Growth restriction, whether it occurs in utero (intrauterine growth restriction) or postnatally, leads to a deficit in lean body mass. Recovery of the deficit in lean body mass, i.e., catch-up growth, is associated with long-term benefits in cognition, but may also be associated with long-term adverse effects on cardiovascular and metabolic health. It is presumed that only catchup of lean body mass is required for benefits in cognition to accrue, whereas recovery of fat mass is optional. Since catchup growth involves recovery of a deficit in lean body mass, it requires increased retention of protein, which in turn requires an increased intake of protein.These high protein needs are difficult to meet with the usual feedings for preterm infants, unless special measures are taken to increase the protein content, i.e., to increase the protein/energy ratio. Without the requisite protein intake, catch-up growth is not possible or will be delayed or be partial, all of which are likely to compromise the realization of the long-term cognitive benefits that result from catch-up growth.