The UN's food agency revised down the number of the world's hungry on Tuesday to just under 870 million but slammed the figure as "unacceptable" and warned that the fight against hunger was slowing down.

"With almost 870 million people chronically undernourished in 2010-2012, the number of hungry people in the world remains unacceptably high," the Food and Agricultural Organisation (FAO) said in its 2012 report on food insecurity.

One in eight people around the world are still going hungry, it said.

"In today's world of unprecedented technical and economic opportunities, we find it entirely unacceptable that more than 100 million children under five are underweight," FAO head Jose Graziano da Silva was quoted as saying.

The Rome-based food agency, which compiled the report along with the World Food Programme (WFP) and International Fund for Agricultural development (IFAD), said the number of hungry was down from 925 million in 2010.

The figure is well under the one billion barrier crossed in 2009.

New methods for estimating hunger levels also showed that progress against hunger in the past two decades was "better than previously believed," it said.

"Most of the progress, however, was achieved before 2007-08. Since then, global progress in reducing hunger has slowed," and must rally again to meet the Millennium Development Goal of halving the world's hungry by 2015, it said.

The slowdown is due to multiple factors, including "the global economic crisis, rising food prices, the growing demand for bio-fuels, food speculation and climate change," said Jomo Sundaram, FAO assistant director-general.

The vast majority of the world's hungry -- 852 million -- live in developing countries, where hunger affects 14.9 percent of the population. Most sufferers live in South and East Asia and Sub-Saharan Africa, the report said.

While hunger rates were down annually over the past 20 years, the FAO warned that "considerable differences among regions and individual countries remains."

The numbers of undernourished people has dropped sharply in East Asia, for example, down from 261 million people in 1990-1992 to 176 million in 2010-2012.

But in Sub-Saharan Africa, the figures in the same period have shot up from 170 million to 234 million, the report said.

The latest figures are based on new estimates of the proportion of hungry people in the world after the FAO updated its methodology, Sundaram said, adding that the figures for the past 20 years had been revised.

Figures will from now on be collated over three year periods, he said.

"We note with particular concern that the recovery of the world economy from the recent global financial crisis remains fragile," said Graziano da Silva.

However, despite the warnings of a slowdown in beating hunger, the report said the damage done by the crisis was not as bad as had been expected.

"The increase in hunger during 2007-2010, the period characterized by food price and economic crises, was less severe than previously estimated," it said.

The knock-on effect of "economic shocks to many developing countries" from the struggling West in particular "was less pronounced than initially thought."

"Recent GDP estimates suggest that the 'great recession' of 2008-09 resulted in only a mild slowdown in many developing countries, and increases in domestic staple food prices were very small in China, India and Indonesia," it added.

Boosting the lagging fight against hunger will rely on "strong economic growth," which leads to greater dietary diversity as salaries rise, as well as government action, including financing public nutrition and health programmes.

"Growth alone is unlikely to make a significant impact on hunger reduction.

"In order to reduce undernourishment as rapidly as possible, growth must not only benefit the poor, but must also be nutrition-sensitive," the FAO said.

"Improving food security and nutrition is about more than just increasing the quantity of energy intake -- it is also about improving the quality of food in terms of dietary diversity, nutrient content and safety," it added.

[Image via Agence France-Presse]