Protein Deficiency and the Brain
It is doubtful if a dietary deficiency specifically of protein occurs in man without an accompanying degree of energy deficiency. The brain is particularly vulnerable to protein-energy malnutrition (PEM) during its growth spurt. Differences in the growth characteristics of different parts of the brain account for differing degrees of vulnerability within the brain.
Delays in cell replication and in the growth and development of structural components, and particularly of the myelin sheath, resulting from PEM during the growth spurt may be irreversible. In man, the effects of PEM on the amount of myelin appear to be proportional to the effects on brain weight. However, the effects on dendritic and synaptic development appear to be greater than the effects on brain weight.
The effects of maternal PEM in rats on brain development in the offspring will be discussed.
In the rat, PEM after the growth spurt affects certain aspects of the metabolism of the brain. In rats given a 3 % casein diet from weaning, the level of histidine was higher, and that of tryptophan lower, than in brains of rats given isoenergetic amounts of a high-protein diet. These differences were correlated with similar differences in the serum levels of these amino acids.
PEM in children is accompanied by evidence of deficiencies in behavioural and mental development. Whether these deficiencies are the direct result of the effects of malnutrition on the brain or to the effects of other factors, such as sensory deprivation, is not known.
KeywordsBrain Stem Myelin Sheath Growth Spurt Cell Replication Brain Weight
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