This letter has been written by the components of the European Milk Bank Association (EMBA) Working Group on Human Milk Fortification in response to a recent paper published by Mathes et al. (BMC Pediatr. 2018 May 8;18(1): 154) with the aim of drawing attention to the importance of the use of a metabolic marker to adapt protein intake in preterm infants. | Letter to the editor: Clarifying some aspects and the terminology of individualized human milk fortification