It has also emerged that various constituents of breast milk, including oxytocin, support the development of neurons in the gut. This might explain why premature babies who are not breastfed are at higher risk of developing diarrhoea and necrotising enterocolitis, in which portions of the bowel become inflamed and die.
Serotonin is also crucial for the proper development of the ENS where, among its many roles, it acts as a growth factor. Serotonin-producing cells develop early on in the ENS, and if this development is affected, the second brain cannot form properly, as Gershon has shown in mutated mice. He believes that a gut infection or extreme stress in a child’s earliest years may have the same effect, and that later in life this could lead to irritable bowel syndrome, a condition characterised by chronic abdominal pain with frequent diarrhoea or constipation that is often accompanied by depression. The idea that irritable bowel syndrome can be caused by the degeneration of neurons in the ENS is lent weight by recent research revealing that 87 out of 100 people with the condition had antibodies in their circulation that were attacking and killing neurons in the gut.
A growing realisation that the nervous system in our gut is not just responsible for digestion is partly fuelled by discoveries that this ‘second brain’ is implicated in a wide variety of brain disorders.
In Parkinson’s disease, for example, the problems with movement and muscle control are caused by a loss of dopamine-producing cells in the brain. However, Heiko Braak at the University of Frankfurt, Germany, has found that the protein clumps that do the damage, called Lewy bodies, also show up in dopamine-producing neurons in the gut. In fact, judging by the distribution of Lewy bodies in people who died of Parkinson’s, Braak thinks it actually starts in the gut, as the result of an environmental trigger such as a virus, and then spreads to the brain via the vagus nerve.
Likewise, the characteristic plaques or tangles found in the brains of people with Alzheimer’s are present in neurons in their guts too. And people with autism are prone to gastrointestinal problems, which are thought to be caused by the same genetic mutation that affects neurons in the brain.
Although we are only just beginning to understand the interactions between the two brains, already the gut offers a window into the pathology of the brain, says Pankaj Pasricha at Johns Hopkins University in Baltimore, Maryland. ‘We can theoretically use gut biopsies to make early diagnoses, as well as to monitor response to treatments.’
Cells in the second brain could even be used as a treatment themselves. One experimental intervention for neurodegenerative diseases involves transplanting neural stem cells into the brain to replenish lost neurons. Harvesting these cells from the brain or spinal cord is not easy, but now neural stem cells have been found in the gut of human adults. These could, in theory, be harvested using a simple endoscopic gut biopsy, providing a ready source of neural stem cells. Indeed, Pasricha’s team is now planning to use them to treat diseases including Parkinson’s.
If nothing else, the discovery that problems with the ENS are implicated in all sorts of conditions means the second brain deserves a lot more recognition than it has had in the past. ‘Its aberrations are responsible for a lot of suffering,’ says Pasricha. He believes that a better understanding of the second brain could pay huge dividends in our efforts to control all sorts of conditions, from obesity and diabetes to problems normally associated with the brain such as Alzheimer’s and Parkinson’s. Yet the number of researchers investigating the second brain remains small. ‘Given its potential, it’s astonishing how little attention has been paid to it,’ says Pasricha.
Brain power
Organs
The carnivore’s (ongoing) dilemma
Åsa Wahlquist
When News Limited began its 1 Degree program, which aimed to make the company carbon neutral, it invited employees to submit the steps they would take to reduce their own personal greenhouse gas emissions. In response, a number of News employees offered to reduce the amount of red meat in their diets, or even cut out eating meat altogether.
In that choice, they joined such eminences as Britain’s Lord Stern, the Nobel-winning Rajendra Pachauri of the Intergovernmental Panel on Climate Change, and the vegetarian Sir Paul McCartney who popularised the phrase: less meat = less heat.
Popular wisdom has it that industrial livestock production is killing the environment. But while there are some sound reasons to eat less meat or even become a vegetarian, doing it to save the planet is not necessarily one of them.
We can look at it this way: red meat comes from cattle and sheep, which play a vital role in utilising grasslands, the 60 per cent of the world’s farmland unfit for any other agriculture. When the world’s population of hungry people is rapidly growing, you have to ask whether we can ethically refuse to produce food from so much land.
We could also consider the fact that, on mixed farms – those that run livestock and grow crops – the animals play a critical role in eating farm waste and providing natural fertiliser. If human diets shift towards more legumes, such as soybeans, that will mean more cropping and the accompanying need for more irrigation and higher inputs of nitrogenous fertilisers, which pose their own serious greenhouse gas emission problem (more on this later).
As the implications of people swapping meat for vegetables are totted up, there are signs that the greenhouse gas debate is changing.
In his book, Meat: A benign extravagance, Simon Fairlie, a British journalist and farmer, makes a strong case for sustainable, small-scale farming that incorporates livestock. So persuasive is his argument that Fairlie’s book famously convinced well-known environment writer George Monbiot that his pro-vegan stance was wrong.
The case for meat is not helped by the fact that two of the earliest, most influential and most frequently quoted contributions to the debate are wrong. First was the Food and Agriculture Organisation’s report Livestock’s Long Shadow, which claimed 18 per cent of global greenhouse gas emissions come from livestock. More recently, the International Panel for Climate Change put livestock greenhouse gas emissions at 5.4 per cent of global emissions.
The other highly quotable early entrant was US researcher David Pimentel’s claim that it takes 100 000 litres of water to produce 1 kilogram of beef.
However the Water Footprint Network estimates a global average water footprint of 15 400 litres of water per kilogram of beef. Beef grown on Australian farms seems to require less again, with research by a team including Brad Ridoutt from the CSIRO estimating water use at 6.6 to 440 litres per kilogram.
Ridoutt explains: ‘When people use these figures of 100 000 or even 15 000 [litres of water] these numbers go out into the public domain. The information is not given about what these numbers mean. It just becomes a source of misinformation that can be used in quite a scandalous way’.
Ridoutt is working with the International Organisation for Standardisation to set up a rigorous system, similar to carbon footprinting, that would give comparable figures for water usage by all kinds of agriculture and other human pursuits. ‘The underlying question is to what extent is producing this product contributing to a reduction in fresh water that is available for the environment or for others to use.’
Fairlie ridiculed Pimentel’s figure, citing the case of Bramley, an Angus/Jersey-cross steer he raised. He estimated that if the figure of 100 000 litres per kilogram was correct, young Bramley would have had to consume about 25 000 litres of water a day.
What makes all this so difficult to precisely calculate is that we’re talking about animals, not machines. Farmed animals are biological individuals with different constitutions and diets, living in different geographies, bred and used for different purposes, playing different roles in different farm systems. The result is huge variability in the productivity and resource consumption of livestock around the world: for example, beef produced in Africa in a Sahelian pastoral system – where cattle are used for transport, and ownership is an indicator of wealth – has the lowest carbon fo
otprint at 8.4 kilos of greenhouse gases per kilogram of meat; whereas beef produced in Japan, from the world’s most pampered cattle, has the highest value at 26 kilos of greenhouse gases per kilogram of meat.
Livestock’s Long Shadow has cast its own long shadow over the livestock carbon dioxide emissions debate. Richard Eckard, associate professor with the Melbourne School of Land and Environment, along with many other scientists, disputes the report’s claim that livestock contributes 18 per cent of the world’s emissions, as it counts both cattle not raised for consumption and land not in fact used for livestock.
Eckard and fellow scientists say Livestock’s Long Shadow overestimated how much of the land clearing in the Amazon was for livestock – when up to 40 per cent is cropped with soybeans. Eckard adds: ‘You have all the cattle in India for religious reasons, the cattle in Africa used for transport and wealth generation – a lot do not get consumed’.
Deforestation figures highly in Livestock’s Long Shadow’s sums, but Eckard points out much of Australia’s rangelands were never cleared. ‘All the northern rangelands, they weren’t cleared, they were just stocked with cattle,’ he says. In fact, most clearing, in Australia, has been for cropping.
Ross Garnaut’s Climate Change Review, updated in 2011, reported that although greenhouse gas emissions from livestock accounted for about 10 per cent of Australia’s total, those emissions have declined by 13 per cent since 1990, largely because of a fall in sheep numbers – which dropped from 174 to 74 million. He pointed out that commercially motivated improvements in animal husbandry have ‘incidentally reduced emissions per unit of output. These developments could go further’.
The former chief of CSIRO Livestock Industries, Alan Bell, estimates beef cattle account for up to seven per cent of Australia’s greenhouse gas emissions. And that figure is set to fall. Townsville-based CSIRO scientist Ed Charmley says recent work shows cattle in the northern rangelands are producing 20 to 30 per cent less methane than previous estimates. With about half the nation’s cattle in the north, this means a significant downward revision.
Most of the world’s livestock consume grass. Ruminant animals, such as cows and sheep, possess a special stomach or rumen which contains microbes that can digest grass – and a byproduct of that digestion is the greenhouse gas, methane. This means ruminants produce protein from plants in areas that are unsuitable for any other agricultural activity.
Grasslands occur on land where the soil is too poor, the rainfall too low or the topography too rough for the land to be ploughed and planted with crops.
And before there were modern cattle there were wild ruminants, including the great bison herds of the US prairies and the wildebeest of the African savanna, which had adapted to these grassy regions.
George Seddon has argued the main herbivores in Australia were termites, which, interestingly, also produce methane. Eckard says that in the Northern Territory ‘it is quite feasible that termites are producing more methane on an area basis than livestock’.
Australia also has kangaroos, which, unusually among the large herbivorous animals, are not ruminants, and produce significantly less methane than cows, for example.
Methane, or CH4, is a potent, if short-lived greenhouse gas. It is given a global warming potential rating of 25 times that of carbon dioxide. Methane is the main component of natural gas and coal seam gas. It is also produced from landfill, but the largest source of methane is wetlands.
Eckard explains the quantity of methane a ruminant produces is affected by its diet – a poor diet results in higher methane production – and by genetics. He says there can be a 15 per cent difference in methane emissions within one herd, determined by these two factors.
The steak-versus-lentils argument is further complicated by the fact that grasslands have been found to play another important role in keeping our atmosphere in balance: that is, they sequester, or fix, carbon that would otherwise be released into the atmosphere.
Helen King, former deputy director of the Co-operative Research Centre for Greenhouse Gas Accounting, says:‘There is a lot of research that [indicates] if areas [of grassland] are not grazed, or are not managed, they actually take up less carbon, so grazing animals play a very active role in the carbon cycle. Wellmanaged grass-fed beef is a totally different proposition to growing grains to feed animals or growing grains for consumption’.
If people were to abandon eating red meat, some grasslands, like the Serengeti, might be repopulated by wild ruminants. But the more likely fate of Australia’s grasslands would be consumption by fire. Bushfires, on average, burn over 500 000 square kilometres of Australia annually, mainly the grasslands in the northern half of the country. Bushfire accounts for about 3 per cent of the nation’s net greenhouse gas emissions.
One of the charges made against livestock in general is that it consumes grains that would otherwise be used to feed people. But in Australia, livestock is largely fed grain and oilseed products that would not be used for human consumption.
Feeding grain to cattle doesn’t bring great returns in the desired generation of protein: cattle require 8 to 10 kilograms of grain to produce 1 kilogram of meat. Pigs, on the other hand, require 3 kilograms of feed and chicken requires just 1.7 kilograms of grain to produce 1 kilogram of meat.
Australians are eating less red meat, anyway. Beef consumption has more than halved since 1977, to 31.7 kilos per person. Over the same period, consumption of chicken meat has rocketed from 15 to 45.2 kilos per person. The great Aussie barbecue has paled significantly, which is, on one level, in step with our aims of greenhouse gas reduction.
Every kilogram of beef produces 24 kilos of greenhouse gases. Pork and chicken (both products of non-ruminants) generate much less, at 4.1 and 0.8 kilos respectively.
And yet, ‘People say ruminants produce methane and are less efficient than pigs and poultry, but think about all that grain that we need to produce protein from pigs and poultry,’ Bell says. The argument has moved from red meat to meat and poultry generally.
Even Australian cattle don’t spend their whole lives on grass; at any time, only about 2 per cent of the herd is in feedlots, being fed grain. Bell says feedlots are ‘a tough one for the environmentalists, particularly around methane’. Many environmentalists oppose feedlotting due to its intensive nature and the high-grain diet. But feedlot cattle grow more quickly than grass-fed cattle, and that means they emit less greenhouse gas before they’re slaughtered for their meat. As a result, Australian grain-fed cattle are estimated to produce 38 per cent fewer greenhouse gas emissions than those raised on grass. They emit less again if they are administered Hormone Growth Promotants. In another context this would sound unpalatable, but here it makes sense.
Tara Garnett, from the Food Climate Research Network, at the University of Surrey in the UK, argues that if people didn’t eat livestock, fewer cereal crops would be needed for livestock, but more would be required for humans.
Garnett also estimates that Britons throw out between 18 and 20 million tonnes of food a year. Australians are estimated to waste four million tonnes a year. Once, that food waste went to the pigs and poultry that were an integral part of farms and households – now it is simply wasted.
Animal products supply a third of all the world’s protein. If we eliminated livestock we would have to produce half as much again vegetable protein crops to replace meat.
But in Australia the shift from pasture to crop land results in a reduction in soil carbon. Increasing soil carbon will be critical to Australia’s future carbon balance. And the most effective way to increase carbon levels in soil used for agriculture is to return crop land to well-managed pasture, preferably native pasture.
And there’s another problem. Crops need nitrogen, most of which come from synthetic nitrogen fertiliser. Making nitrogen fertiliser is a very energy-intensive process, using at least 1 to 2 per cent of the world’s energy supply. Then the fertiliser, once applied to crops, breaks down to become the potent greenh
ouse gas nitrous oxide, which has a global warming potential (GWP) of 298. The base unit for GWP is carbon dioxide, which is given a value of one at 20, 100 and 500 years. Methane has a GWP at 100 years of 25. There are other minor contributors, but carbon dioxide, methane and nitrous oxide are the three main greenhouse gases.
Organic farms fix nitrogen in the soil, naturally increasing its fertility through growing legume crops. And this lowers their productivity, because on a stockless farm, around one-third of fields are taken out of grain production for natural nitrogen fixing at any given time.
And here is the next conundrum for the environmentalist.
Garnett says that research into organic farms finds that, on the one hand, they are less energy intensive than conventional farming, but they are also less productive, so organic livestock is more greenhouse-gas intensive.
Bell hesitates to put a figure on the productivity of Australian organic farming, but says, ‘All the data I have seen, more from North America than here, says that organic is always going to be less efficient’.
Can you absorb another complication? Because … there’s the issue of what it takes to produce meat substitutes.
A study by Cranfield University, commissioned by the environmental group World Wildlife Fund, reported that many meat substitutes consumed in Britain are produced from soy, chickpeas and lentils that are grown overseas and imported. A switch to these substitutes would result in more foreign land being cultivated, and raise the risk of forests being destroyed to create farmland. It also found meat substitutes tended to be highly processed and involved energy-intensive production methods.
One of the study’s authors, Donal Murphy-Bokern, said: ‘For some people, tofu and other meat substitutes symbolise environmental friendliness, but they are not necessarily the badge of merit people claim’.
The Best Australian Science Writing 2013 Page 23