The present invention relates to infant formulas and follow-on formulas containing optimised amino acid profiles, in particular optimised amounts and/or ratios of phenylalanine. The formulas may contain intact proteins, hydrolysed proteins, protein fractions, free amino acids and/or a combination thereof selected based on their ability to provide the formula with an optimised amino acid profile. The present invention also relates to the administration of these formulas to infants in order to achieve balanced growth and/or development, for promoting, assisting or achieving balanced growth or development of the brain of an infant and/or the cognitive function of an infant, and may also assist in preventing or reducing the risk of obesity later in life.