The UN's Food and Agriculture Organisation (FAO) said the figure was a record high.
Persistently high food prices have also contributed to the hunger crisis.
The director general of the FAO said the level of hunger, one-sixth of the world's population, posed a "serious risk" to world peace and security.
The UN said almost all of the world's undernourished live in developing countries, with the most, some 642 million people, living in the Asia-Pacific region.
In sub-Saharan Africa, the next worst-hit region, the figure stands at 265 million.
Just 15 million people are left hungry in the developed world. ...