The food agency of UN said that obesity and poor nutrition weigh heavily on the global economy and told governments that investing in food health would bring big economic as well as social returns.
Lost productivity and spiralling health care bills linked to obesity cost the world economy around $1.4 trillion a year (1.1 trillion euros), the Food and Agriculture Organisation (FAO) said.
Improving nutrition would boost earnings, "with a benefit-to-cost ratio of almost 13 to 1," it said, adding that some 1.4 billion people in the world are now overweight and a third of them are obese.
The FAO underlined that while there had been some progress in reducing hunger rates around the world, the problem of improving nutrition was still treated as a low priority by many countries.
"We must strive for nothing less than the eradication of hunger and malnutrition," FAO director Jose Graziano da Silva said in a video message at the presentation of the report in Rome.
"The development community is paying more and more attention to malnutrition," he said.
Assistant director general Jomo Sundaram told AFP: "It may be possible to eradicate hunger in the sense of not enough calories, but it is much more difficult to improve nutrition."
In its yearly report, the Rome-based agency found 12.5 percent of the world's population -- or 868 million people -- are still undernourished, while 26 percent of children are stunted by malnutrition.
A rapid rise in obesity is being seen in the associated costs in low- and middle-income countries, it said, pointing out that the highest obesity rates in the world were now in Mexico.
FAO officials said the problem is a complex one and some countries have both under-nourishment and obesity problems, calling for more "dietary diversity" and agricultural systems that are not oriented solely to production of cereals.
"Other nutrient-rich foods like fruit, vegetables, fish, meat and eggs should come into the picture as key items for which productivity should be increased," said Kostas Stamoulis, director of the FAO's agricultural department economics division.
FAO said rising urbanisation, sedentary lifestyles and the increased availability of packaged foods meant policy-makers faced significant challenges in bettering nutrition and reversing obesity.
But "the returns are high," it said.
"Investing in the reduction of micronutrient deficiencies, for example, would result in better health, fewer child deaths and increased future earnings," it said.
The costs of undernutrition are estimated at two-three percent of global GDP, equivalent to $1.4 to $2.1 trillion per year, the FAO said.
The agency urged global leaders to enhance nutrition -- in part through agricultural policies -- and promote behavioural change through education.
"Agricultural research and development priorities must be made more nutrition-sensitive, with a stronger focus on nutrient-dense foods such as fruits, vegetables, legumes and animal-source foods," it said.
Proposals for better agricultural policies on nutrition include changes in production "up to the farm gate", with micronutrient fertilisers, bio-fortified crops and crop and livestock diversification.
Governments could also help consumers through subsidies, targeted food assistance for at-risk groups such as children and the elderly, and better product labelling to help shoppers choose more nutritious food.