In Davos this April, David Cameron outlined his priorities for the UK's presidency of the G8 this year. He talked about advancing trade, ensuring tax compliance and promoting greater transparency, all with the goal of creating "lasting global prosperity". It's a noble goal – lifting people out of poverty and making corporations accountable for their actions. It's reassuring to see these issues receive international attention.

But there is one obvious issue that is not being talked about, which should be at the top of the G8 agenda: animal agriculture and its contribution to world hunger, environmental degradation and skyrocketing healthcare costs, all of which affect the global economy.

There is more than enough food being grown around the world to feed the entire human population. So why are more than a billion people going hungry? Because instead of feeding starving humans, we funnel huge amounts of crops through the animals we use for food. It takes up to 16 pounds of grain to produce just 1 pound of meat. And an astounding 97 per cent of the world's soya crop goes to farmed animals rather than to hungry people.

We could eliminate the worst cases of world hunger with about 40 million tonnes of food. And it would be easy enough to find: nearly 20 times that amount of grain, 760 million tonnes, is fed to animals on factory farms every single year. Compare this to biofuels, which account for only 100 million tonnes. Tens of thousands of people marched in London on Saturday in support of Enough Food IF, a laudable campaign which highlights biofuels as one of the "bad guys" in the fight to end global hunger – and yet, inexplicably, it doesn't have animal agriculture as one of its key themes.

By cutting our meat consumption and slowing the rate at which animals are bred, we could redirect the crops that they would have consumed to the people who need them most. That's why the prestigious Worldwatch Institute maintains that "[m]eat consumption is an inefficient use of grain – the grain is used more efficiently when consumed directly by humans. Continued growth in meat output is dependent on feeding grain to animals, creating competition for grain between affluent meat-eaters and the world's poor". Therefore, raising animals for meat creates a disturbing social-justice issue.

And as meat-based diets spread to developing countries, subsistence farmers are being driven off their land. Efficient, plant-based agricultural models are being replaced by intensive animal agriculture, which also pollutes the air and water and leads to desertification that renders the once-fertile land barren.

The United Nations reports that the meat industry is "one of the top two or three most significant contributors to the most serious environmental problems, at every scale from local to global". And it's easy to see why. Carbon dioxide, methane and nitrous oxide are the principal agents of climate change – and raising animals for food is one of the largest sources of carbon dioxide and the largest source of both methane and nitrous-oxide emissions. When you add up all the energy-intensive stages of raising animals for food, slaughtering them and processing and storing their flesh, it's clear why producing 1 calorie of animal protein requires more than 11 times as much fossil fuel as producing 1 calorie of plant protein. In addition, Greenpeace estimates that in a single crop season, more than 2.9 million acres of the Amazon rain forest in Brazil are destroyed to make more room to grow crops to feed farmed animals.

The water footprint of the livestock sector is also huge. It takes more than 2,400 gallons of water to produce 1 pound of meat, while growing 1 pound of wheat requires only 25 gallons. You save more water by not eating a pound of meat than you do by not showering for six months!

Not surprisingly, the United Nations Environment Programme concluded that "[a] substantial reduction of impacts would only be possible with a substantial worldwide diet change, away from animal products".

Environmental issues, in turn, have a serious impact on our economy. Heat waves, droughts, rising sea levels and other problems caused by climate change can ruin crops and result in increased food prices. Major storms, a developing trend that scientists have also linked to environmental destruction, often do billions of pounds in damage. Sir Nicholas Stern, author of the government-commissioned review on climate change, which has been the reference work for politicians and journalists throughout the last 10 years, warns that if we do not reduce greenhouse-gas emissions, it will take less than 40 years for climate change to cause up to a 20 per cent drop in the world's gross domestic product. He fears that it could be "market failure on the greatest scale the world has seen".

Then there are the skyrocketing healthcare costs that are attributable in large part to the increase in human consumption of meat, eggs and dairy products. Loaded with artery-clogging cholesterol and saturated fat, these products have been linked to cancer, heart attacks, strokes, diabetes and obesity. These top killers burden the National Health Service and necessitate that billions of pounds be spent searching for cures and medications to relieve disease symptoms. They also claim a huge number of lives.

Aside from their environmental and health impacts, the meat, dairy and egg industries cause immense suffering to more than a billion animals every year in the UK alone, most of whom spend their entire lives crammed inside dark, filthy sheds. They don't get to breathe fresh air until they are on their way to the abattoir, where many have their throats slit while they are still conscious.

"Lasting global prosperity" can be attained only through sustainable growth – otherwise, we will simply compound current environmental and economic problems. World leaders at the G8 Summit must take into account the devastating impact of animal agriculture in order to encourage global food changes that will be the catalyst for such growth.