"Severe child food poverty describes children who are surviving on severely deprived diets so they're only consuming two or less food groups," Harriet Torlesse, a lead writer of a new UNICEF report published late Wednesday, told AFP.
"It is shocking in this day and age where we know what needs to be done."
UNICEF recommends that young children eat foods daily from five of eight main groups -- breast milk; grains, roots, tubers and plantains; pulses, nuts and seeds; dairy; meat, poultry and fish; eggs; vitamin A-rich fruits and vegetables; and other fruits and vegetables.
But 440 million children under the age of five living in about 100 low- and middle-income countries are living in food poverty, meaning they do not have access to five food groups each day.
Of those, 181 million are experiencing severe food poverty, eating from at most two food groups.
"Children who consume just two food groups per day -- for example, rice and some milk -- are up to 50 percent more likely to experience severe forms of malnutrition," UNICEF chief Catherine Russell said in a statement accompanying the report.
That malnutrition can lead to emaciation, a state of being abnormally thin that can be fatal.
And even if these children survive and grow up, "they certainly don't thrive. So they do less well at school," Torlesse explained.