Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week, we’ll be finding out how body mass is changing in urban and rural populations.

Host: Shamini Bundell

And hearing how rivers across the world are becoming less connected. I’m Shamini Bundell.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

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Interviewer: Benjamin Thompson

Around the world, people’s waistbands are getting bigger. Back in 2016, the WHO estimated that globally, over 1.9 billion adults were overweight and over 650 million of them were obese. But what’s causing this epidemic? Well, new research suggests that a prevalent theory of what’s going on might not be giving the full picture. So, what is this theory? Here’s Majid Ezzati from Imperial College London to explain.

Interviewee: Majid Ezzati

The belief out there is that living in cities actually is the main driver of the obesity epidemic. In some sense, actually, the broad paradigm is that as people move to cities, they consume worse foods, they become less active and hence they become obese.

Interviewer: Benjamin Thompson

If this is correct, there may be significant impacts on future obesity levels, as the United Nations suggest that 68% of the of the world’s population could be city dwellers by 2050.

Interviewee: Majid Ezzati

People believe that we eat more processed and more fast foods if we live in cities. People believe that we use less energy, we are physically less active because living in cities is associated with certain patterns of travel and work.

Interviewer: Benjamin Thompson

So, if that’s the presumed city experience, what’s it like for people living in the country?

Interviewee: Majid Ezzati

In some sense, there has been a romantic view of living in rural areas which is that people eat fresh, healthy foods and are going about their work in active ways, so it has been this extreme, assumed contrast of rural and urban life.

Interviewer: Benjamin Thompson

So, the prevailing view is that urban lifestyles are a big reason for the increase in obesity rates around the world, but is this correct? Perhaps not, according to research that Majid and his colleagues have published in Nature this week. They’ve been looking at the body mass index – or BMI – of rural and urban populations around the world, and how they’ve changed over time. Now, BMI is calculated by dividing an adult's weight in kilograms by the square of their height in metres. The value gives an idea of whether that person’s weight is healthy or whether they might be underweight or overweight. Majid and his colleagues pulled together a lot of data from studies done all over the world between 1985 and 2017.

Interviewee: Majid EzzatiWe had over 2,000 studies. Among them, these studies, they had measures of height and weight of well over 100 million people going back to 1985. So, a lot of measurements.

Interviewer: Benjamin Thompson

By combining data on people’s BMI and whether they lived in a rural or urban setting, the team could build up a picture of how average BMI was changing in individual countries and regions over time. What they found was that although BMIs were increasing everywhere, it wasn’t just down to people living in urban settings.

Interviewee: Majid EzzatiThe majority of the rise in body mass index, in BMI, in the world has actually been due to the rise in rural areas. At the most basic level, the paradigm that we have currently – when we look at all of the data in the world – is actually incorrect.

Interviewer: Benjamin Thompson

In fact, the team suggest that more than 55% of the rise in BMI across the globe was due to increases in rural areas. In some low- and middle-income regions, this figure was as high as 80%.

Interviewee: Majid EzzatiSo, the really interesting thing is actually what’s been happening in middle-income countries. So, these are places like Latin America, parts of the Middle East, north Africa, parts of southeast Asia. In these places, actually, BMI has been going up noticeably faster in rural areas than in urban areas, and a bit more so for women than for men. So, you come to countries like Chile, that in the 1980s there was, if you wish, an urban excess or a rural deficit in BMI, and over time, they have actually reversed. There is now actually higher BMI in rural areas than there is in urban areas.

Interviewer: Benjamin Thompson

This finding – that BMI rates were increasing at the same rate or faster in rural populations – was also seen in those living in low-income countries, with the exception of women in sub-Saharan Africa for whom BMI rose faster in cities than in rural areas. So, what’s going on? Majid thinks that changes to the rural landscape in many regions is playing an important role. He suggests that while improvements to transport infrastructure and an increase in levels of mechanised agriculture are bringing economic and health benefits, they could also mean that people are able to consume more calories and expend less energy, resulting in a BMI increase. Majid also suggests that contrary to the view that urban environments are intrinsically unhealthy, they might actually offer some advantages – giving higher access to healthy foods like fruits and vegetables all year round, for example. Taken together, the results of this new paper rather turn on its head the view that city living is the main reason for the global increase in BMI. Barry Popkin from the University of North Carolina at Chapel Hill, who has written a News and Views article on the new research, thinks the way the team went about analysing the millions of measurements adds weight to their findings.

Interviewee: Barry Popkin

Their methods are solid. They took data that they’ve worked on and developed over a long period of time. They took a lot of national surveys, but when they didn’t have national surveys, they took smaller surveys and extrapolated them and worked on them with very sophisticated statistical methods to kind of replicate national populations. It’s based on a lot of years of work that this team has done they they’ve pulled together into this study.

Interviewer: Benjamin Thompson

Barry thinks that the results of this study will mean that policymakers will have to adjust their efforts when it comes to tackling problems like obesity. He suggests they will need to develop interventions that consider the issues facing people in rural areas.

Interviewee: Barry Popkin

This is going to be country by country. This means countries have to realise that rural areas face the same problems and start to think of either national solutions or think about a special programme for rural areas. Ways to improve activity will help, but it’s really in the food system. They have to find ways to get rural people to start to eat healthier in the same way we need to do it in urban areas.

Interviewer: Benjamin Thompson

That was Barry Popkin. Head over to nature.com where you’ll find his News and Views article, along with Majid Ezzati’s paper.

Host: Shamini BundellLater in the show, we’ll be hearing how up to 1 million plant and animal species could be at risk of extinction – that’s in the News Chat. Up next though, it’s the Research Highlights, read this week by Nick Howe.

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Nick Howe

CRISPR-Cas9 has been a very useful tool for scientists who want to edit DNA. But of course, you can have too much of a good thing. Researchers from Harvard Medical School have been working on a way to block CRISPR when we need to – for example, to stop it from cutting DNA in the wrong places. The researchers developed a method to accurately measure how quickly a specific Cas9 called SpCas9 bound to and cut DNA. They used this measurement to test whether various molecules inhibited SpCas9 activity and would therefore be useful for blocking CRISPR. Restricting CRISPR’s activity to where it’s needed could reduce off-target effects in things like gene therapy. The researchers hope that this could make such technologies safer. For more on that, head over to Cell.

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Nick Howe

Our bodies are full of viruses, many of which are unknown and unexplored by science. Now, researchers have discovered a new strain of virus in a human respiratory tract by sampling DNA from lung donors. The new virus family has been named Redondoviridae, and the study showed that redondoviruses were the second most common virus in the human respiratory tract. The researchers also found that some people with gum disease and some critically ill patients in an intensive care unit had particularly high levels of redondoviruses in their mouths and respiratory tracts, suggesting that this new family could have something to do with disease. You can read more about that study in the journal Cell Host and Microbe.

Host: Shamini Bundell

Next up on today’s show, reporter Adam Levy has been finding out about the health of rivers around the world.

Interviewer: Adam Levy

It’s kind of hard to overstate the importance of rivers. Look at a map of many of the world’s major cities and you’ll see a river running through. And around the world, the flow of rivers brings life to civilisations and ecosystems alike.

Interviewee: Günther Grill

They are amongst the most biodiverse habitats of the world and around 2 billion people worldwide rely directly on rivers for their drinking water.

Interviewer: Adam Levy

That’s Günther Grill, a geographer at McGill University in Canada. But for rivers to be able to support humans and habitats, they themselves need to be healthy. After all, they’re carrying our land’s lifeblood, says John Matthews, Executive Director of The Alliance for Global Water Adaptation.

Interviewee: John Matthews

If you think about constrictions and restrictions in the blood flow within the human body, it often leads to systemic problems. At that large landscape level, we need to keep rivers, as much as possible, connected. There’s the movement of carbon, the movement of species, movement of all kinds of nutrients and resources.

Interviewer: Adam Levy

But we humans are not keeping the world’s rivers connected. Dams, roads, irrigation – there are many ways humans disrupt how rivers flow from source to sea and connect with their flood plains and streams. These prevent rivers from carrying resources freely, and it’s been challenging to get a sense of the scale of this problem. And while the flow of larger rivers has been documented, Gunter wanted to map all the world’s rivers.

Interviewee: Günther Grill

We did not go in the field to look at which river is free-flowing and which one is not – that would be impossible. Instead we relied on satellite imagery and we combined different indicators together, bring that information together, to create an index and with that index we were able to determine if a river is free-flowing or not.

Interviewer: Adam Levy

So, Günther and his collaborators were able to create a map of free-flowing rivers around the world, and we are talking a lot of rivers.

Interviewee: Günther Grill

So, overall, we’re looking at a database of 35 million kilometres of rivers and we can now operate at a scale that is actually meaningful for decision-making in the field.

Interviewer: Adam Levy

John, who didn’t work on this study, is impressed with that they’ve managed to achieve.

Interviewee: John Matthews

So, this is a major assembly of different datasets at very different scales of resolution into something that is coherent and useful. In a sense, this is a kind of health report card for how well we have been managing one of the central attributes of healthy rivers.

Interviewer: Adam Levy

But what does the report card actually show? Well, suffice to say, when it comes to keeping rivers flowing freely, humanity isn’t getting an A+.

Interviewee: Günther Grill

So, rivers in North America, Europe and in parts of Asia, it will be difficult to find longer or major free-flowing rivers, and looking at the results of the study just made me realise how important the conservation of these remaining free-flowing rivers actually are.

Interviewer: Adam Levy

And there aren’t many remaining. Just one third of the world’s longest rivers are free-flowing. Those that aren’t obstructed are in remote regions like the Arctic and the Amazon. The single most common obstruction that prevents rivers flowing freely are dams. But as the world continues to move away from fossil fuels and rely more heavily on renewable resources like hydroelectricity, there’s a tension between combatting climate change and keeping our rivers free-flowing and healthy, as John explains.

Interviewee: John Matthews

A hydropower dam is probably going to last somewhere between 200 and 400 years in its lifetime. That’s a very long commitment, so we need to make sure that if we’re going to go that route, that we understand the full consequences of those decisions.

Interviewer: Adam Levy

Luckily, Günther’s dataset can help inform those decisions. It’s not just a report card of the state of the world’s rivers, but also a tool to keep the world’s cardiovascular system as healthy as possible.

Interviewee: Günther Grill

We’re developing methods to rapidly assess different configurations, different combinations of dams that a developer might want to build, and giving us information about the status of the river, if that particular combination is built.

Interviewee: John Matthews

If we can maintain connectivity within rivers then we have gone an enormous way towards ensuring that these rivers are able to continue to persist and that we are able to maintain a healthy relationship with them.

Host: Shamini Bundell

That was John Matthews, and before him, Günther Grill, talking with Adam Levy. You can read Günther’s paper over at nature.com.

Interviewer: Benjamin Thompson

As always, we finish the show with the News Chat, and joining me this week is Flora Graham, editor of the Nature Briefing. Flora, hi!

Interviewee: Flora Graham

Hi.

Interviewer: Benjamin Thompson

Two stories today, and our first one – well, it’s not a good news story. Research coming out of Paris this week paints a bleak picture for much of the world’s biodiversity.

Interviewee: Flora Graham

This is an absolutely massive study involving 15,000 environmental reports, studies, government reports, and the upshot is that we are absolutely destroying the web of life through mostly agriculture, human activities, those kinds of things.

Interviewer: Benjamin Thompson

Goodness, and what sort of levels are we talking?

Interviewee: Flora Graham

Well, the estimate is looking at the extinction of one million species, some within decades. And of course, it’s not just plants and animals that are affected – it’s humans as well because we rely on these resources for our own survival.

Interviewer: Benjamin Thompson

And who’s come out with these estimates then?

Interviewee: Flora Graham

The name of the panel is the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services – bit of a mouthful – but it’s known as the IPBES. It’s a UN-backed panel, and I think what’s really significant about this group is, you know, this is a worldwide group of people. This is something that’s being signed to by nations from around the world, so it’s really a very comprehensive look at the state of things and the many, many interlocking factors.

Interviewer: Benjamin Thompson

Well, let’s get into it Flora. What are some of the factors that are impacting on species numbers around the world?

Interviewee: Flora Graham

One of the biggest villains here is agriculture activity, so we’re talking about how we grow food, how we harvest meat and then, as well, things like hunting, fishing. So, we are affecting such a huge area of the Earth with this activity that we’re starting to cause major, major effects across ecosystems.

Interviewer: Benjamin Thompson

So, let’s not muck about – up to one million plant and animal species being made extinct is obviously catastrophic. How might that manifest itself in the world?

Interviewee: Flora Graham

So, you have to realise that not only do we rely on plants and animals for things like food – these are the natural resources that drive our economies, they keep our societies moving, they keep the air clean, they keep the climate stable, so all of human existence depend on these ecosystems being in fairly good shape.

Interviewer: Benjamin Thompson

And what are the people at the IPBES saying about this report?

Interviewee: Flora Graham

Well, they’re saying that although we are making positive changes worldwide, we really need to do much, much more. Our goals and aspirations at the moment are not ambitious enough. We need to make transformative changes to our economies, especially how we grow food and meat. We need to change our social and political systems in order to protect much, much more of the habitats that can keep these ecosystems healthy.

Interviewer: Benjamin Thompson

I mean humanity has done a cracking job thus far of making such huge changes – I mean the outlook seems pretty bleak, right?

Interviewee: Flora Graham

Well, I’m not going to sugar coat it – this is not good news. But some of the changes we can make to help improve ecosystems will have positive knock-on effects in terms of climate change, and of course, vice versa – climate change will cause these negative effects on animals to accelerate. With a warmer world, you’ll see more extinctions. With a cleaner world, you’ll see more of these species survive. If we make some of the changes to the way that we fish and grow food, we’ll see that the greenhouse gas emissions of those activities will also fall, so it’s an interlocking system where we can see benefits through our activities all across the board.

Interviewer: Benjamin Thompson

Well, finally on this one then, Flora – what about the sort of practicalities of how we get to where we need to be then in protecting species?

Interviewee: Flora Graham

In general, I think there is widespread agreement that the really practical policy implications of these types of messages is the next natural step, and that’s where we have to get to because of course, we are not talking about 100 years, 200 years – we’re talking about 10 years, 20 years, 30 years, so we need to really get moving. So, it’s time to start thinking about what can leaders do on a national level, an international level, a local level, in order to start really making the big changes necessary.

Interviewer: Benjamin Thompson

Well, let’s move on to our second story today, Flora. This is something that was a Nature exclusive, but it just missed last week’s show. I thought it was super interesting though so I wanted to cover it all the same. What can you tell me about this one?

Interviewee: Flora Graham

Well, we have discovered that the UK is about to open its very first ‘body farm’.

Interviewer: Benjamin Thompson

Right, and question one is then, what is a body farm?

Interviewee: Flora Graham

Well, it’s not somewhere you grow bodies, of course. It is a forensic laboratory where you can leave human bodies in the states of decomposition that perhaps you wouldn’t normally find them, so they are left out for wind and weather, in the soil, out in the air, in water, so that forensic scientists can learn what happens to bodies and, of course, use that knowledge to help people in the future.

Interviewer: Benjamin Thompson

This does seem like something out of a crime novel, but facilities like these do exist in other places around the world, right?

Interviewee: Flora Graham

Absolutely. They’re not commonplace – as you can imagine – but they do exist in the US and the Netherlands are they are an important part of learning how to understand what happens to the human body after it dies.

Interviewer: Benjamin Thompson

Well, one obvious question that springs to mind then, Flora, is how does one go about populating these body farms in the first instance?

Interviewee: Flora Graham

Well, of course, we’re long past the days when medical doctors were digging up corpses. This is all by donation, and apparently – we’re told – that forensic scientists say people are actually very keen to donate. They’re keen to know that, after they die, their body will be contributing to science.

Interviewer: Benjamin Thompson

And why is the UK now looking to open one of these facilities?

Interviewee: Flora Graham

Well, as you probably know from watching CSI, some things are done using animals – pigs in particular are always popular – but some things you just can’t learn from animal studies. You really have to see how the human body decomposes, so this should provide information that’s pretty important to criminal investigations.

Interviewer: Benjamin Thompson

And I imagine this may be quite a divisive area. What are people saying?

Interviewee: Flora Graham

Some people do question the value of body farms, especially those that are perhaps considered maybe a little too public-facing. Of course, it’s a very, very sensitive topic and for example, some forensic anthropologists have said that the sample sizes are just too small, the results are variable and it’s not a good use of human remains. But in the absence of human remains, of course, you do have to rely on animals, so there’s going to naturally be a bit of discussion over how valuable that information is.

Interviewer: Benjamin Thompson

Well, finally on this one, Flora, when is this facility going to open, do we know?

Interviewee: Flora Graham

Well, there’s a lot of things we don’t know about this story. We don’t know when it will open, we don’t know exactly where it will be, although the documents we’ve seen under the Freedom of Information Act do indicate that it will probably be at the Porton Down Lab, which is a well-known location for defence research in the United Kingdom.

Interviewer: Benjamin Thompson

Well, Flora, thank you so much for joining me today. Listeners, head over to nature.com/news for more on these stories. And if you’d like a daily dose of science news delivered straight to your inbox, head over to nature.com/briefing, where you’ll find all the info.

Host: Shamini Bundell

That’s it for this week’s show. We’ll be back next week with more from the world of science. I’m Shamini Bundell.

Host: Benjamin Thompson

And I’m Benjamin Thompson. See you next time.