 Proteins are of the most important macromolecules in living organisms participating in almost all biological processes. Premature infants are forced to adapt to a new extrauterine environment where supply of nutrients, including amino acids, from mother ceases abruptly. Consequently, the aim of neonatologist is the appropriate, quantitatively and qualitatively nutritional support, to promote brain development, achieve normal endocrine and metabolic function, maintain a growth rate similar to the intrauterine one avoiding extrauterine growth restriction during postnatal period and at the same time encouraging the analogue modulation of body composition increased muscle mass, decrease body fat, hydration. 