Anthony Lake, executive director of UNICEF, told Reuters the problem of malnutrition is vastly under-appreciated, largely because poor nutrition is often mistaken for a lack of food.
In reality, he said, malnutrition and its irreversible health consequences also affect relatively well-off countries, such as India where there is plenty of food, but access to it is unequal and nutritional content can be low.
"Under-nutrition, and especially stunting, is one of the least recognised crises for children in the world," Lake said. "It's a horrible thing. These children are condemned."
Stunting is the consequence of under-nutrition in the first 1,000 or so days of a baby's life, including during gestation.
Stunted children learn less in school and are more likely themselves to live in poverty and go on to have children also stunted by poor nutrition. These in turn increase poverty in affected countries and regions, and drive greater gaps between the rich and the poor, Lake said.
"The numbers are phenomenal. In India, for example, about 48 percent of children are stunted, and in Yemen it's almost 60 percent. Just think of the drag on development," Lake said.
"And the key point is that it is absolutely irreversible. You can feed up an underweight child, but with a stunted child, because of the effects on the brain, it has a permanently reduced cognitive capacity by the age of around two years old."