Review of the evidence linking protein and energy to mental development.
To examine the evidence as to whether the relationship between undernutrition and poor child development is causal. Selected studies from developing countries were discussed. Observational studies were first considered then experimental studies of preventative and remedial supplementation. The type of functions affected, the presence of sensitive periods and the role of protein and energy versus that of micronutrients were reviewed. Childhood undernutrition is generally associated with concurrent and longer term deficits in cognition, behaviour and motor skills, although the relationship is likely to be confounded by socio-economic factors. Supplementation trials have had many design problems. However, those beginning at any age from pregnancy up to 24 months have consistently had concurrent benefits suggesting a causal relationship. Supplement begun in older children had little or no effect, albeit there are too few studies to conclude with confidence. The limited evidence suggests that benefits are more likely to be sustained if supplementation begins in late pregnancy or at birth and is continued until the child is at least 24 months old. Deficits in cognition tend to be global and there is insufficient evidence of specific deficits. There is some evidence that the first 2 years of life are most sensitive to the effects of undernutrition. Most studies have failed to separate the effects of energy and protein from those of micronutrients. One study showed that energy and/or protein affects children's development. Psychosocial stimulation has had consistent benefits on undernourished children's development. Public health nutrition programmes should include a component in which children who are at risk are targeted during the first 2 years of life with combined interventions involving nutrition, health care and early stimulation.