UN food agencies say persistent food crises are leaving 166 million people in 22 countries chronically hungry.

Wars, natural disasters and poor government institutions have contributed to a continuous state of undernourishment in countries such as Afghanistan, Haiti, Iraq, Somalia and Sudan, the Food and Agriculture Operation and the World Food Program said in a new report.

A country that reports a food crisis for at least eight years and receives more than 10 per cent of its foreign assistance as humanitarian relief is considered to be in a protracted food crisis, the two agencies said — offering the first definition of the term in hopes of improving aid response to these nations.

"Protracted crises can become a self-perpetuating vicious cycle," said a report by the two agencies. "Recovery may become progressively more difficult over time."

Among the 22 nations, the proportion of people who are undernourished is almost three times as high as in other developing countries.

UN officials say that 1,800 calories per day is considered the minimum energy intake on average. Anyone regularly without that intake would be considered undernourished, or "chronically hungry."

Countries in protracted crisis require targeted assistance, with the focus not only on emergency relief but also on longer-term tools, such as providing school meals or implementing food-for-work programs, the report said.

Stimulating markets is also an effective long-term measure, the report said, for example through the purchase of food aid from local suppliers.

Currently, most of the assistance to these countries is in the form of emergency humanitarian aid. In Somalia, for example, it is as high as 64 per cent. But globally, only about 10 per cent of assistance to vulnerable nations goes into immediate humanitarian aid, while the rest is aimed at improving productive capacity.

"There is an urgent need for assistance in protracted crises to protect livelihoods as well as lives, because this will help put the country on a constructive path to recovery," wrote the two agency directors, Jacques Diouf of the FAO and Josette Sheeran of the WFP.

The FAO said last month that the number of hungry people worldwide had dropped below one billion to an estimated 925 million people.