Chronically malnourished children struggle to read and write simple sentences regardless of their level of schooling, according to research by Save the Children.
Eight-year-olds who are stunted by malnutrition are 19% more likely to make a mistake while reading a simple sentence, the report Food for Thought said.
Stunted children are 12.5% more likely to make a mistake writing a simple sentence and do 7% worse on basic maths questions.
The findings, based on research with thousands of children in Ethiopia, India, Peru and Vietnam, come 10 days before a global nutrition summit in London and ahead of this year's G8.
More top news
Man who has barricaded himself in house for three days may have a stash of petrol and other explosives, police say.
Jessica Drake is the 11th woman to allege Donald Trump engaged in inappropriate sexual behaviour.
The singer said he often dreams he is with his late wife - only to wake up and remember his loss again.