Human milk contains numerous immune-protective components that protect the premature infant from sepsis and necrotizing enterocolitis. Because of these protective effects, human milk is the feeding of choice for the premature infant. However, human milk does not provide adequate amounts of most nutrients for premature infants and must therefore be supplemented (fortified) with nutrients. Commercially available fortifiers provide energy and most nutrients in adequate amounts. The exception is protein, which is present in expressed milk in highly variable amounts and which is not provided in sufficient amounts by most fortifiers. Some liquid fortifiers are higher in protein content than powder fortifiers and provide adequate amounts of protein.