it's very much what's in that bottle rather than what sort of packaging is it. If it's an animal project like milk. So although I have to admit that it had something absurdly satisfying about having milk in a glass bottle. I mean, I feel very proud as I take my, you know, glass bottles out of the fridge.

So there's maybe some childhood memories there or something, but yeah, it turns out that what's in, it is much more important. On the other hand, if you're having a bottle of water, obviously the climate impact and producing that water is very, very small and the plastic is a large fraction of it. But yeah, for something like milk it's very much about what sort of milk you've got there.

[00:30:44] Jonathan Wolf: What about glass? Is it better? Like if I have the chance, should I be trying to get something that's in glass or aluminum versus something that's in plastic?

[00:30:52] Sarah Bridle: So I did look into this. So there are a lot of issues, obviously with plastic versus glass versus, aluminum, unrelated to climate change.

So for example, you know, plastic, has that really been recycled properly or is it just being thrown into the sea? We, we don't always know that with your council. That's nothing to do with climate change, but it's still to do with the environment. So just focusing on the climate change aspect of it, they're actually not that different.

So if you have glass, for example, then that can be then melted down and then remade back into glass, which is good. The raw materials to make glass are not super difficult to get a hold of, in the first place. So it's not a huge thing. Also, if you have glass it's heavier, so that actually causes more transport emissions because you're transporting a heavier thing.

So it all tends to balance itself out really. 

[00:31:37] Jonathan Wolf: Got it. And what you're saying, I guess, is important is I'm tending to think about climate change and all these other environmental things together. But actually, I think sometimes these might be intentional. Is that right? So you're saying that plastic might be really bad because if it ultimately gets thrown into the environment, you get microplastics and ends up in the sea.

Like that's really bad for the environment and for the fish. And maybe ultimately, even for us as we eat it later, the carbon footprint might even be better than a glass alternative. Is that right? 

[00:32:06] Sarah Bridle: Yeah. They're fairly similar in terms of climate impact. So yeah, obviously, yeah. Let's not throw this stuff in the sea, but yeah, if that's managed properly, then it's very similar in terms of climate impact.

And one of the surprising things that come out of that is something like food in tins. I'd be curious from a sort of health perspective, your thoughts on that.

But, you know, one of the things I started doing was, you know, cooking all these beans and pulses from scratch and, you know, trying to be very careful about how much energy I was using for that, thinking it was making a big difference compared to opening a tin, but actually the climate impact of producing that tin of beans or tin of lentils, for example, is still very small compared to the climate impact of an animal alternative that you might be having. So I think that was a real epiphany moment when I worked that out.

Because I was like, okay, this is great because spoiling all this stuff up from scratch and soaking things overnight, that's a massive hassle, but actually opening a tin is really easy. So sometimes there are steps that people can take that they might have thought were worse, because they're producing all these tin cans left over at the end, but actually it does actually add up to be better for climate change, anyway.

[00:33:09] Jonathan Wolf: So I think the answer in terms of our view actually is surprising when you speak to a lot of nutritional scientists, canned food tends to come out really well because these foods are actually canned almost immediately after they're picked fresh. So very surprisingly, this tends to mean that many of the vitamins and everything that's in them is actually in better shape than if you buy them sort of fresh from the grocers.

So it's nice to hear the alignment we're thinking about this from climate impact. 

[00:33:35] Sarah Bridle: Because we mentioned frozen foods in this as well, you know, you think, oh, we need to eat more fruit and vegetables and more plant-based foods. And then you immediately think of fresh foods. And there are lots of issues with accessing that on a sort of daily basis, but also in terms of food waste, if that isn't all eaten at the supermarket or is less in the bottom of our fridge, whatever.

But yeah, so many ways to consume more plant-based foods that aren't fresh. So the tins that we're talking about now, but also frozen, that was something that I was really curious to look at the numbers for, because yeah, if you freeze those vegetables, for example, those peas, for example, you know, you've put them in the freezer, you've gotta cool them down.

That takes energy. And then maybe, you know, you've gotta heat them up again when you're cooking them. But it turns out that those climate impacts of that freezing and the extra cooking is not a huge deal. So, actually, you have less food waste. Because for example, those things in the supermarket, you're not gonna end up with a whole load of food that's on the shelf, that's past its date because it's in the frozen compartment in the supermarket. So you can end up having less food waste as well.

[00:34:34] Jonathan Wolf: And how big a deal is food waste?

[00:34:37] Sarah Bridle: Massive. Yeah, massive. So I mean globally about one-third of all food is lost or wasted. And so that's bad because we've produced that food and we've caused that climate impact from producing that food and then that was not needed.

And so if we're thinking we just do that calculation of like one-third of all climate change caused by food. One-third of all food is lost or wasted. 10% of all climate change roughly is just food that's wasted. 

[00:35:03] Jonathan Wolf: So does that mean that if we didn't waste our food, we could all still fly somewhere nice on holiday?

[00:35:10] Sarah Bridle: I'll do the calculation, and get back to you.

[00:35:13] Jonathan Wolf: Alright. Alright. Thank you. That's extraordinary. So I did have one question that came through quite a few times, which was whether a sustainable diet is affordable obviously there's a cost of living crisis, and it's for people who've got lots of money.

Can this be affordable? 

[00:35:28] Sarah Bridle: Absolutely. Yeah. There have been some studies on that, which show that actually, if we look at what people are having typically, then that often is cheaper. I think the confusion comes in because in a supermarket, if you go in and you find some of the packets which are labeled vegan, maybe it's the plant burgers or, or some things which have, you know, been specially made to try and look like animal products.

And they've got the big vegan branding on. Sometimes people feel those, those are quite expensive, but actually, if we're looking at things which are, you know, plant-based anyway, for example, tins of beans or, or even bags of beans that you can then cook at home in a slow cooker or a pressure cooker with little energy, then those things themselves are not particularly expensive.

Obviously, it depends on what you're gonna eat.

[00:36:10] Jonathan Wolf: The ratio you were describing right, of going from plants to meat helps to explain why meat, in general, is more expensive than plants. So logically, this seems like it's the right answer. So we've covered a lot of stuff. And I think in a lot of cases, because you're a serious scientist and you've done all the math, the answer is, hey, this is quite complicated.

And you're weighing up this on one side and one on the other, I'd like to come to conclusion with sort of firm guidance for somebody who's listened to this and said like, I'd like to do something with my diet, so that I feel that I can sort of contributing to solving this problem. So if you were going to say, you know, there are three things that you should do in order to reduce your impact on climate change.

What are the three things? 

[00:36:50] Sarah Bridle: Okay. So if we think about quantity, so finding out what foods you eat that cause the most climate change, and then reduce the quantity of those things. And for a lot of people in say the US and UK, then that's on average gonna be animal-based products.

So really what's the quantity? What's the frequency of the things you regularly consume? Maybe focus on those first, rather than things you have on feasts or irregularly. So quantity, and then I would say food waste. So reducing food waste is a bit of a no-brainer really for everybody in terms of reducing cost, as well as climate impact.

And then the third thing I would say is actually, sometimes people come to me and they say, I'm doing this, I'm doing that. I'm doing the other, I've got quite a low climate impact in my diet already. What more can I do?

And actually, if you do the maths again, you know, the answer often is gonna be talking to somebody else about their diet and try to get systemic change rather than individual change. So individuals can have a surprisingly large impact because supermarkets, for example, respond to a small subsection of their population demanding, for example, plant-based foods, that's had a big impact over the last few years.

So individuals can make a difference, but actually, we need some sort of systemic change. And we have a big problem at the moment that if a policy maker, for example, wants to make a new policy, which is gonna help reduce the climate impact of food, that's not popular. And so we actually need to get to a place where if we think about plastics and say five years ago, it's changed a lot in terms of people demanding less plastic in what they're buying.

And that is now getting supermarkets, governments, policy makers falling over themselves to come up with these plastic-free policies and, and ways of doing things. I'd love to see that same kind of change in attitudes to the climate impacts of food and policies around that and see people, you know, trying to tout the benefits of their wonderful new climate-friendly foods.

[00:38:47] Jonathan Wolf: Brilliant. Sarah, thank you so much. I think we covered lots of different areas here. And I think one thing that is really clear is, you know, the complexity of the topic and that, you know, there's not one very simple answer to everything we always try and do a quick summary at the end of what we covered.

So let me have a go and correct me if I've got any of this wrong.

So the first thing is. Amazingly, the food that we eat is a huge part of what contributes to climate change. I think you said a third of the total impact, which I think is a huge surprise for me and many other people. We don't all have to go vegan to stop climate. That's a very extreme call.

However, what we do need to do is probably reduce significantly the number of animal products that we're eating. If you leave the oven on for hours, that's probably also more of an issue than you might have thought. On the other hand, things like frozen and tin goods that you might have thought there was some heavy element from, actually you're very supportive.

And that is because the value of reducing waste is so important. I think you said that food waste was a third of this entire impact. And so for us, actually, maybe one of the biggest things is, well, how much are you thrown away at the end of the week? And how could you change all of this?

And I think the final thing you talked about is, think about reducing air miles. I think you're also saying this really matters. And so just as we think about what we do and what we tell our children elsewhere about the sort of world we want to live in, then actually these are food choices where we can make a difference. And not only by doing this for ourselves but by trying to communicate with other people.

[00:40:21] Sarah Bridle: Brilliant.

[00:40:22] Jonathan Wolf: Sarah, thank you so much. I think it's food for thought. And today we don't have this advice built into the ZOE guide, for example, it's something we talk a lot about as you're aware because we've been talking to you about this, and I think, you know, you see this complexity and you can see how we need to make that available.

So thank you for taking the time. Thank you for spending the hours, months, and years, trying to calculate all of this and sharing it with the rest of us. 

[00:40:44] Sarah Bridle: Thank you so much for having me.

[00:40:45] Jonathan Wolf: It was a real pleasure. Bye bye.

[00:40:48] Sarah Bridle: Bye.

[00:40:49] Jonathan Wolf: Thank you to Professor Sarah Bridle for joining me on ZOE Science & Nutrition today. We hope you enjoyed today's episode.

If you did, please be sure to subscribe and leave us a review as we love reading your feedback. If this episode left you with questions, please send them in on Instagram or Facebook, and we'll try to answer them in the future. At ZOE, we want to improve the health of millions by understanding the right food for each of us to improve our health and manage our weight.

Each member starts with an at-home test, comparing them with participants in the world's largest nutrition science study. If you're interested in learning more about ZOE, you can head to and get 10% off your personalized nutrition program. As always. I'm your host, Jonathan Wolf, ZOE: Science and Nutrition is produced by Fascinate Productions with support from Sharon Feder, Yella Hewings-Martin, and Alex Jones, here at ZOE.

See you next time.