Distinctive aspects of metabolism and nutrition in infancy

Objectives: The effects of genes, the stage of development, and the environment on various metabolic processes in infancy are described. Some themes discussed cross these three boundaries. Conclusions: Certain substances not normally regarded as essential may become conditionally essential if their precursors are limited in the diet or, alternatively, if the processes of conversion are reduced in activity because of abnormal gene function, or developmental immaturity. Diet is a clear environmental influence but, because the nature of the diet is closely related to age, it is a developmental influence as well. Certain nutrients are followed from the diet, via the gut and intermediary metabolism through to individual tissues and the whole body. The relationships of diet, metabolism and brain function have attracted considerable investigation in recent years. In the right environment, with the correct genes, the processes of development will be smooth and without undue metabolic disturbance. Considerable variation can be accommodated within the elasticity of the systems, but some changes may lead to temporary, or even permanent, malfunction.