Body composition assessment of preterm infants: is it time to switch from research to bedside?

Postnatal growth is closely linked to health outcomes through the so-called developmental programming.¹ Longitudinal assessment of growth is critical to monitor the nutritional status and derive personalized dietary interventions in preterm and low birth weight infants. A comprehensive approach, however, should include not only the standard measurements of anthropometrics but also the assessment of changes in body composition that contribute to the modulation of long-term outcomes.² In light of this evidence, efforts have been made to implement growth and body composition assessments, aimed at tracking the quantity and quality of longitudinal growth patterns in premature infants.³

Growth is primarily supported by the supply of protein and energy (represented by fats and glucose), in adjusted amounts and ratio, through complex pathways that reflect adaptive changes during the deposition of fat tissue, muscle tissue, and other components. Fat mass deposition, physiologically increasing through the third trimester of pregnancy, peaks at 4th-6th months after birth in breastfed infants. After this period, the rate of fat mass accumulation slows down compared to lean mass, leading to a decrease in the percentage of fat mass.⁴ The trend in formula-fed infants is reversed, with an early higher deposition of fat free mass, possibly due to a greater protein intake in front of a higher resting energy expenditure, followed by a higher deposition of fats after the 6^th month of life.⁵ The pattern of fat deposition in healthy-term infants represents the reference curve.