The Nutritional Science of Human Milk

 

The research behind human milk is expanding exponentially. At the most recent Pediatric Academic Society meeting, there were any number of presentations and posters around this topic. As more and more becomes known about the nutrition provided through breast milk and the nutritional needs of the preterm infant, efforts are made to bridge this gap. In a previous blog, I talked about the loss of fat in the tubing and syringe of a gavage feeding. Two research studies presented as posters looked at various ways to decrease this fat loss (Lipid and Energy Losses are Greater with Prolonged Feeding Times, Smith RW, Radmacher PG, Adamkin DH; Optimizing fat delivery methods in continuous enteral feeding of expressed breast milk to neonates, Abdelrahman KM, Hair AB, Hawthorne KM, Abrams SA). Shorter feeding time, upright positioning of the pump and agitation of the milk were all studied. In spite of all these measures, significant fat loss was observed. This happened over as short a time as 1 hour! The recommendation of these researchers was to provide breast milk feedings as a bolus or gravity feed whenever possible.

Another quite interesting study called the Global Exploration of Human Milk, funded by Mead Johnson, is a study in which 365 mother/infant breast feeding cohorts were studied in China, the U.S. and Mexico. There were 120 in China, 120 in the United States and 125 in Mexico.   This was an exploratory study to examine the longitudinal effect of the environment, diet and culture on breast milk and infant growth. Mothers were enrolled in the study within 4 weeks of delivery and had to agree to continue breast feeding for at least 3 months.

In an already published report of this study, Woo, Guerrero, Ruiz-Palacios et al (2013) reported that growth rates were significantly different with the Chinese infants being heavier and longer than babies in the U.S. or Mexico. It was found that exclusive breast feeding was moderately inversely associated with weight gain but not length or body mass index. No feeding practices completely explained this difference. At the PAS meeting, a part of this study was reported in which the breast milk was collected from a subset of the mothers in each cohort at 4 wks and 26 wks after delivery. The protein content in the milk was comparable across geographic regions at 4 weeks but was significantly different by 26 weeks after birth. The conclusion from this portion of the study was that protein content in the milk up and down regulates over the course of lactation which is already known but that these changes are different in different geographic regions (Comparative Analysis of the Human Milk Whey Proteome Across Populations and Lactation Stages: GEHM Study Insights. Zhang Q, Lohe K, Cundiff J, et al). One comment that was made in relation to protein content of human milk in general was that we are studying the protein content but perhaps it is important that we know which amino acids are or need to be present in the diet. This is something that has been discovered in parenteral nutrition and perhaps it is important as well in the enteral diet.

Several researchers are studying neonatal growth and particularly gain of lean body mass which reflects appropriate growth and not just an increase in weight. One study found that infants who had larger fat mass compared to lean body mass had considerably weaker bones as well (Fat Mass in Extremely Preterm Infants: Relationship With Neonatal Weight Gain, Tremblay G. et al 2903.442). So, how do we provide adequate nutrition leading to appropriate growth and development rather than additional body fat? Most likely, this is through providing adequate protein in the diet rather than just increasing calories as well as fortifying according to the individual needs of the infant based on nutrition of the mother’s own milk or donor milk, whichever is being fed. This requires efficient analysis of the milk to determine the nutritional content, both calories and protein. Some poster presentations and at least one oral presentation discussed the use of this analysis (Individualized Nutrition Precision of Macronutrient Fortification of Human Milk, Smilowitz JT et al 2900-414; Validation of NIR Milk Analyzer for Pasteurized and Native Milk, Sheen WT et al 2901-420; Comparison of Macronutrient Composition of Human Breast Milk Using Two Methods of Analysis, Parat S et al 1172.5). Different machines are used to do the analysis but one in particular takes up to 30 ml or one ounce of milk to complete the analysis! In addition, since the nutritional content of the milk changes over time, it is important to analyze it periodically and adjust the infant’s diet. In the study mentioned above, this was done on a weekly basis. Given that the requirement for milk is so high in order to do the analysis, along with other factors, it’s not quite ready for prime time in the clinical area.

So while we know more and more about both the nutritional content of breast milk and premature infant’s nutritional needs, making this match precisely remains difficult. The challenge is to ensure that these infants do not experience extrauterine growth failure which remains all too common. The nutrition required for proper growth is also necessary for neurodevelopmental growth with growth failure increasing the risk of cerebral palsy and poor neurodevelopmental outcome (Ehrenkranz, Dusick, Vohr et al, 2006).

References:

Ehrenkranz RA, Dusick AM, Vohr BR, Wright LL, Wrage LA, Poole WK et al. Growth in the neonatal intensive care unit influences neurodevelopmental and growth outcomes of extremely low brith weight infants. Pediatrics. 2006;117:1253-61.

Woo JG, Guerrero ML, Ruiz-Palacios GM, Peng YM, Herbers PM, Yao W, Ortega H, Davidson BS, McMahon RJ, Morrow AL. Specific infant feeding practices do not consistently explain variation in anthropometry at age 1 year in urban United States, Mexico, and China cohorts. J Nutr. 2013;143(2):166-74. doi: 10.3945/jn.112.163857.

 

About the Author

Sandy Sundquist Beauman has over 30 years of experience in neonatal nursing. In addition to her clinical work, she is very active in the National Association of Neonatal Nurses, has authored or edited several journal articles and book chapters, and speaks nationally on a variety of neonatal topics. She currently works in a research capacity to improve healthcare for neonates. Sandy is also a clinical consultant with Medela. You can find more information about Sandy and her work and interests at https://www.linkedin.com/in/sandy-beauman-0a140710/.