Monthly Archives: September 2016

Who picked British fruit and veg before migrant workers?

Caroline Nye is a PhD student in the Land, Environment, Economics, and Policy (LEEP) institute; her research  focuses on agricultural labour in the UK.

In this blog, Caroline looks at the history of fruit picking and how restrictions of the free movement of Europeans might have an impact on how fruit and vegetables are picked and packed.

This article first appeared in The ConversationConversation logo

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Caroline Nye, University of Exeter

As Britain tiptoes cautiously towards leaving the European Union, there is concern about the impact of Brexit on the farming industry if free movement of Europeans is restricted as part of the negotiations. A whopping 90 per cent of British fruit, salads and vegetables are currently picked and packed by overseas workers.

Yet, Britain’s reliance on migrants to do seasonal agricultural labour is not a recent phenomenon and it’s helpful to look at the history of how British workers turned away from this kind of work to understand the current predicament.

As far back as the 14th century, itinerant Irish migrants were known to travel throughout England and Scotland in search of employment. This became more prevalent by the end of the 18th century when groups such as the “spalpeens” and “tattie howkers”, large travelling gangs of Irish men, women and children, would help bring in the annual harvest. Such migration, not only from Ireland, but also from the Welsh hill counties and Scotland, coupled with itinerant English labourers, was essential to meet the labour demands that the resident workforce alone could not.

There were a number of reasons for this shortage of labour. From the end of the 18th century until the mid-19th century, labour requirements in agriculture were increasing, due to more labour-intensive crops, such as turnips and potatoes, and the adoption of a new crop rotation system. At the same time, the number of full-time farm workers was shrinking, as they were either pulled towards jobs created by industrialisation, or pushed out by mechanisation. On top of this, groups who could have previously been relied upon to help out at harvest time, such as those working in rural textile industries, began to move away from rural areas towards factory work in towns.

Child labour and gangs

Prior to the introduction of the Gangs Act in 1867, a large proportion of those performing seasonal work were women and children who provided cheap labour to both gang masters – a term still used today for individuals who organise and employ groups of workers for casual work on agricultural land – and farmers. This new law forbade children under the age of eight from working the land, after the 1860s witnessed a rise in public concern over the exploitative nature of “ganging”. A series of new education laws soon followed, making school attendance compulsory for children between the ages of five and 12, drying up a significant source of seasonal labour. As more women began to move into the service sector towards the end of the 19th century, there was also a decline in the supply of female agricultural labourers

The British Women’s Land Army cropping beetroots in World War II. British Ministry of Information/Wikimedia

But numbers of workers needed for harvesting remained high, especially following the Irish famine in the mid-19th century, which saw migrant numbers contract significantly. Some of that work, especially hop-picking, was carried out by townspeople, working class families often coming from London or the Black Country for their summer holidays. Many of these people continued to work alongside soldiers, prisoners of war or the Women’s Land Army during both world wars. In the early 20th century, agricultural gangs also employed British people, shipping them from Yorkshire to the East Midlands, for example. But gradually these workers became less willing to travel so far.

Post-war reliance on migrant workers grows

In response to labour shortages following World War II, the Seasonal Agricultural Workers Scheme (SAWS) was introduced in 1945, allowing foreign nationals to temporarily reside in the UK in order to harvest fruit and vegetables. The bulk of SAWS workers were Eastern European or from the former Soviet Union. Although initial quotas were low, farms quickly began to rely on these workers, causing quotas to steadily increase to 21,250 in 2009. In 2013, the scheme was scrapped due to the increasing availability of workers from within the EU.

Number of SAWS work cards issued by nationality, 2004 to 2012. For 2012, data are only up to September 30. Migration Adivsory Committee analysis of UK Border Agency Management Information

Despite this, it was only after the 1990s that British agriculture became heavily dependent upon international migrant workers. This was sparked by power becoming more concentrated among a small number of large corporate retailers. This meant that the bargaining power of farmers became greatly reduced, resulting in fast declining margins.

This power shift largely transformed agriculture as an industry, rapidly moving away from farming as a “culture” to a more intensive industry. Where technology has not stepped in, many farms have had to extract greater efficiency from their workers, at a lower cost, just to survive. This has resulted in a move away from the more paternalistic role of farmers to their workers, to one that is more distant and bureaucratic, further dissuading locals from wanting to do the work.

Back to the land?

Positions left empty if EU migration is restricted following Brexit could theoretically present a solution to high unemployment rates in the UK. But the fact is that many British people simply do not want to carry out seasonal labour because incentives for doing so are very low. Changes in the composition of rural populations mean that areas of high unemployment are often located at significant distances from the farms offering work. Seasonal jobs are also known to be low-paid, hard work, with long hours, and are often associated with unfavourable conditions and diminished social status. Domestic residents prefer permanent employment or complete withdrawal from the labour market onto the social security system.

Migrant workers are less likely to perceive the work as “dead end” and rather see it as a temporary step allowing them to earn an income that has more worth in their home country.

Schemes to encourage British workers back to the land have largely failed. Where they have tried, some farmers state that after several days of work, many do not return. But question marks hang over rhetoric arguing that Brits are too lazy, unavailable, or incapable of doing the work, or that they have an inferior work ethic to overseas workers.

The use of technology so far has proved challenging in the harvest of fragile soft fruits and vegetables, but it is likely that the future will see a gradual move towards the use of robots. Until then, unless food prices change or new systems emerge encouraging domestic workers to pick our fruit, British farms are likely to remain highly dependent on overseas workers.

The Conversation

Caroline Nye, PhD candidate, University of Exeter

This article was originally published on The Conversation. Read the original article.

How Ross Poldark was a victim of Cornwall’s changing industrial landscape

Dr Joseph Crawford, English lecturer in College of Humanities, takes a look at hit BBC series Poldark. He asks if the main character, Ross Poldark, was victim of the changing face of industry in the South West.

This post first appeared in The ConversationConversation logo

Joseph Crawford, University of Exeter

In July 2016, the BBC announced the commissioning of a third season of costume drama Poldark, months before the second series was even due to be broadcast. This represents an impressive vote of confidence in the series, especially as season two will apparently not be repeating the famous “topless scything” scene which won the National Television Awards’ prize for TV Moment of the Year.

The real pivotal moment depicted by Poldark, however, is one of historical change in south-west England. In the mid-18th century, Cornwall and Devon were major commercial and industrial centres. Cornwall’s tin and copper mines were some of the largest and most sophisticated in Europe, while the profits from the Cornwall and Devonshire wool trade helped make Exeter one of the biggest and richest cities in England.

By the mid-19th century however, much had changed. The rise of the mechanised cloth industry in England’s North and Midlands sent the south-western wool trade into serious decline. And while Cornwall’s mining industry survived well into the 20th century, it experienced repeated crises from the 1770s onwards. This was primarily due to newly discovered tin and copper mines elsewhere in the world, leading to the large-scale emigration of Cornish miners to countries such as Mexico, Australia and Brazil.

The era depicted in Poldark shows the region on the very tipping-point of this transition. Ross Poldark’s struggles to keep his mine open and profitable are symptomatic of the economic difficulties experienced by the region as a whole during the late 18th and early 19th centuries.

As south-western towns lost their traditional role as centres of trade and industry, their focus shifted increasingly to tourism. This was especially true during the long years of the Napoleonic Wars which form the backdrop to the later Poldark novels. Cut off by war from their favoured resorts in France and Italy, a generation of English tourists began taking holidays in Devon and Cornwall instead.

By the late 18th century, writers in Devon were praising their native county for its natural beauty and its ancient history, rather than for the wealth and industry of which their parents and grandparents had been so proud. By the mid-19th century, the same was increasingly true of Cornwall.

This economic shift led, in turn, to the development of the Victorian mythology of the “romantic South-West”, still beloved of local tourist boards today.

This mythology is built upon a version of the region’s history which emphasises its remote and wild character, playing on associations with Merlin and King Arthur, druids and witches, smugglers and wreckers and pirates.

Like most costume dramas, Poldark’s primary concern is with the travails of cross-class romance. But it is also a narrative about de-industrialisation, and about the struggle of local businesses to remain competitive and economically viable within an increasingly globalised economy – a story which has some resonance in early 21st-century Britain.

The poverty of the Cornish miners with whom Ross Poldark identifies is not simply the result of gratuitous oppression. Instead they are the victims of a new economic order which has little interest in preserving local industry for its own sake.

Wild West

The show has certainly not been shy about making lavish use of the beauty of its Cornish setting, and has already triggered something of a tourism boom, with visitors flocking to the region to see for themselves the moors, cliffs, and beaches which Poldark employs to such dramatic visual effect.

Industry by the sea.
Shutterstock

But it also depicts the historical struggles of the region’s inhabitants to preserve the South West as something more than just a pretty place for other people to visit on holiday. In this sense, it is rather symbolic that season one of Poldark ends with Ross being falsely accused of wrecking. The legend of the Cornish wreckers, which reached its definitive form in Du Maurier’s Jamaica Inn, is founded on extremely slender historical evidence, but it persists because it fits in so neatly with the Victorian mythology of the South West in general, and Cornwall in particular: a mythology which viewed it as a lawless and desperate land, filled with crime and adventure, and remote from all true civilisation.

In Poldark, the looting of the wrecked vessel is motivated by hunger and poverty, which have in turn been caused by the economic depression besetting the region. But after spending the whole season struggling against Cornwall’s industrial decline, Ross finds himself in danger of being absorbed into a new kind of narrative about the South West – one which will have no place for men like him, except as picturesque savages.

Of course, in this respect, Poldark rather wants to both have its grain and (shirtlessly) reap it, too. Ross Poldark and Demelza appeal to their audience precisely because they embody the kind of romantic wildness which, since the Victorian era, has been the stock-in-trade of the south-western tourist industry.

They are passionate, free-spirited, and dismissive of class boundaries and social conventions: hardly the kind of people that the self-consciously respectable merchants and industrialists of the 18th-century South West would have wanted as their representatives or champions. But by setting its story of class antagonism against the backdrop of this crucial turning-point in the history of the South West, Poldark does serve as a reminder that the quietness of the region, which has proven so attractive to generations of tourists, is not the natural state of a land untouched by commerce or industry. It is the silence which follows their enforced departure.

The Conversation

Joseph Crawford, Lecturer in English, University of Exeter

This article was originally published on The Conversation. Read the original article.

Melania Trump, the Daily Mail and a history of libel tourism

Dr Timon Hughes-Davies, a lecturer in the Law School looks at the recent complaint between Melania Trump and The Daily Mail. 

This article first appeared in The ConversationConversation logo

Timon Hughes-Davies, University of Exeter

Readers of the Daily Mail were recently treated to a fairly rare event: the paper published a retraction of a news story it had run about Melania Trump, the wife of the Republican presidential candidate and prospective first lady of the United States. The retraction related to a story published both in the newspaper and the Mail’s website, which repeated allegations from an unofficial biography of the third Mrs Trump.

These allegations – which are recited in the complaint and have been widely repeated on the internet – relate to her immigration status, the circumstances in which she met her husband and her employment when she first came to the United States. Given her husband’s position on illegal immigration, the first of these might have proven to be the most politically sensitive allegation.

The retraction followed the filing of a complaint, in a Maryland court, against the Daily Mail and another defendant – a blogger who made similar allegations. It appears that the complaint is only in respect of the article’s publication on the Daily Mail’s website, rather than in the print version. However, the retraction appeared online and in the paper.

Libel tourism

Such a claim, by a US citizen against a British publication, raises issues of jurisdiction and it is interesting that the complaint was filed in the US, rather than in the more claimant-friendly jurisdiction of England and Wales. While the Daily Mail is a British newspaper, its website has a significant international readership: the court papers refer to United States web traffic of 2m visitors per day.

But the Daily Mail’s article was most prominently published in England and Wales and it might have been reasonable for Trump to issue proceedings in the High Court. However, recent changes to both English and US law have significantly restricted the ability of claimants to start legal claims outside their own country of residence.

Retraction as it appeared in the Daily Mail, Friday September 2.
Daily Mail

Until fairly recently, English courts were relatively relaxed about “forum shopping” or “libel tourism” in defamation. In cases where the publication took place outside the claimant’s own jurisdiction, English courts were easy to persuade that they should hear the claim. When Liberace was defamed by the Daily Mirror in 1956, he chose to sue in England and Wales – he was entitled to protect his considerable reputation in England. If the Daily Mirror had been available in the United States, then he might have chosen to sue in that country. To a large extent, the decision was up to the claimant.

However, there has never been an unrestricted right for non-residents of England and Wales to bring claims in English courts. In 1937, M. Kroch, a resident of France, who had been defamed in a Belgian newspaper, was refused permission to bring a claim by the Court of Appeal. The report does not explain why M. Kroch wished to sue in England, but it does record that he failed to establish any sort of reputation or connection within the jurisdiction, apart from staying in rented rooms while bringing his claim.

However, as long as the claimant had a reputation within the UK, and the libel had been published – in defamation terms, that the words had been read by a person other than the author or subject of the statement – the courts would grant permission for the case to proceed.

It is fair to say that the bar was very low, both in terms of the claimant’s public profile within England and Wales and the extent to which the statement was published. In the 2005 case of Khalid Salim Bin Mahfouz and others vs Dr Rachel Ehrenfeld, the Saudi businessman sued Ehrenfeld, an American author, for alleging that he had helped to fund terrorism. While the claimant had some connection with England and Wales, Ehrenfeld had none – and the book in question was not published in the UK. However, the first chapter was available online and 23 copies had been sold, via the internet, to buyers in England. This was a sufficient connection with England and Wales for the High Court to allow the claim to proceed. The court found for the plaintiff.

Protecting free speech

The Ehrenfeld case, and other high-profile claims, provoked a strong reaction in the United States – the state of New York enacted the Libel Terrorism Protection Act in 2008 and, in 2010, Congress followed suit with the Securing the Protection of our Enduring and Established Cultural Heritage (SPEECH) Act.

Both these acts prevent American courts from enforcing English (and other jurisdictions’) libel judgments, unless the foreign court provides at least the same level of protection to free speech as American courts. It should be noted that, by treaty or as a matter of international comity, courts will generally enforce international judgments.

On the British side of the pond, the Defamation Act 2013 also tackled the issue of libel tourism – now, where the publisher is not a resident of the UK or other Lugano Convention countries, the court has to be satisfied that England and Wales is “clearly the most appropriate place in which to bring an action”. However, this would not necessarily prevent a non-resident, such as Mrs Trump, from bringing a claim in respect of a publication within England and Wales.

Given the context of the current presidential election campaign and the importance of Melania Trump’s reputation as reflecting on her husband, it is how this will play out with American voters that is important – so it is the coverage in America and the chance to answer those allegations to the American public that matters most. Given this, it would have been difficult to argue that England was the most appropriate place to take action.

The Conversation

Timon Hughes-Davies, Lecturer in Law, University of Exeter

This article was originally published on The Conversation. Read the original article.

Is Katla crying wolf? Icelandic volcano’s rumblings don’t mean airspace chaos is imminent

Physical Geography lecturer, Dr Kate Smith reflects on the 2010 eruption of Icelandic volcano Eyjafjallajökull, and the recent rumblings of its close neighbour Katla.

This post first appeared in The Conversation.Conversation logo

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Kate Smith, University of Exeter

There have been rumblings in Iceland recently.

But given its position in the North Atlantic, this is perhaps no surprise. The location makes the country a notorious volcanic hot spot, regularly hit by seismic activity.

Two recent earthquakes in August 2016 have now led to international reports of imminent eruption risk of Katla volcano. They both occurred within the 9km by 14km central crater – or “caldera” – of the volcano in southern Iceland, and were the two largest earthquakes at the volcano since 1977.

So how worried should we be? Will there be a repeat of the chaos in the skies after an ash cloud drifted over Europe in 2010 caused by an eruption at Eyjafjallajökull, Katla’s close neighbour?

In historic terms, we’ve certainly been waiting for an explosive eruption of Katla, one of Iceland´s most active volcanoes, for quite some time. Lying beneath an icecap up to 700 metres thick, over the last 1,100 years explosive eruptions large enough to melt through the ice have occurred on average every 50 years. The last such eruption was in 1918, and the current pause of 98 years is the longest on record.

Katla in 1918.
wikicommons

In the past earthquakes were felt two to 10 hours before Katla erupted through the ice. Since June, earthquake activity in the caldera has been elevated. The large earthquakes on August 29 marked the peak of this seismicity, followed by a series of more than 100 smaller events, finishing early on August 30.

Meanwhile, the rivers that drain from the ice-capped volcano have been smelling of rotten eggs. This smell comes from hydrogen sulphide (H2S), a volcanic gas found in fluids within the caldera beneath the ice. Unusually high H2S levels near Múlakvísl river have prompted official advice to avoid the immediate area. Changes in levels of volcanic gases around volcanoes and enhanced seismic activity can be signs of increased movement of magma and a future volcanic eruption.

So does all of this physical evidence point to an imminent eruption? Well, probably not. This activity is not actually unusual. Since the 1950s, periods of enhanced seismicity and increased gas pollution have not been followed by explosive eruptions, and there is no sign of swelling of the volcano or harmonic tremor (continuous rhythmic earthquakes) suggesting magma movement.

Earthquake activity at Katla also regularly increases in summer and autumn. As the summer progresses, more glacial ice melts, and small floods can occur. These larger volumes of melt water also increase pore pressure in the crustal rocks and can trigger earthquakes. Changes to water flow can also alter how much geothermal fluid is in the rivers, hence the smell.

Land of fire and ice.
Chmee2/Valtameri, CC BY

In winter the melting reduces and water exists only in small pockets at the base of the ice, which reduces pore pressure in the crust and reduces seismic activity.

After effects

However, volcanoes can change rapidly and in unexpected ways. We can’t say for sure that Katla will not erupt in the near future. A 98-year repose period is long, and twice before eruptions of Katla have followed Eyjafjallajökull in the 1820s and in 1612.

So what would happen if Katla did erupt? Eruptions from this volcano over the last 120,000 years have been varied, but the most likely eruption would be from the central caldera. A very small eruption wouldn’t melt through the ice, but a larger one could melt through explosively. Explosive Katla eruptions typically involve ash clouds and large floods (jökulhlaups) of meltwater, ice and sediment that flow across the surrounding lowlands. Lava is not usually seen since most eruptions are subglacial.

A small explosive eruption from Katla is the most common eruption type and would last from days to a couple of weeks, produce a plume up to 14km high, ash fall in Iceland and a large flood, but would be unlikely to affect anywhere outside of Iceland.

A larger-scale event could last weeks or even months. In this case the plume would be up to 25km in height and could impact air quality and air travel in the UK and Europe within two days if the wind blows ash in that direction. Iceland could expect heavy ashfall, with implications for travel, agriculture and air quality, and a large flood. Such floods can have peak discharges (water flow rates) greater than the Amazon, and cause major landscape change and local tsunamis.

If there is an eruption, both Iceland and the UK should be well prepared. Evacuation plans exist for local communities and information is available in several languages. The UK Meteorological Office monitors ash in the atmosphere and is able to predict what areas could be affected.

Eyjafjallajökull ash cloud of 2010.
PA

When I began studying Katla in 1999 I was told she could erupt any time. This remains true today and with every day that passes, we get closer to an eruption. But I wouldn’t bet on it happening right now.

Icelandic and international scientists work hard to investigate Katla´s past and carry out 24-hour monitoring with sophisticated equipment to understand its present and future. We study volcanic ash, rocks, jökulhlaup deposits, river levels and gas emissions on the ground. Earthquakes and GPS records are analysed remotely and we use satellites and overflights to examine the ground and ice surfaces from the air. An eruption may not be imminent – but it is exciting that we can detect and interpret these clues to assess Katla’s next move.

The Conversation

Kate Smith, Lecturer in Physical Geography, University of Exeter

This article was originally published on The Conversation. Read the original article.

The social life of sea mammals is key to their survival

Biosciences PhD student, Philippa Brakes, looks at the diversity in behaviour of our ‘oceanic cousins’. From the tool using sea otters to the ‘bubble netting’ strategy of the humpback whale.

 This post first appeared in The ConversationConversation logo
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Philippa Brakes, University of Exeter

The beguiling behaviour of marine mammals in their natural environment is fascinating to us human observers. Watching dolphins leap gracefully through the surf, or whales making waves with their massive tale flukes is the stuff of countless bucket lists and high definition wildlife documentaries.

Perhaps part of the appeal lies in marine mammals behaving a lot like we do. They share many of our biological characteristics, such as bearing live young, suckling them with rich fatty milk and investing time and energy into rearing them into adulthood.

Studying their behaviour, what makes them tick as complex social creatures, is essential for their conservation in an aquatic environment which remains almost entirely alien to us. And while it may be alien, it is an environment with a massive human footprint.

For unfortunately mammalian attributes are not all we share with our oceanic cousins. There is arguably now no marine habitat that remains unaffected by human activities. Prey depletion caused by humans, noise, temperature changes, chemical pollution and entanglements in fishing gear have all changed the place in which marine mammals evolved.

Our research shows that this simple reality makes the need to understand their behaviour and social structures all the more urgent, a call which is being echoed by the charity Whale and Dolphin Conservation.

In recent decades there has been a strong emphasis in conservation circles on understanding the population size and distribution of marine mammals, as well as their genetic diversity.

Conservation is principally obsessed with conserving genetic diversity, which is exactly as it should be, as diverse gene pools help ensure resilience against environmental change. But genes may not be the whole story.

Marine mammal behaviour, just like ours, is partially determined by genes and the environment in which they live. However there are also social factors at play, and what makes marine mammals behave the way they do is potentially as complex as the processes which drive human behaviour.

In some cases, nurture may play just as important a role as nature for marine mammals. Almost 20 years ago, renowned conservation biologist Bill Sutherland examined how the behaviour of different species could be used to improve conservation efforts. He concluded that behavioural ecology needed to be better integrated into conservation science and policy making. But to what extent has this message from 1998 been taken on board?

Marine mammals exhibit a wide range of fascinating behaviours, from the complex cooperative bubble-net feeding of humpback whales, to ice-cave building polar bears and tool-using sea otters. They also have a great diversity in their social structures and changing social dynamics, which range between the complex third-order alliances of bottlenose dolphins, close relationships between non-related males, to the more solitary lives of beaked whales.

As well as having innate behaviours, which they acquire through their genes, these species, like humans, can learn individually and from each other. Social learning may be of particular importance to conservation efforts, because it can influence the resilience of a population to changes in their environment.

Killer whales learn foraging strategies from their social group and tend to stick to them. As a result, if there is a decline in their preferred prey, they may be less likely to switch to other species, or use alternative foraging tactics. Such a behaviourally conservative species is likely to be more vulnerable to change.

Survival skills

But learning is only part of marine mammal social dynamics. Social structure, and the various roles played by individuals may also be important for how a population responds to change. The loss of individuals that hold key information on the location of critical habitat or a food source may have significant consequences.

Humans live in many different types of cultures, environments and circumstances. We make important choices about what to eat, who to socialise with, where to live and how many offspring to have. These factors can strongly influence our fertility rates, survival, and even our evolution. It is certainly plausible that many of these factors influence the success of marine mammals as well.

A better understanding of the behavioural ecology of marine mammals is therefore hugely important. It is difficult to envision an approach toward conserving a population of modern humans which merely preserved their genetic integrity and did not also consider their socially learnt behaviour.

While there are some attempts to incorporate behaviour, efforts to conserve marine mammal biodiversity still focus strongly on maintaining genetic integrity and diversity. But the emerging evidence indicates that social and behavioural diversity may also be central to individual, group, and population viability. The challenge ahead is teasing out the most relevant factors and understanding how to incorporate this new knowledge into conservation efforts.

On the whole, policy makers have been slow to keep up with the emerging behavioural research. More alarming still, from the perspective of the marine mammals themselves, is that the degradation of their environment has continued apace.

The Conversation

Philippa Brakes, Post-grad Researcher, University of Exeter

This article was originally published on The Conversation. Read the original article.

Teen obesity caused by going into ‘power-saving mode’

As new research on the subject of teen obesity hits the headlinesProfessor Terry Wilkin – Professor of Endocrinology and Metabolism in University of Exeter Medical School – looks at the evolutionary trait of ‘power-saving’ which may be trapping them.

This post first appeared in The Conversation. Conversation logo

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Terry Wilkin, University of Exeter

It is possible that modern teenagers are trapped by a trait which evolved thousands of years ago to help them through puberty, but which now leaves them vulnerable to obesity.

Adolescents need an extra 20-30% energy every day to fuel the growth and changes in body composition that characterise the six years or so of pubertal development. Energy comes from calories in the food they eat, but how could hunter-gatherers guarantee the extra calories they needed as adolescents when their food supply was limited?

We believe they may have unearthed a strategy that worked well for our ancestors, but which does quite the opposite now.

In our research, we have been monitoring a group of children as they progress through childhood from five to 16 years of age (the EarlyBird study). We found, as expected, that more energy was burnt as children got bigger. However, after the age of ten, the calories they burnt unexpectedly fell, despite the fact that they were growing faster than ever. The amount of calories burnt by age 15 was around 25% lower in both boys and girls. Only at 16 years of age, when the growth spurt was over, did the energy spend begin to increase again.

The study has three important qualities: it is longitudinal (which means that it measures the same group of children throughout), its age spread is very narrow (which means that age-related changes can be more accurately identified), and few people dropped out of the study (important statistically).

In a publication last year, we described two distinct waves of weight gain; one occurring sometime between birth and five years of age, and the other in adolescence. The early wave affected only some children – the offspring of obese parents – while the later wave in adolescence involved children generally.

Poor parental eating habits passed on to their children seemed a likely explanation for early obesity, but we had no good explanation for the later wave of obesity, until now.

Mystery solved?

Energy balance can be thought of as a bank account. Calories are deposited, and calories are spent. Body size (the balance in the account) depends on the difference between the two. So, although the explanation we offer is entirely speculative, and we will never really know because we don’t have the data on our ancestors, the researchers proposed that a downward shift of energy expenditure into “power-saving mode” might help to conserve the calories needed for the growth spurt in puberty.

The energy burnt over 24 hours has two components: voluntary and involuntary. The voluntary component is physical activity, which is easy to understand. What people understand less readily is that the involuntary component is by far the bigger one. Involuntary energy expenditure (so-called resting energy expenditure) is used just to keep alive; to keep the blood temperature at 36.8°C, fuel the brain to think and enable the organs to function.

Involuntary energy expenditure accounts for around 75% of the total calories burnt in a day, which explains why physical activity has a limited impact on obesity. A fall of 25% in resting energy expenditure makes a big hole in the calories burnt each day.

Why does all this matter, and why does it occur? It matters because it makes obesity more difficult to avoid if teenagers are trapped by a long period of low-calorie burn. We don’t know for sure why it occurs, but could speculate that it may be a throw-back to earlier evolutionary times, when calories were scarce but adolescents still needed 25-30% more calories a day to fuel growth and bodily changes.


Not as easy as buying a burger.
Nicolas Primola/Shutterstock.com

How did hunter-gatherers assure the supply of extra calories needed to reach maturity? It is possible that their bodies adapted by switching down its calorie expenditure, so as to divert the calories to the energy needed to grow. Obesity is a recent problem, and the adaptation now works adversely in a world where calories are cheap and readily available in a highly palatable mix of sugary drinks and calorie-dense foods.

The worst outcome is that adolescents and their families take these findings to mean that they can do nothing about teenage obesity. The best is that a new explanation for teenage obesity leads to better understanding, and an avoidance of the foods that are the cause.The Conversation

Terry Wilkin, Professor, University of Exeter

This article was originally published on The Conversation. Read the original article.