As the Olympics draw to a close, there is no doubt that the champions of London 2012 will leave a legacy of achievements that inspires large numbers of young people to fulfil their personal potential.

But for 200 million children in the world, a very different legacy is in prospect. These children are severely malnourished. Their height-for-age is substantially lower than that of the reference point for their national population. In some sub-Saharan African countries the proportion of children who are stunted in this way is as high as 50%. We need a new legacy for these children - one that is a global game-changer.

This Sunday, on the same day as the Olympics closing ceremonies, the UK Prime Minister and the Vice President of Brazil will host a very different type of high-level event, bringing experts together to take action on combatting child stunting and malnutrition around the world.

A disastrous burden

Malnutrition is socially and economically disastrous for children and their societies. Malnourished children are more at risk of contracting illnesses. Stunting, and related conditions, is responsible for over 3.5 million deaths of under-fives a year.

And for those not moved by these statistics alone, malnutrition can impair cognitive function leading to lower educational performance and economic productivity. Where childhood malnutrition is at the most alarming levels, the loss to GDP can be as severe as 2% to 3%.

Most tragic of all, poor nutrition throughout women's lives creates a vicious circle whereby young girls become short women who give birth to smaller children who grow up to be smaller adults. We cannot let this cycle continue.

Opportunities for action

We know - more or less - what works. Breast feeding is crucial, as is complementary feeding. Nutrition-sensitive agricultural development is also key.

Typically mothers wean their infants on conventional staples - rice, maize, bananas and root crops such as sweet potatoes and cassava - in a mash or porridge. For example, Asian mothers commonly wean their infants on rice gruel, feeding them the milky liquid produced by boiling rice. It looks like milk but has few micronutrients.

Children who are deficient in micronutrients, especially zinc, iron and vitamin A., are much more susceptible to diseases, such as night blindness, impaired immune systems and stunted growth, and even death.

While micronutrient supplements and specially designed cereal-legume blend foods are available, they are expensive and often not readily available to the poorest and most vulnerable families.

There are, however, other promising solutions to malnutrition through advances in agricultural research. For instance, it is now possible to breed - using modern conventional methods - staple crops rich in proteins and in micronutrients such as vitamin A, iron and zinc. HarvestPlus has crops available, such as an orange-fleshed sweet potato which contains high-levels of vitamin A.

Complementing such efforts in biofortification are agro-ecological approaches. One example is for rural people to grow round the home - in the backyard - an assortment of crops rich in micronutrients, such as spinach and other leafy vegetables, carrots, lentils, fruits, as well as to care for chickens, goats, ducks, and fish in a fishpond.

Such miniature gardens, often called home gardens, are highly developed in Indonesia where the sheer variety of home produce is astonishing. Yet they can be created almost anywhere in the world. Home gardens can provide the micronutrients essential for pregnant and lactating mothers and for children as they grow older. Here and in the battle against malnutrition generally, women comprise a critical core; as mothers ensuring their children are well fed; as smallholder farmers growing nutritious foods; and as innovators and educators. They must therefore be a key priority for support.

Companies such as Victoria Seeds in Uganda are marketing a variety of vegetable seeds (e.g. okra grown for seed in the Acholi region). DFID and USAID are supporting research on home gardens at the World Vegetable Centre (AVDRC), in Arusha, Tanzania.

Global political leadership

But we need an even more concerted global effort to link these initiatives, and others like them, to deliver progress at scale. To encourage more widespread adoption policymakers need to support targeted education and extension, research into optimal combinations of crops and livestock, as well as the provision of appropriate seeds through local agrodealers and seed companies.

I hope that the UK Prime Minister and other assembled leaders at the Global Hunger Event will make a sustained commitment to continue to focus on combatting malnutrition and stunting into 2013 and beyond. We need commitments that will build on and raise the ambition of existing initiatives such as the Scaling Up Nutrition (SUN) movement and the G8 New Alliance for Food Security and Nutrition, and we also need political leadership that will deliver long-term commitment to this agenda.

While the lasting effects of the London Games will benefit many young people in the years to come, a long-term legacy to tackle child malnutrition would help create a level playing field for every child around the world.

Sir Gordon Conway is Professor of International Development at Imperial College London and Director of Agriculture for Impact. His upcoming book, One Billion Hungry: Can We Feed the World?, will be published on 9th October.

Follow Professor Sir Gordon Conway on Twitter: www.twitter.com/ag4impact