Protein Intake and Growth in Preterm Infants: A Systematic Review

Abstract

Objective. This review aimed to investigate the relationship between varying levels of enteral protein intake and growth in preterm infants, regardless of feeding method. Data Sources. Electronic databases were searched for relevant studies, as were review articles, reference lists, and text books. Study Selection. Trials were included if they were randomized or quasirandomized, participants were <37 weeks gestation at birth, and protein intakes were intentionally or statistically different between study groups. Trials reporting weight, length, and head circumference gains in infants fed formula, human milk, or fortified human milk were included. Data Extraction. Studies were categorized by feeding-type and relevant data were extracted into summary tables by one reviewer and cross-checked by a second. Data Synthesis. A meta-analysis could not be conducted due to extensive variability among studies; thus, results were synthesized graphically and narratively. Twenty-four trials met the inclusion criteria and were included in a narrative synthesis and 19 in a graphical synthesis of study results. Conclusions. There was extensive variability in study design, participant characteristics, and study quality. Nonetheless, results are fairly consistent that higher protein intake results in increased growth with graphical representation indicating a potentially linear relationship. Additionally, intakes as high as 4.5 g/kg/day were shown to be safe in infants weighing >1000 g.

Keywords: dietary proteins; growth; human milk; infant; premature.

Figure 1.

Flow diagram of search methods.

Figure 2.

Relationship between protein intake and weight gain. Five studies did not report weight gain in g/kg/day and thus were excluded.^,,,, Formula studies are indicated with black, unfortified versus fortified HM studies with white, and studies comparing different HMFs with grey markers. The solid black line represents the clinically used weight gain target of 15 g/kg/day. The dashed line represents the recently updated weight gain target that accommodates catch-up growth, 20 g/kg/day.