AS MUCH food is wasted in developed countries as is produced in sub-Saharan Africa.

This ''eye-popping'' statistic highlights one of the big changes urgently required to meet the challenge of feeding 9 billion people by 2050, a visiting expert in agriculture and economics has said.

Chris Barrett, of Cornell University, warns there is ''dangerous complacency'' about global food security. Professor Barrett, who will give a public lecture on Wednesday night at the University of Sydney, said that demand for food is about to rise significantly, particularly as a result of population growth in developing countries, rises in income and the migration of people to towns and cities.

There is no magic bullet with which to meet this unprecedented demand, which will be for animal products, processed foods, fruit and vegetables, and traditional staples, he said.

''We need a multipronged strategy to ensure our grandchildren's generations do not confront chronic global food crises of the sort that our grandparents' generations so skilfully averted on our behalf.''

If can be difficult for people in countries like Australia, with an abundance of affordable food, to fully appreciate the looming problem fully but it will eventually affect food prices everywhere if it is not addressed.

''The global food price crises of 2008 and 2011 offered a glimpse of what is to come if we do not act swiftly,'' he said. The requirement for more food would also have environmental consequences, increasing the pressure to convert forests, wetlands and grasslands to crop and livestock production.

As an exporter of food, and a world leader in agricultural research and innovation, Australia has an important role to play in helping feed the world, Professor Barrett said.

Change must occur disproportionately in Asia and Africa, where the extra food was most needed, because food is perishable and expensive to transport, he said. At present, yields in these regions are only a third of those in higher-income nations. Governments and the private sector needed to invest substantially in agricultural productivity to improve the nutritional value of foods, not just the amount of calories, Professor Barrett said. ''One hundred million to 140 million children are deficient in vitamin A. Two billion people are iron deficient, mainly women,'' he said.

The regions where food demand is expected to be the greatest are those that will be worst affected by global warming, yet there has been ''no significant progress on mitigating or adapting to climate change'', he said.

Rich nations could do a lot to reduce their food consumption, reduce food waste and ease the pressure to farm more land.