The United Nations has urged people to stop eating meat in order to save the planet
Experts urged westerners to become "demi-tarians" by halving the amount of meat they eat.
A report for the UN Environment Programme said that pollution from fertilisers is threatening human health and the environment by causing phenomena such as toxic algal blooms.
It said that 80 per cent of the nitrogen and phosphorus used in fertilisers is consumed by livestock because it is used to grow the crops they eat.
The scientists, led by Professor Mark Sutton of the UK's Centre for Ecology & Hydrology, said eating smaller portions or having meat every other day would help slash pollution.
Europeans eat 35 per cent more protein than recommended by the World Health Organisation while Americans overeat it by 58 per cent - and most of it comes from meat.
Meanwhile regions such as Asia, and particularly, China, are increasingly eating meat as their economies develop.
Professor Mark Sutton, chairman of the International Nitrogen Initiative, said the West needs to set an example to help slow the world's growing reliance on meat.
He said: “To aim towards eating half of the amount of meat we are currently eating is a good starting point.
"We should aim to be demi-tarians - eating half the meat we have typically been eating."
We need to realise that over-eating is not healthy - not for the environment and not for ourselves.”
He added that this switch could reduce the risk of a repeat of the horsemeat scandal which has been triggered by long trans-continental supply chains.
He advocated a more local supply chain which would make it easier to trace where meat came from as well as reducing pollution.
He said: "If we eat meat less often, we might go for a higher quality product when we do."
Co-author Dr Bruna Grazzetti of the Universite Pierre et Marie Curie in Paris, said: "We need to reduce consumption of meat in countries were consumption is excessive compared to recommendations for a healthy diet.
"It does not mean becoming vegetarians but, say, reducing the size of the portions of meat we eat or not eating meat every day."
The report says that humans have "massively altered" the natural flows of nitrogen, phosphorus and other nutrients.
It adds: "While this has had huge benefits for world food and energy production, it has caused a web of water and air pollution that is damaging human health, causing toxic algal blooms, killing fish, threatening sensitive eco-systems and contributing to climate change."
It set out a 10-point plan to reduce the pollution, including using nutrients more efficiently as well as cutting meat consumption.
With 60% of our daily intake of nutrients coming from animal products, experts have warned that pollution will continue to rise unless we stop our over consumption of meat.
The report was backed by Achim Steiner, United Nations Under-Secretary General and Executive Director, who said: “Whether we live in a part of the world with too much or too little nutrients, our daily decisions can make a difference.”
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Sorry, vegans: Eating meat and cooking food is how humans got their big brains
Vegetarian, vegan and raw diets can be healthful, probably far more healthful than the typical American diet. But to call these diets “natural” for humans is a bit of a stretch in terms of evolution, according to two recent studies.
Eating meat and cooking food made us human, the studies suggest, enabling the brains of our prehuman ancestors to grow dramatically over a few million years.
Although this isn’t the first such assertion from archaeologists and evolutionary biologists, the new studies demonstrate that it would have been biologically implausible for humans to evolve such a large brain on a raw, vegan diet and thatmeat-eating was a crucial element of human evolution at least a million years before the dawn of humankind.
Calories to grow our brains
At the core of this research is the understanding that the modern human brain consumes 20 percent of the body’s energy at rest, twice that of other primates. Meat and cooked foods were needed to provide the necessary calorie boost to feed a growing brain.
One study, published last month in the Proceedings of the National Academy of Sciences, examined the brain size of several primates. For the most part, larger bodies have larger brains across species. Yet humans have exceptionally large, neuron-rich brains for our body size, while gorillas — three times as massive as humans — have smaller brains with one-third the neurons. Why?
The answer, it seems, is the gorillas’ raw, vegan diet (devoid of animal protein), which requires hours upon hours of eating to provide enough calories to support their mass.
Researchers from Brazil, led by Suzana Herculano-Houzel, a neuroscientist at the Federal University of Rio de Janeiro, calculated that adding neurons to the primate brain comes at a fixed cost of approximately six calories per billion neurons.
For gorillas to evolve a humanlike brain, they would need an additional 733 calories a day, which would require two more hours of feeding, the authors wrote. A gorilla already spends as much as 80 percent of the tropics’ 12 hours of daylight eating.
Similarly, early humans eating only raw vegetation would have needed to munch for more than nine hours a day to consume enough calories, the researchers calculated. Thus, a raw, vegan diet would have been unlikely, given the danger and other difficulties of gathering so much food.
Cooking makes more foods edible year-round and releases more nutrients and calories from both vegetables and meat, Herculano-Houzel said.
“The bottom line is, it is certainly possible to survive on an exclusively raw diet in our modern day, but it was most likely impossible to survive on an exclusively raw diet when our species appeared,” Herculano-Houzel told LiveScience.
The study puts an upper limit on how big a brain is able to grow while on a premodern raw, vegan diet. But the researchers could not determine when daily cooking began. Was it about 250,000 years ago, when humans were nearly fully evolved with big brains, which is supported by archaeological findings? Or was it about 800,000 years ago, when prehumans began their most dramatic brain-growth spurt, an era for which there is little archaeological evidence of controlled fires for cooking?
Meet the meat-eater
If cooking wasn’t routine before the dawn of modern humans, eating meat certainly was.
The second study, published in October the journal PLoS ONE, examined the remains of a prehuman toddler who died from malnutrition about 1.5 million years ago. Shards of a skull found in modern-day Tanzania reveal that the child had porotic hyperostosis, a type of spongy bone growth associated with low levels of dietary iron and vitamins B9 and B12, the result of a diet lacking animal products in a species that requires them.
The child was around the weaning age. So either the child’s mother’s breast milk lacked key nutrients or the child himself did not consume enough nutrients directly from meat or eggs.
Either way, the finding implies that meat must have been an integral, and not sporadic, element of the prehuman diet more than 1 million years ago, said the study’s lead author, Manuel Dominguez-Rodrigo, an archaeologist at Complutense University in Madrid.
This supports the theory that meat fueled human brain evolution because meat — from arachnids to zebras — was plentiful on the African savanna, where humans evolved, and is the best package of calories, proteins, fats and Vitamin B12 needed for brain growth and maintenance.
“Carnivore animals, whether terrestrial or aquatic, are bigger-brained than herbivores,” Dominguez-Rodrigo told LiveScience. He added that “there is no [traditional] society that live as vegans,” essentially because it wouldn’t be possible to get Vitamin B12, which is only available in animal products.
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