A third of child deaths globally are caused by poor nutrition, experts warn.
Breastfeeding is key for baby nutrition
Around 3.5 million children die every year because of lack of food or poor quality food, a problem which starts in the womb, studies show.
Yet 25% of these deaths could be prevented with simple steps such as breastfeeding and vitamin A supplements, the Lancet reports.
The majority of undernourished children and pregnant women live in just 20 countries across Africa and Asia.
A special series in The Lancet also reported that poor nutrition in infancy leads to irreversible damage in later life.
Children who are under-nourished are likely to have shorter height and do less well at school, reducing their economic potential and perpetuating the poverty cycle, analysis found.
A separate study found "convincing evidence" for several measures which could have a big impact on reducing deaths if implemented properly.
Zinc and vitamin A supplements as well as encouraging women to breastfeed for at least six months would cut deaths and the loss of years through disability by a quarter, the researchers concluded.
But the international response to child deaths from poor nutrition has been "fragmented and dysfunctional", experts warned.
Some children die because they simply do not have enough food.
But the issue is more complex for other children who suffer stunted growth and illnesses associated with deficiencies of vital vitamins and minerals.
The problem can be exacerbated by poor sanitation which spreads infectious diseases that cause diarrhoea.
Professor Zulfiqar Bhutta, Department of Paediatrics and Child Health at Aga Khan University in Pakistan estimated that 1.4 million child deaths annually are caused by a lack of breastfeeding.
In Africa, Asia, Latin America and the Caribbean less than a third of children under the age of six months are breastfed exclusively, he said.
Professor Caroline Fall, from the University of Southampton, who carried out the research into long-term effects of poor nutrition said: "Having an undernourished mother or infant causes irreversible damage even if nutrition improves later in childhood - you don't get the chance to recover much".
Dr Bruce Cogill, a nutrition expert at Unicef, said the global burden caused by under-nutrition was "a call to action".
He added that nutrition programmes were "woefully under-resourced" compared to other global health issues, such as Aids.
Professor Simon Cousens, from the London School of Hygiene and Tropical Medicine said the period from conception until 24 months of age was most crucial.
"Countries with a high prevalence of under-nutrition must decide which interventions should be given the highest priority, and ensure their active implementation."
Save the Children said if trends in Africa continued, 3.7 million more children will be suffering from malnutrition in 2015 than today.
David Mepham, director of policy at the charity said: "Children who are malnourished suffer cognitive impairment, affecting their capacity to learn, and they have much weaker immune systems, making them more vulnerable to disease and early death."
He called for the UK and EU governments to do more to tackle the problem.