A United Nations summit on the global food crisis called for trade barriers to be reduced and food export bans scrapped to help stop the spread of hunger that threatens nearly one billion people.

“Nothing is more degrading than hunger, especially when man-made,” UN Secretary General Ban Ki-moon told the Rome summit, where the US and Brazil defended biofuel production from charges that it pushes up world food prices.

The head of the UN’s Food and Agriculture Organisation (FAO), hosting the summit, said wealthy nations spent billions of dollars on farm subsidies, excess food consumption and arms.

“The excess consumption by the world’s obese costs $20 billion annually, to which must be added indirect costs of $100 billion resulting from premature death and related diseases,” said FAO Director-General Jacques Diouf, who is from Senegal.

Humanitarian agencies estimate soaring food prices could push as many as 100 million more people into hunger. About 850 million are already going hungry.

Mr Ban estimated the “global price tag” to overcome the food crisis would be $15-20 billion a year and that food supply had to rise 50 per cent by the year 2030 to meet climbing demand.

“Some countries have taken action by limiting exports or by imposing draft controls,” he said, referring to controls slapped on foods in emergency to guarantee domestic supply.

This “distorts markets and forces prices even higher. I call on nations to resist such measures and to immediately release exports designated for humanitarian purposes”.

Aid agencies blame some Asian nations’ export restrictions on rice, for example, for driving up prices which led to riots as far abroad as Haiti in April, toppling the government.

The Rome summit will set the tone on food aid and subsidies for the Group of Eight summit in Japan next month and what is hoped to be the concluding stages of the stalled Doha talks under the World Trade Organisation aimed at reducing trade distortions.

WTO chief Pascal Lamy said a Doha deal “would reduce the trade-distorting subsidies that have stymied the developing world’s production capacity”. Of the 22 countries most affected by the food crisis, “some are amongst the world’s least trade integrated economies in agriculture”, he said in a speech.

Brazilian President Luiz Inacio Lula da Silva said rich nations’ “intolerable protectionism” was the main cause of food inflation while US Agriculture Secretary Ed Schafer focused on export restrictions, blamed for restricting food supplies.

“We ask all countries to allow the free flow of food and the technologies that produce food,” said Mr Schafer.

Britain urged the EU to cool prices by reforming farm policies that cost consumers over €40 billion a year and said trade talks were at a “critical” stage.

“It is unacceptable that rich countries still subsidise farming by $1 billion a day, costing poor farmers in developing countries an estimated $100 billion a year in lost income,” said British International Development Secretary Douglas Alexander.

The cost of major food commodities has doubled over the last couple of years, with rice, corn and wheat at record highs. This has provoked protests and riots in some developing countries where people may spend more than half their income on food.

The OECD sees prices retreating from their current peaks but still up to 50 per cent higher in the coming decade.

Rising fuel prices, as well as making agricultural supplies like seeds and fertilisers more costly, have raised interest in biofuels, blamed by many for competing with food output for grains and oilseed.

The US and Brazil, the world’s biggest producer of ethanol from sugar cane, defended their biofuels industries from such accusations in Rome. “It offends me to see fingers pointed against clean energy from biofuels, fingers soiled with oil and coal,” Mr da Silva told the summit.

The US plans to channel a quarter of its maize crop into ethanol production by 2022 and the European Union plans to get 10 per cent of auto fuel from bio-energy by 2020.

Washington says biofuels account for only three per cent of the total food price rise while Oxfam puts it at 30 per cent.

“The use of sustainable biofuels can increase energy security, foster economic development especially in rural areas and reduce greenhouse gas emissions without weighing heavily on food prices,” said Mr Schafer.

The summit was attended by Zimbabwean President Robert Mugabe and Iranian President Mahmoud Ahmadinejad, both accused by their critics of contributing to food shortages at home.

Washington said Mr Mugabe’s presence could only serve as an example of “what not to do” on food security. A State Department spokesman said his “ruinous policies” had turned Zimbabwe from a food exporter into a net importer with many starving people.

Italian Jews protested against the Iranian leader’s comments that Israel would disappear, chanting “Israel, Israel, Israel” on a hill by the ancient Roman Circus Maximus, near the summit.