- Today we're talking about one of my favourite subjects, food. Yes, a favourite not just because I very much enjoy eating but also because I'm fascinated by the never-ending buffet of food fads and the ever-evolving evidence about how "unhealthy," in speech marks, things like saturated fat or sugar or meat really are or indeed are not. I'm also interested in food's impact on the planet. In fact, I've hosted documentaries looking at just that and how we might grow or engineer foods to have a smaller footprint in the future. And when it comes to diets-- Atkins, slow-carb, juice, Whole30, 5:2, keto, paleo-- it feels like every month there is a new food plan promising us the world.

There is one, however, that has really gone mainstream, and that is plant-based. A quick look at Google trends shows that plant-based wasn't being searched for much before 2017. It seems to have burst onto the scene in July of that year and then had a steady search incline to a peak in late 2019, early 2020. And I'm sure that you have seen it written on food packaging or restaurant menus, and it's likely that you have also heard claims of the benefits of going plant-based, not just for the health of the planet but also for your health, too.

Now, I don't follow a plant-based diet. I eat meat. I drink dairy. But stats like the ones I've got here written in front of me do make me question that. In a 2016 paper released by the United Nations' FAO, the Food and Agriculture Organisation, they concluded that meat and dairy account for almost 15% of all man-made greenhouse gas emissions, an amount roughly equivalent to the exhaust emissions of every car, train, ship, and aircraft on the planet.

Then there's the Northwestern University study that was released last year that found that eating two servings of red meat, processed meat, or poultry each week was linked to a 3% to 7% higher risk of cardiovascular disease. As I said, stats like these do concern me, because they support the claims that eating certain meats and animal products does indeed contribute to not only a significant impact on the planet but also potentially an impact on my well-being, too.

And that leaves me wondering if I should be switching up what I eat. So let's find out I'm Greg Foot, and today's Which Investigation asks, is a plant-based diet healthier for you and the planet?

Which Investigates is a new podcast from the UK's Consumer Champion. We work to make life simpler, fairer, and safer for everyone, and our mission for this podcast is simple. Find out the facts and see who is actually delivering on the promises we see on packaging, in the press, or shared on social media. Our first season is focusing on claims of sustainability from plant-based to plastic-free, eco travel to electric cars, I'll be figuring out what genuinely reduces our environmental footprint and what is simply greenwashing.

Coming up, I chat with a dairy farmer who says cattle farming can be sustainable.

- It's not the cow but the how. Grass-fed cattle, pastured chickens, free-range pigs, those systems are absolutely potentially part of the solution.

- I hear how plant-based doesn't necessarily mean planet friendly.

- Almond milk takes 15 gallons of water to grow just 16 almonds, and each year more than two billion almonds are produced in California alone. So when you think about that actually, it just seems nonsensical to drink something that uses up so much water to produce.

- And I find out where the story of alternative meats began.

- They had made this promotional video about how the chicken was made. They picked up this discarded feather, took this feather back to the laboratory, and they say from cells from the feather they were able to create meat in a lab.

- We should probably start with what actually is a plant-based diet. However, the problem there is that interpretations differ. I thought that plant-based meant only eating plants or food made from plants, and therefore, anything derived from an animal would be off the menu. That would essentially make a plant based diet the same as a vegan one, loads of fruits, vegetables, nuts, seeds, grains, and no meat, dairy, eggs, or honey.

But the thing is, although that is what plant-based means for some people, for others it doesn't need to necessarily eliminate animal products.

- Plant-based means most of it is plant-based.

- A plant based diet is a diet that is predominantly made up of plant-based foods. You will also eat smaller amounts of meat, fish, dairy, or eggs.

- Vegan means no animal-sourced foods. Very often they are used interchangeably. So when I say plant-based diet, I usually mean a vegan diet.

- As I say, opinions differ. So to try to make this clearer, in this podcast I am going to use plant-based diet as essentially a vegan diet. I think many people and brands, too, in fact, consider them the same. But they opt for the phrase plant-based rather than vegan perhaps for marketing reasons.

I read this on the vegan food and living website that I think sums up many thoughts on that. Consumers see adopting a plant-based diet as a positive food choice but consider vegan a committed lifestyle centred around animal rights and extending out into other lifestyle choices including beauty, fashion, and homewares. So with our terms defined, although I appreciate with some ambiguity left, let's look at what we are eating in the UK right now.

Around 14% of adults, that's over seven million people, are following a meat-free diet. That breaks down into just over three million vegetarians, one and a half million vegans, and it does also include those who eat fish, two and a half million pescatarians, which leaves, what, 44 million adults who do eat meat and lots of it. I was reading a Which article published earlier this year that suggests that in the UK we consume around twice as much meat and dairy compared with global averages. Although, that could be expected, I suppose, when you consider various parts of the world already follow a plant-based diet for cultural and religious reasons.

Here's something fun though that you might relate to. A survey of 2000 adults last year found that on average we are eating just six different meals on rotation every single week, and the most popular food was spaghetti bolognese. Great choice, and of course, with plenty of options for tasty meat-free mince available now, that could be a veggie or a plant-based spag bowl. But would that be healthier?

I will be finding out later, because I want to start this week's investigation with the impact on the planet of rearing all that meat. And I appreciate this is well-trodden ground that you will have likely heard before which is why as you heard in the episode tease, I wanted to speak to a farmer who believes that we can farm cattle sustainably. But first I spoke to a scientist who can take us quickly through the facts.

Shall we get your name and title again just so we can put the doctor in there? It's always good to have ones title that one has worked hard for.

- Sure, Dr. Marco Springmann, senior researcher on environmental sustainability and public health at the University of Oxford.

- Rearing and farming livestock creates a lot of greenhouse gas emissions. You've got the carbon footprint from clearing the land for pasture. You've got the water footprint of the crops you need to grow to feed the animals. You've got to run the farm, transport the meat, and of course, there's the methane that cows and other ruminants release, actually more in burps out the front end rather than the back. Marco was the lead author of a notable 2016 report that said that if we all went vegan, the world's food-related emissions would drop by 70% by the year 2050.

- A good way of getting your heads around it is probably if you took all the savings in greenhouse gas emissions that you could have in a vegan world and put them together and looked at how do those compare to countries and the emissions their countries have? All those emissions savings would be basically the second biggest emitter just after China but before the US and Europe.

- So yes, our current meat-based diets do have a huge impact on the environment. According to an often-cited 2018 study by Joseph Poore and Thomas Nemecek, producing just one kilo of beef creates 59.6 kilogrammes of greenhouse gases. A kilo of lamb creates 24.5 kilogrammes, whereas a kilo of peas and nuts creates less than one kilogramme of greenhouse gases per kilo.

More and more of us are going plant-based, and I should clarify that by us here, I'm referring to developed countries like the UK or the US. And it's easy to assume that because we're going plant-based that must be the trend around the world, too. However, that isn't the case everywhere.

- I think you've seen that in China, for example, their diet didn't traditionally contain dairy products. But now because affluence has increased over the last few years, they are eating more dairy and meat products.

- This is Shefalee Loth, principal food writer and researcher here at Which.

- I think people think of meat and dairy as more premium products and more aspirational foods. So when they get the money, they want to eat those foods, too.

- And that's only going to push up the environmental costs of our diets. And it's not just the greenhouse gas emissions you get from rearing livestock that's impacting the planet. It's also down to the way that we farm them.

- My name is Sir Patrick Holden. I'm the founder and chief executive of the Sustainable Food Trust. I'm also a farmer here in West Wales. We have a 300-acre dairy farm.

Our principle really is to farm as much food as is practically possible without diminishing it. And I think, in a way, in microcosm, that is the challenge for all farmers throughout the world now.

- Half of all habitable land is currently farmed, and as Patrick explained, what's under our feet has an important role to play.

- What we have been doing is diminishing the soil carbon, the soil fertility, and farming a way where biodiversity, nature, cannot coexist with food production. We are causing a lot of pollution. We're using up a lot of non-renewable resources, and the food quality of what we are producing has diminished. And we need to put all those things right.

- I'm fascinated by soil. I did a documentary for the BBC where I actually-- it's all about soil. I loved it, and people don't often think about it. Tell me about why it's important.

- Well, the earth is covered, of course, with a thin layer of organic material upon which all life on land depends. The soil is a fascinating and complex mixture of biological and mineral matter. One way of looking at it is it is the stomach of the plants that occupy the planet. And it's the responsibility of the farmer to enhance the fertility and the health of the soil in such a way that the plants can then drive the maximum nutrition possible from it.

And what we have been doing with industrial agriculture is compromising the health of the soil, mainly with chemical inputs, pesticides, and artificial fertilisers. We need to give them up, not least, for instance, because nitrogen fertiliser is responsible for a great chunk of our greenhouse gas emissions.

- This is one of the big reasons why Patrick suggests that we should continue to farm cattle.

- We're in our 48th year of farming here, our 300-acre farm in West Wales. We've never used a kilogramme of nitrogen fertiliser.

- He says that the best way to renew the soil fertility to up its nitrogen and carbon content is to use natural fertiliser, manure.

- It allows the farming system to absorb the animal manures without causing any pollution or at least minimal pollution. And that's the kind of system that we need to apply throughout the United Kingdom if we want to deal with our groundwater pollution and river water pollution problems.

- I put the suggestion to Marco at the University of Oxford.

- Lots of times people say, oh, cattle produce manure. We need manure as fertiliser, but we don't really need manure as fertiliser. We only need it if we are not prepared to use synthetic fertiliser, but there is really nothing wrong with synthetic fertiliser. The environmental impact associated with fertiliser application, be it from synthetic or manure, is really due to the fact that too much is applied, and you get run off that runs into water systems and pollutes those water systems. So it doesn't really matter if it comes from manure or any synthetic fertiliser.

- Back to my chat with Patrick of the Sustainable Food Trust, as part of the UK dairy industry, are you upset at how dairy farming, cattle farming is portrayed in a lot of documentaries about sustainability or a lot of conversations about this?

- Yes I am. I mean, it's not the cow but the how, and I think we need to differentiate between the intensive animal farming systems which are part of the problem and which are part of the solution. I don't like to think of feedlot beef or permanently-housed dairy cows. I think they're abhorrent.

I know many farmers who are farming grass-fed cattle systems and who are loving their animals, looking after them. Pastured chickens and free range pigs, those systems are absolutely potentially part of the solution.

- But again, putting this point to Marco, is there a sustainable way to farm cattle?

- No, from a greenhouse gas perspective capsule will always emit many more emissions. So it will always be one of the highest emitting foods or food sources that we have. That doesn't mean you can't have any cattle. So clearly there is a bit of room to have a little bit of it, but it doesn't mean that suddenly cattle would be sustainable.

- How do farmers, cattle farmers, feel about your research?

- Yeah, not so good sometimes. I mean, I should really stress that this line of research is not against farmers at all. I mean, we need farmers to grow food, and we all need to be interested that farmers have a stable income and not get out of business. What is really important to think about when thinking about dietary changes and food system transformation is really how do you design a proper incentive system?

- Let me wrap up this impact of meat production on the planet section, then, with one final bit from Marco where he takes me through the amount of feed that different animals take and the relative impacts that they have.

- So far cow, 10 to 50 kilogrammes of feed to put on one kilogramme of body weight, and all that feed usually needs to be fertilised. Even if it's grass, very often it's fertilised, actually. Or pigs, that is usually around six kilogrammes, for chicken, four. Even for fish it's usually two or a bit less than two

- So that results in the fact that animals usually have a multiple the impact that just the plant would have, because the plant, you fertilise it. That's it. It doesn't need any other feed, so to say. And some plants like nitrogen-fixing plants, those would be legumes like beans and lentils, they actually extract on their own nitrogen from the atmosphere. So they actually don't need any fertilisation which makes them very sustainable when it comes to a greenhouse gas emissions point of view.

- Surely everything we've heard so far, then, points towards plant-based as the way to go if we're to reduce our climate impact. Well, if you've heard this podcast before, you'll know it's never quite that simple. We heard Marco say that there is a bit of room to have some cattle, and that is something I'm going to return to later when I ask him what I should be eating and I get a surprising answer.

Those numbers he just shared, though, they suggest that plants can be super sustainable, that growing and eating them would be better for the planet than rearing meat. But this isn't the case for all non-meat foods. Just because something is plant-based doesn't mean it's good for the planet.

We eat quite a few avocados in our house, and yes, that likely started when avo toast was all over Instagram a few years ago, and that drove all those lovely brunch places to start offering it. However, an avocado has a big environmental impact. According to the Water Footprint Network, a single avocado uses 60 gallons of water to grow. That's a huge amount anywhere, especially the water-stressed regions of the world where many commercial avocado crops are grown. And they're not the only go-to plant-based foodstuff with a surprisingly high water footprint.

- Earlier on in the year at Which, we found some research that showed actually although almond milk has quite a relatively low carbon footprint for plant based milks, when you actually look about the water usage, it's incredibly, incredibly high.

- That's Shefali from Which again, and strap yourself in for another shocking statistic.

- 80% of the world's almonds are grown in California which is an area that has suffered tremendous droughts in the last few years. And so for water to be used for almond growth, it needs to be diverted from ground and surface water. It takes 15 gallons of water to grow just 16 almonds, and each year more than two billion almonds are produced in California alone. So when you think about that, actually, it just seems nonsensical to drink something that uses up so much water to produce.

- And that definitely makes me think twice about using almond milk in smoothies or on my cereal. However, flicking back through that Joseph Poore and Thomas Nemecek 2018 study that I mentioned earlier, I saw this. It takes 628 litres of water for every litre of dairy compared to 371 for almond, 270 for rice, 48 for oat, and 28 for soy milk. Which would suggest that, yes, almond milk's water footprint is high, but dairy is even higher.

However, that dairy figure is based on a global average, and that is pushed up by Asia where the water footprint is more than 1,800 litres of water for every litre of milk. If instead we take the European figures, because we don't have UK stats, dairy is closer to 250 litres of water per litre of milk which then puts almond milk, at 371, one top of the list, rice milk, 270, a little way behind that, and then dairy just behind that. Although actually, producer of, I shouldn't be using the term milk there, right?

- Now, this is right. So let me take you back to 2017 and Tofutown. Tofutown are a German plant food company. At the time, they were selling products labelled as tofu butter, veggie cheese, and the intriguingly named rice spray cream.

- Appetising.

- Yeah, quite. Anyway, a German group that monitors unfair competition pointed out that branding nondairy products as alternatives to dairy was, according to EU legislation, against the law, and the European Court of Justice agreed. They said that marketing could be misleading and that milk and related terms can only be used for advertising products that originate from an animal.

Yeah, I think it is drink. In our fridge we've got an oat drink. I like to have it my tea in the morning. There is another, though, plant-based drink that wasn't looked at in Poore and Nemecek's study. That's pea milk, sorry, pea drink.

- Peas, my nemesis vegetable. That was always the veg that was left on the side of the plate when I was a kid.

- Yeah, you and me both. Now hold my hands up here. I really tried to get hold of some for you, but I couldn't get hold of it anywhere. I thought it was more mainstream than it actually is, maybe, but who knows? In the years to come, maybe it's something we'll see everywhere in the shops.

There was a great write up of pea drink on Which? Online, and that says that it's got a really impressive list of environmental credentials, actually. It's quite similar to soy nutritionally, and it's also often used to add protein to loads of different stuff like energy bars, meal replacement shakes, veggie burgers, and even cereal.

- Yeah, I have seen it. I've seen pea protein on vegan protein powder. And protein is something that I want to get into, actually. So that takes us nicely. Thanks, Rob. It takes us nicely from is a plant-based diet healthier for the planet into is a plant-based diet healthier for you?

When a recent survey in America asked over 1,000 Americans aged 18 to 80 what would encourage them to consider plant-based alternatives, over half responded because it is healthier. But is it? Hello.

- My name's Renee McGregor. I'm a dietitian, but I specialise in sports and eating disorders. I have come from a background of both clinical nutrition and have worked with the Paralympic and Olympic teams who went to London, and Rio and I've definitely seen a rise in athletes trying to go plant-based.

So I did a survey with 80 runners. A very high percentage of those runners that had started to go plant-based have struggled to maintain it and sustain it, because actually, in terms of their requirements and their needs, it's not been an easy method of nutrition to provide them with what they need.

- We all need to eat food that provides us with enough proteins, carbohydrates, and fats, the macronutrients, and also the micronutrients, too, vitamins and minerals. But the one that's often mentioned when people raise concerns over whether a plant-based diet can provide enough of it is indeed protein. Protein gives you the building blocks, the amino acids, to grow and repair your body, and you don't just need protein to put on muscle. You need it to build any cell in your body. Let's talk protein. Are all proteins created equally?

- No, so you have two different types of protein. You have high biological value protein and low biological value protein. So high biological value protein are basically animal protein. So chicken, fish, meat, eggs are like your high biological value protein. And what that means is that they contain all the 20 amino acids that we need.

When it comes to low biological value protein, we're talking about beans and pulses, particularly whole grains. So this is where like many, many years ago when we would be giving advice to people who were vegan or plant-based, we would encourage them to mix and match, so things like beans on toast, rice and lentils. This meant that actually the amino acids that were missing in, say, lentils you would get from the rice and the other way around as well.

- However, there is one plant-based protein that appears to reign supreme over the others.

- Tofu and tempeh which come from soy beans, which actually are one of the only sources of plant-based protein that does have all the essential amino acids in them. So they are really good options for people who are plant-based

- It's not just protein we need to consider, though.

- A lot of nutrients, things like iron and calcium, are harder to absorb through a plant-based diet, because plant-based options also tend to have things like phytate and oxalate that prevent you from absorbing the iron and the calcium as efficiently as you would say from dairy or meat. It's not saying you can't, but it's just it's more difficult to do.

If you aren't vitamin C to your serving of iron-rich, plant-based food, that's a really good way of helping to absorb more iron. With calcium, like cooking things can help to improve the absorption of calcium, for example. We also know that if we look at B12 specifically, you cannot get it through a plant-based diet.

- Yes, B12, but what is it, and why is it important? B12 is a vitamin that is naturally present in some foods. Because it contains the mineral cobalt, compounds with B12 activity are collectively called cobalamins. Why is it needed?

Well, basically, it helps the function of the central nervous system, healthy red blood cell formation, and DNA synthesis. A deficiency can cause a wide range of problems including tiredness and fatigue, disturbed vision, and memory loss. Meat is a great source of B12, although interestingly, some farm animals only have sufficient levels of it because they're fed supplements.

If you eat a diet that doesn't contain meat or dairy, you might not be getting enough of this essential vitamin. Although it is present in some vegan foods such as Marmite and miso paste, and many plant-based alternatives and cereals are fortified with it, you can also take a B12 to supplement that provides what you need.

Off the back of my chat with Renee, I had another question. Swapping out high biological protein like meat and dairy for low biological value protein like beans and pulses, wouldn't we need to eat a heck of a lot more and therefore grow more and therefore take up even more land to do so? I put that to Marco. Devil's advocate question, we're going to have to eat a lot more of that crop in order to get all the nutritional content that we require. Is there enough land to do that, to grow enough to feed us all?

- Yep, there is definitely enough land. Because we use so much land to just produce animal feed, if we didn't need to do that anymore, we actually would have a net saving even if we account for the fact that we need to grow more fruits and vegetables. And we could use that land that is at the moment used for growing animal feeds. Globally, that would be a reduction of 10% to 20% in cropland demand.

- So yes, a plant based diet can give you everything you need, albeit with supplements. You'll just have to likely eat a lot more and plan carefully. And that just leaves me with the question I was most interested in for this investigation. Is a plant-based diet healthier for you than a meat based one? Over to Marco again on this, because in his 2016 report, he calculated that if everyone in the world went vegan, it would prevent more than eight million early deaths worldwide each year.

- For the UK, that's having roughly 115,000 less diet-related deaths in a vegan world.

- 115,000 less deaths, that is a big number.

- 20% of all deaths are due to poor diets, and that means eating too few fruits and vegetables, eating too much red and processed meat.

- And because this is quite a claim, I was keen to know more about what the evidence was behind it.

- Where we get that evidence from, so-called observational cohort studies, and they usually follow hundred thousands of people and try to find two groups of people that are the same in terms of all kinds of lifestyle aspects like body weight, smoking status, physical activity, and so on. And then they control for only one thing that differs, for example, eating more red and processed meat. And in terms of, for example, colorectal cancer, then it seems that that is a good indication of a causal relationship.

And there are a couple of other things which one can check that. For example, there are animal studies, there are studies of intermediate risk factors like blood pressure, cholesterol levels, and so on. And all those go together and point towards the causal relationship between, for example, eating more red and processed meat and more disease cases.

- I asked Marco what effect red and processed meat could be having on our bodies.

- It probably has to do with heme iron in animals as far as foods in general that has an impact on disease modulation. Nitrites and nitrates, specifically in processed meat, probably have an impact as well and then lastly sodium, specifically in processed meat. There might be also an impact from the fatty acid composition of meat products because usually they have quite a fair bit of saturated fat and not very many unsaturated fatty acids. So that might add an additional aspect to it.

- The NHS website actually suggests limits for how much red meat we should eat. They recommend 70 grammes or less, and they do say that that can help reduce your risk of bowel cancer. For reference, the smallest packet of mince available in a supermarket is 250 grammes. So that recommendation would mean less than a third of that packet a day or one decent sized sausage.

They categorise red meat, by the way, as beef, lamb and mutton, pork, veal, venison, or goat. So it sounds like if I want to be eating food that minimises my disease risks, then I should be avoiding red and processed meats. But with all these super tasty plant-based burgers and other meat alternatives around, would that be too much of a loss?

Well, I'm going to turn next to whether a plant-based burger is actually significantly healthier for you. But first, the history and the present and the potential lab-based future of these alternative meats is fascinating as producer Rob found out when he chatted to journalist Jenny Kleeman the author of Sex Robots and Vegan Meat which I think you'll agree is a superb title.

- The vegan-- if you can call it the vegan meat industry, I supposed you can, is actually far older than I ever imagined.

- There was a NASA programme to try and grow meat without animals so that astronauts on missions to Mars might be able to eat meat. And I think there were some scientists that managed to successfully grow goldfish meat, but they didn't eat it. The first lab-grown meat to be cooked and eaten was actually done as an art project. But that was always meant to be a kind of comment on our absurd relationship with nature and our appetites.

But unfortunately, it came to inspire the exact opposite of what that artist, Oren Katz, wanted to inspire. In 2011 the first lab-grown hamburger was cooked and eaten, and originally they were going to get some celebrity chefs to cook it, and they were going to get Leonardo DiCaprio and Natalie Portman, famous vegans, to eat it. By then it was slightly scaled down, but I remember watching it on TV at the time in 2011. It was in August, and it was this incredible thing like, oh, my God, we can grow meat without killing animals. Researchers say this technology could be a sustainable way of meeting the growing demand for meat.

- Do you think, and I wonder whether this is one of the things that you took from the work that you did when you were writing the book, that there was a lot of showmanship when it comes to the vegan meat industry? Because it sounds like you met some incredible characters along the way.

- There's this company where I actually went and ate this lab-grown chicken nugget. They had made this promotional video about how their chicken was made. They show somebody taking one white feather from the ground where it's been discarded by this sort of perfect show chicken, like if you imagine a fantasy perfect chicken. They picked up this discarded feather, took this feather back to the laboratory, and they say from cells from the feather, the discarded feather, they were able to create meat in a lab.

- Do you think that it is scalable? Do you think that there will be enough interest to make an impact on the planet for the better?

- I think it will take many years. But at first, this is going to be a very expensive product. It's going to be a kind of curiosity. The first lab-grown meat to ever go on sale went on sale in Singapore in December in a private members' club. And this industry is predicated on the idea that at some point in the near future, there will be meat that is price competitive and taste competitive.

Then we could all get weaned off the idea of eating dead animals slowly, and then it would become a kind of-- quite an outrageous thing to do. Some of it seems like a total fantasy at the moment, and I think anyone who's promising this is going to be on everybody's plates within five years is dreaming a little bit. But I don't think it's totally impossible that this won't be an option in 20 years' time, certainly.

- Cheers, Rob, and thanks, Jenny. I do want to flag too, that not everyone wants a slice of this stuff. My mum is a long-time vegetarian, and she just isn't interested in protein that imitates real meat. But for those of us who are meat eaters, for those people who might consider a plant-based alternative if it looks and tastes like meat, are those options healthier than their meaty originals?

Well, research carried out by Stanford University did find that swapping out red meat for plant-based meat alternatives can indeed lower some cardiovascular risk factors which is great news. However, that study was funded by the Beyond Meat group which makes plant-based meat alternatives. So sadly, we have to take what they say with a pinch of salt, quite a large pinch, in fact.

- These products tend to have a bit of a health halo around them, but actually when we've looked at specific products in the past, we found that's not necessarily the case. In some instances, they can just be as high in fat, in saturated fat and salt, as a meat product that it's meant to be replacing in your diet.

- Renee commented on this, too.

- If you just end up replacing your previous diet with the similar version of a vegan diet or a plant-based diet, then potentially you're still going to have the same impact.

- Yep, those plant based meat alternatives, they might be better for the environment, and they might not contain some of the disease-linked compounds that Marco mentioned earlier, but don't assume that they are quote, "good for you." Sadly, you can't simply swap your barbecue beef burgers for a plant-based alternative and high five yourself over the health benefits. And it's not just these alternative meats that there are health concerns over, either.

- Similarly, something like coconut yoghurt or coconut milk, which has been really promoted and is used in many recipes to substitute cow's milk or cow's yoghurt, is really high in saturated fat. So actually, it's not always a healthier alternative.

- It's all very well becoming plant-based if you feel like it's going to make you healthier, but you still have to make better choices.

- So if I am trying to make sustainable choices to reduce my footprint on the planet, should I go plant-based? Yeah, it sounds like I should. And if I'm keen to eat food that's going to give me the healthiest outcome, that doesn't increase any risk factors of disease, should I go plant-based? Again, yes, it sounds like I should, albeit with me being careful about the choices I make.

But hang on. Marco spends his days researching all this. He is plant-based. He's vegan for exactly these reasons. But when I asked him what he'd suggest I eat, this is what he said.

- It always depends what you want to achieve with your dietary changes. If you want to maximise your health benefits and the environmental benefits, then a vegan diet would be the clear winner. Though if you want a diet that is sustainable enough and healthy enough, you probably can go by with a very low-meat flexitarian diet.

- A very low-meat flexitarian diet which is actually also known as the planetary health diet.

- In one study, we calculated what could we afford collectively in terms of diets if we want to stay within what is sometimes termed planetary boundaries? Those are environmental limits that we have on our planet, for example, not having runaway climate change, not having too much land use and biodiversity loss, not having too much fresh water extraction, and so on.

- The planetary health diet is one that Marco told me everybody could follow without cutting something out completely. And what does it look like?

- So the planetary health diet is really a predominantly plant-based diet. That's how people should really think about it. So the majority of your plate should be whole grains, fruits and vegetables, nuts and seeds, legumes, and a really small portion should only be available for animal-sourced foods.

Red meat, which includes beef, lamb, and pork, you shouldn't have more than once a week, if possible less. White meat like poultry you shouldn't have more than twice a week. Fish you shouldn't have more than twice a week. If you have dairy, you should not have more than one serving per day so either a glass of milk or some other dairy product but not both.

And it doesn't sound awfully strict if you parse it out with this weekly schedule, yet if we compare this to how people eat at the moment, it would still mean roughly 80% reduction in red meat, global red meat consumption, a 90% reduction in the high income countries like the UK. So even though it sounds like everybody could actually do that, if you compare it of how poorly we eat at the moment, it's really quite astounding.

- Personally, the planetary health diet sounds like a very achievable one. I reckon I could even take a bit further. I don't I don't feel like I need red meat every single week or even fish twice a week, to be honest. But I don't feel like I'm ready to go fully plant-based, fully vegan.

In fact, if I return to the definitions of what people take plant-based to be, then for those people who consider it to include some animal products, then perhaps plant-based is closer to the planetary health diet than a vegan one. In which case, yes, absolutely, plant-based would likely be healthier for you and the planet, but a vegan diet could be even more so.

- The rule of thumb is the more plant-based you go, if you do it in a balanced way, then the healthier you would generally be and the more sustainable you would be for climate change.

- Personally, I'm going to give the planetary health diet a go. I think I'm pretty close to it already. I might even go for a slightly more plant-based version of it, but am I slightly disappointed in myself that I've been told that the best thing for my health and the health of the planet is to cut out red and processed meat entirely but yet, here I am embracing this loophole so I can still have some of the foods I enjoy? Yes, maybe, but that doesn't mean that I'm going to get all the macro and the micronutrients I need. Although, that is possible with a carefully planned diet plus a B12 supplement.

It's all food for thought this, isn't it? And I would love to hear where this investigation has left you. Get in touch. I'm @gregfoot on Twitter and Instagram, and Which? is @WhichUK.

Big thanks to those of you who have left a review and rated the podcast over on Apple Podcasts. It genuinely helps others decide whether to click and listen, and it got us to number one in the documentary podcast charts, which we're all very chuffed about. If you haven't yet rated and reviewed it and you are enjoying these investigations, please do go do that wherever you listen.

More episodes are on their way, so follow us to catch them. Our first season is eight episodes long. This is episode four. We are going to do a mid-season special next week where we're going to share some extended sections from the longer conversations I've had with experts during these past four episodes.

It gives us a chance to play out some of the fascinating discussions and more detailed parts that we can squeeze into the edited podcast. We'll then be back with episode five which is going to ask if you may be switching to hydrogen to heat your home in the near future or whether you should be thinking about solar panels or a heat pump. And also as always, I'll be separating genuine eco effect from greenwashing.

If you've got something that you'd like us to investigate in the future, do get in touch. Once again I'm @gregfoot, and Which? Is @WhichUK on Twitter, Instagram, and Facebook. Here at Which? We are making sustainability key to what we do from how we assess the products and services we review to the way we run our whole Organisation. That's why this first season of Which? Investigates is dedicated to helping you make the sustainable choices you've told us are so important.

We've got new reviews and advice every day on which.co.uk that will give you the power to make the best decisions for you and the planet. And if you want to make the most of your money with everyday personal finance tips, then why not have a listen to our sister show, the Which? Money podcast. Today's episode was presented by me, Greg Foot, written and produced by me and Rob Lilly, edited by Eric Bria, and our executive producer is Angus Farka. Special thanks go to Richard Hedlund, Michael Briggs, Emily Seymour, Yvette Fletcher, Olivia Howes and Shefalee Loth. And I'll see you next time.