Around a third of food produced globally currently goes to waste -- some 1.3 billion tonnes a year according to the Rome-based UN Food and Agriculture Organisation (FAO).
"With just a quarter of that, we could feed the 842 million hungry," said Robert van Otterdijk, an agriculture industry expert at FAO.
Halving the amount of food wasted would mean having to raise world food production by 32 percent to feed the world's population in 2050, instead of the 60 percent currently estimated.
Mathilde Iweins, coordinator of a report on the cost of food waste, said that "the agricultural areas used to produce the food that will never be eaten are as big as Canada and India combined".
But the FAO said focusing on the type of food being consumed was just as important, warning that malnutrition and poorly-balanced diets impose high costs on society -- from towering health care bills to lost productivity.
"One out of every four children in the world under the age of five is stunted," the FAO said in a report.
"This means 165 million children who are so malnourished they will never reach their full physical and cognitive potential," it said.
About two billion people in the world lack vitamins and minerals that are essential for good health while 1.4 billion people are overweight.
Children with stunted growth may be at greater risk of developing obesity problems and related diseases in adulthood in a worrying cycle of malnutrition.
Of those overweight "about one-third are obese and at risk of coronary heart disease, diabetes or other health problems", the FAO said.
The agency said that while wiping out malnutrition worldwide "is a daunting challenge, the return on investment would be high".
"If the global community invested $1.2 billion (888 million euros) per year for five years on reducing micronutrient deficiencies, the results would be better health, fewer child deaths and increased future earnings," it said.
"It would generate annual gains worth $15.3 billion," it added.
The FAO said it was particularly excited by projects aimed at "raising the micronutrient content of staple foods -- either through 'biofortification' or by encouraging the use of varieties with higher nutrient content".
There are hopes that underutilised, nutrient-rich staple crop species might come into fashion, as well as eating insects such as beetles.
With the fight against malnutrition excelling in some countries and lagging behind in others, the FAO gave examples of methods to help improve food systems.
In rural Vietnam, fish-stocked ponds, chickens used as a source of fertiliser and garden-grown crops have reduced child malnutrition and chronic energy deficiency in women of child-bearing age, while raising incomes.
In Ethiopia, a project involving goats has upped milk consumption and incomes by teaching women better goat management and genetically improving the animals.
The FAO insisted however that country-specific projects must be backed up by global efforts to stem waste.
"Getting the most food from every drop of water, plot of land, speck of fertiliser and minute of labour saves resources for the future and makes systems more sustainable," the organisation said.