The United Nations on Monday marked World Food Day to call attention to the 850 million hungry people around the world, almost half of them children who are locked in a cycle of malnutrition and disease.

Led by the Food and Agriculture Organisation (FAO), the theme for this year is investing in agriculture for food security.

The semi-arid Sahel region of West Africa is amongst the most food insecure regions in the world. The highest child mortality rates on the globe are found in the Sahel, and malnutrition is responsible for more than half of those deaths, according to the World Food Programme (WFP).

“You see it particularly at this time of year as the rainy season comes to an end and disease is prevalent with standing water,” said Marcus Prior, WFP public information officer for West Africa.

“Many children around the region struggle to fight off infection, fight off malaria. They are malnourished and their systems are ill-equipped to fight off these kind of illnesses, whereas a healthy child with a more well-balanced diet would be able to throw off many of these illnesses with just a small amount of medication.”

Anna Taylor, head of hunger reduction for Save the Children UK, said the quality of diet, not just the quantity of food, is particularly important for a child’s early development. She said in many developing countries infants start out with breast milk, which is good, but diets then become heavy in carbohydrates.

“Basic things like oil or animal products are almost always in very tiny quantities, if at all, and they might get some green vegetables but most of their energy comes from maize, rice or other carbohydrates,” Taylor said. “It fills the stomach but doesn’t give the minerals and vitamins for growth.”

The consequences are lasting, she said.

“If children get to their second birthday and they’ve not grown to their full potential that stuntedness is carried over into their later years,” Taylor said. “If a child doesn’t get the nutrients it needs it affects the mental development of the child and if a child is malnourished and listless it is harder for the mother to interact with the child, so they get this knock-on effect in terms of development.”

Malnourished children are less capable of fighting off disease, which in turn makes them more malnourished.

“They get into this vicious cycle: they get sick, don’t want to eat, lose weight and it affects their immune system,” Taylor said. “It’s very difficult for them to break out of that.”

WFP says that 37 percent of all children under five years of age in the Sahel are chronically malnourished.