Nutrient-enriched formula linked to increased head circumference and lower fat mass in a subset of preterm infants

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Key study points:

1. Preterm infants whose birth weight was appropriate for gestational age (AGA) had higher head circumferences and lower fat mass percentages when fed nutrient-enriched formula, as compared to standard formula.

2. The type of formula fed to small for gestational age (SGA) infants had no effect on growth parameters over the first twelve months of life.

Primer: When fed formula quantities consistent with recommendations for term infants, preterm babies often exhibit continued growth restriction after hospital discharge. Since stunted postnatal growth is linked to worse cognitive outcomes later in life, effective feeding of infants born preterm is important both before and after newborns leave the hospital. However, some studies have found that that promoting too rapid a rate of “catch-up” growth in early life may lead to higher fat mass, insulin resistance, and metabolic syndrome in adulthood. The effect of using formula that is either energy- or nutrient-enriched on growth and fat mass outcomes in pre-term infants is not fully known. Post-discharge, nutrient-enhanced formulas have been linked in some studies to improved growth, bone formation, and cranial growth. The current study aimed to further elucidate the potential benefits of nutrient-enhanced formulas, when compared to standard formula, on adiposity composition in preterm infants in the year after hospital discharge. This was the first known study to consider the influence of formula composition on growth and fat mass composition in preterm infants categorized as AGA or SGA.

Background reading:

1. Growth of preterm infants fed nutrient-enriched or term formula after hospital discharge [Pediatrics]

2. Optimal growth and lower fat mass in preterm infants fed protein-enriched postdischarge formula [Journal of Pediatric Gastroenterology and Nutrition]

This [prospective, randomized controlled] study included 207 infants who were born at < 32 weeks gestational age and/or weighed < 1500 grams, and received >80% of their nutrition from sources other than breast milk. Babies were grouped according to size for gestational age, as either AGA or SGA.  The infants were randomized to receive either 6 months of exclusive standard formula or  nutrient-enriched formula. Daily formula consumption was recorded. Weight, length, head circumference, and body composition were measured once the babies reached term and then 1, 3, and 6 months at term-corrected age, and all parameters except body composition were additionally measured at 12 months.

Despite drinking less milk than those fed standard formula at 1 and 3 months, SGA and AGA infants fed nutrient-enriched formula had higher protein intakes. Average head circumference was significantly higher in AGA infants receiving nutrient-enriched formulas at 6 and 12 months, when compared to those receiving standard formula, but did not differ at any time between SGA babies receiving the different formulas. In addition, after 6 months, AGA infants given nutrient-enriched formula showed similar weights, but had lower fat mass percentages when compared to AGA babies given standard formula. SGA infants did not show any significant differences in fat mass as a result of receiving the nutrient-enriched formula.

In sum: The findings of the current study are consistent with and strengthen recent literature on catch-up growth patterns in preterm infants. As preterm infants are thought to be at increased risk for growth retardation and slowed brain development throughout life, it is particularly salient that AGA infants receiving nutrient-enriched formula had significantly higher head circumferences, an indicator of cognitive development, as well as increased fat-free mass gain, than their standard formula-fed counterparts. Whether fed nutrient-enriched or standard formula, the two groups of SGA infants did not differ in any of the measured outcomes. This study indicates the advantages of feeding AGA preterm infants nutrient-enriched formula; however, additional, long-term studies assessing cognitive function, body composition, and risk of metabolic syndrome would be necessary to affirm the significance of these potential benefits throughout a child’s life.

Click to read the study in [Pediatrics]

By [LHC] and [DB]

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