Between 1990 and 2005 the proportion of children under five who were underweight declined by one fifth. But that progress is now under threat. Rising food prices mean that malnutrition and starvation once again threaten many of those at the bottom of the world's economic ladder. While recent spikes in prices are unlikely to be permanent, producers should stop wasting food by subsidising biofuels and give the World Food Programme the funds it needs to distribute calories to those who cannot cope by themselves.

International market prices for wheat, corn, soyabeans and dozens of other commodities have doubled or trebled in recent years. The result is poverty - for millions, a doubling of food prices means destitution - and increased malnutrition. World Food Programme officials have told the Financial Times that the agency may have to cut food rations, or even the number of people it reaches, unless donors provide more cash to pay higher prices.

Some factors affecting prices for the world's poor are clearly temporary. Bad US and EU harvests in recent years, plus drought in Australia, have reduced grain stocks. There has also been a particular squeeze on internationally trade-able oils and grains, as producers such as Russia introduced export quotas in order to control prices at home. Finally, record shipping rates have made food yet more expensive in the poorer, importing countries that need to buy it most.

Other factors suggest a more permanent change. Food production consumes energy - for machinery, for transportation and most of all to manufacture fertiliser - and if oil prices remain high it will have a lasting effect on food.

Cuts to food production subsidies, most notably in the EU, will also have a permanent effect on supply.

But the biggest structural change is biofuels. In the space of a few years, the US has diverted about 40m tonnes of maize to produce bioethanol - about 4 per cent of global production of coarse grains. That rapid growth is largely the result of subsidies - which must halt. The environmental benefits of maize biofuel are ambiguous at best and it should not be favoured over growing maize for food.

These fundamental pressures, however, should not cause despair. Twenty years ago there were warnings that economic growth in China and India, and consequent increases in calorie intake, would lead to devastating food shortages. So far China has been able to supply its population's shift to eating meat.

There are serious challenges to increasing food production: limits to available land, soil degradation and access to water among them. But not only are new technologies such as genetic modification adding to output, there is scope to raise productivity in areas such as the former Soviet Union toward the levels of the most productive farmers.

Over the next few years, therefore, prices should stabilise as supply increases and stocks are rebuilt. In the meantime, those governments that are subsidising biofuels need to cough up and help fund the World Food Programme. The world has enough food to feed everybody - if there is the will to do so.