Prime Minister David Cameron was to call on world powers on Sunday to boost their efforts to tackle malnutrition across the globe.
Taking advantage of the large number of foreign officials gathered in London for the Olympic Games, Cameron was to urge international action to save 25 million children from stunted growth over the next four years.
The "hunger summit" at Downing Street is being co-hosted by Vice President Michel Temer of Brazil, which will host the next Summer Olympics at Rio de Janeiro in 2016.
Olympians including Ethiopian 10,000 metres gold medallist Tirunesh Dibaba and British long jump winner Greg Rutherford have signed an open letter urging Cameron to "fire the starting gun on the biggest ever push against hunger and malnutrition".
"With world leaders gathered in London and the eyes of billions focused on Britain, the Olympics is an incredible opportunity to change the destiny of millions of children round the world," the letter said.
"As athletes, we know how essential nutritious food is for people to flourish physically and mentally.
"Despite an abundance of food worldwide, one person in seven goes to bed hungry every night and it is children who are often hit hardest."
Cameron was set to pledge £120 million on Sunday for research into drought-resistant and vitamin-enhanced crops for Africa and South Asia.
"The figures are shocking," Cameron was expected to say at the conference.
"One in three child deaths are linked to malnutrition. And 171 million children are so malnourished by the age of two that they can never physically recover.
"Even if malnourished children are able to fight off sickness and infection in their earliest years, their bodies and minds never fully develop," he added.
"It is a tragedy for them, and it's a tragedy for their societies they live in. Children who could grow up to become doctors, farmers, engineers and entrepreneurs or great Olympians are left far behind."
Cameron was also due to announce British funding for a joint programme with Switzerland and Ireland helping people in developing countries to hold officials to account over food aid.
Another programme in Kenya will support a mobile texting scheme to allow early warning of "hunger hotspots", so that food supplies can be delivered more quickly, Downing Street added.
World sport stars including Ethiopian runner Haile Gebrselassie and Brazilian footballer Pele were due to attend the summit, along with ministers and international organisations.
The conference comes ahead of the closing ceremony for the London Olympics on Sunday, which will see the Olympic flame extinguished capital and organisers hand over to the Rio 2016 team.