Optimal growth, development, and functional maturation of the infant and child clearly depend on the provision of an adequate intake and balance of more than 50 essential macro- and micro-nutrients. Of all these, protein is by far the most important determinant. Protein in the diet provides the essential amino acids necessary for protein synthesis and thus not only protein quantity but also quality is important. However, protein cannot be considered alone since there is a close interrelation between protein and energy metabolism with reference to growth.