It warns world leaders some regions would fail in halving the number of hungry by 2015.
In their latest report on food insecurity, the agencies estimated 842 million people were suffering chronic hunger in 2011-13, or 12% of the world's population, down 17% from 1990-92.
The vast majority of people suffering hunger live in developing countries, where the prevalence of undernourishment is estimated at 14.3%, the report found.
Africa remains the region with the highest prevalence of undernourishment, with more than one in five people estimated to be undernourished, while most of the undernourished people are in southern Asia.
The 842m figure was lower than the last estimate of 868m in 2010-12 and 1.02 billion in 2009, but the report said progress in meeting the Millennium Development Goal to halve the prevalence of hunger in the world by 2015 was uneven.
Many countries were unlikely to meet the goal adopted by world leaders at the UN in 2000, said the Food and Agriculture Organisation, the World Food Programme and the International Fund For Agricultural Development.
Their report said: "Those (countries) that have experienced conflict during the past two decades are more likely to have seen significant setbacks in reducing hunger."