A child's first and instinctive reaction to lack of food — that is, to lack of energy intake — is to reduce energy output. And by conserving health and growth at the expense of activity, the child can even maintain a normal appearance. A European child may spend up to two-and-a-half times as much energy on walking and running as a child in a malnourished community in Africa. The reduced activity of the malnourished child comes at an age when play and exploration of the environment is particularly important to the development of physical and mental skills.
In 1984 the average estimated energy output for an African child was 79 units compared with 98 units for a European child (Unit = Kcal/Kg bodyweight/day). One study in Mexico has shown that by the age of three years, a group of malnourished children were already one year behind their well-nourished contemporaries in language development.