In adults, the brain uses about 20% of our daily carbohydrate intake. In children, this is more like 50%, because of the dramatic increase in brain growth and activity up to 5 years . Carbohydrates provide the main energy supply of the brain, as glucose, that powers the brain.
PEM, as described above, also represents a shortage of energy from carbohydrates, not just protein. Children from 2-3 years of age with PEM have been reported to have problems in how the brain uses carbohydrates, with higher lactic acid, lower blood flow and some carbohydrates converted into fats .