By Elizabeth Blunt BBC News

The OECD study says donating money is the best way of helping

A study by the Organisation for Economic Co-operation and Development (OECD) found it costs on average 30% more than providing money to buy food.

This can be done either locally or in an appropriate third country.

The USA and EU produce more food than their citizens need. In Africa, meanwhile, children are starving.

Using the surpluses to feed the hungry seems simple good sense.

But this study reveals direct food transfers as slow, cumbersome and expensive - an inefficient way of getting the right food to the right place at the right time.

Cheaper markets

The problem is that food aid is often driven by other considerations, apart from the needs of the hungry.

The big donors, such as the United States, are most generous with food aid when they have big surpluses, and that, by definition, tends to be when there is plenty of food around.

And they give what they have most of, not necessarily what is most needed.

Whether donors are giving free food imports as a form of budgetary support, contributing to poverty relief programmes, or providing emergency famine relief, the overwhelming conclusion is that the most efficient way is nearly always to give cash to buy food from the cheapest source. Countries which are willing to do this, like Britain and Switzerland, get much better value from their aid money.

But most food aid is still tied.

Much of it is given by the United States, and US law requires that a large part of it should be bought from American farmers, processed in the United States, and transported in American ships.