The United Nations has urged people to stop eating meat in order to save the planet

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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.”