The government has committed to giving an extra £375 million to help feed the world's poorest children.
The aid is part of a £2.7billion global agreement aimed at preventing millions of infant deaths - and boosting the chances of millions more, the Department for International Development (Difd) said.
Prime Minister David Cameron, Brazilian vice president Michel Temer and the Children's Investment Fund Foundation president Jamie Cooper-Hohn led a high-level summit in London of developing and developed nations, businesses, scientific and civil society groups - committing them to supporting a historic reduction in "under-nutrition".
Under-nutrition is a chronic lack of nutrients that can result in death, stunted growth and in a lower resistance to illnesses in later life.
It is the biggest underlying cause of death in under fives in the world and is responsible for 8,000 child deaths each day.
It stunts the growth of children, reducing their potential, undermining their adult earnings by up to 10%, and in some countries reducing the size of the economy by 11% as a result, experts said.
The UK committed an additional £375m of core funding and £280m of matched funding from 2013 to 2020.
International Development Secretary Justine Greening said: "Under-nutrition is stopping children and countries from reaching their full potential, accounting for the loss of billions of dollars in productivity.
"A strong and healthy workforce is vital if a country's economy is to prosper. This means business and science taking a lead in fighting for good nutrition because we understand that better nutrition is the smart way to tackle extreme poverty, child mortality and economic underachievement.
"The commitments secured today will help transform the life chances of millions of children and pregnant women by ensuring they get the right nutrition at the right time, securing greater long-term economic growth and prosperity for all."
The participants, who signed a Global Nutrition for Growth deal, committed their countries and organisations by 2020 to:
- improving the nutrition of 500 million pregnant women and young children;
- reducing the number of children under five who are stunted by an additional 20 million;
- saving the lives of at least 1.7 million children by preventing stunting, increasing breastfeeding and better treatment of severe and acute malnutrition.
Among the participants in today's central London summit were two presidents and four prime ministers from Africa, Irish Taoiseach Enda Kenny, philanthropist Bill Gates, former UN Secretary General Kofi Annan and Unilever chief executive Paul Polman.
Donors have today secured new commitments of up to £2.7 billion ($4.15 billion) to tackle under-nutrition up to 2020, £1.9 billion ($2.9 billion) of which is core funding with the remainder secured through matched funding.
Countries that have previously increased nutrition funding, like the US and Canada, today committed themselves to continuing high level funding while others, like the European Union, the World Bank and Ireland, have increased their support substantially, Difd said.