The First-Feed Study: Milk intake, energy balance and growth in infants exclusively breast-fed to 6 months of age

Nielsen, Susan Bjerregaard (2013) The First-Feed Study: Milk intake, energy balance and growth in infants exclusively breast-fed to 6 months of age. PhD thesis, University of Glasgow.

Abstract

The World Health Organization (WHO) recommends exclusive breast-feeding until 6 months of age, where exclusive breast-feeding is defined as giving human breast milk only with no other foods or fluids. This recommendation has since been adopted by many countries. A systematic review of studies in exclusively breast-fed infants by Reilly and colleagues found a mean milk intake at 6 months of age that seemed too low to cover infant energy requirements. However, the evidence was relatively scarce, only from cross-sectional studies and based on the method of test-weighing, which has been criticised for under-estimating milk intake. Furthermore, longitudinal studies indicated no marked increase in milk intake over time, but these studies did not include measurements at 6 months of age. Reilly and Wells proposed the hypothesis that for exclusive breast-feeding to adequately cover infant energy requirements to 6 months of age, either 1) infants had to be unusually small, or 2) breast milk energy content had to be unusually high, or 3) milk intake had to be unusually high. The Reilly-Wells hypothesis was backed up by evidence of a world-wide low prevalence of exclusive breast-feeding to 6 months, and by studies consistently reporting a maternally perceived insufficient milk supply as a major reason for mothers to cease exclusive breast-feeding and introduce either formula supplementation or complementary foods.
Based on the Reilly-Wells hypothesis, the research question for the First-Feed study was: To explore how exclusive breast-feeding to 6 months of age is achievable – mainly from an energy balance point of view. The First-Feed study tested the hypothesis that successful exclusive breast-feeding to 6 months of age would include 1) infants that were small and/or growing slowly, 2) milk intakes and/or milk energy content that were higher than literature values and increasing over time, 3) infant energy requirements that were lower than reference values, and/or 4) infant feeding practices that were strained by very frequent and/or very time consuming breast-feeds. The study was designed as the first longitudinal observational study to use an isotopic method to measure milk intake and energy balance in exclusively breast-fed infants to 6 months of age, and it evaluated parts of the methodology employed in the study, in order to appreciate the results in light of the methodological strengths and limitations.
The First-Feed study found that infants were overall of normal size and growing well relative to WHO Child Growth Standards. Metabolisable milk intakes were significantly higher than the values obtained by Reilly and colleagues at both 3½ and 6 months of age, and increased significantly over time. Infant energy requirements, determined as metabolisable energy intake, was significantly higher than references for mean energy requirements at 3½ months of age, while it was appropriate at 6 months of age. Breast-feeding practices showed no change over time in feeding frequency, but a significant decrease in time spent on breast-feeds.
The First-Feed study had several limitations. Firstly, due to the inclusion criteria of exclusive breast-feeding, the participants were characterised as an affluent and well-supported sample of mother-infant pairs, who were highly motivated to breast-feed. Therefore, the generalisability of the present study to other populations should be accepted with caution. Secondly, the anthropometric measurements were prone to imprecision, as is often the case in field studies. Thirdly, the imprecision of the dose-to-infant procedure for administration of doubly-labelled water considerably reduced the precision of the doubly-labelled water method. This, in addition to the biological variation, increased the variation in some outcome variables. However, the First-Feed study is unique as it is the first to use a more objective method to measure milk intake in a longitudinal design, and on a sample of infants with a very high success rate of exclusive breast-feeding to 6 months of age.
The WHO changed the recommendation on exclusive breast-feeding from 4 – 6 months to 6 months (exactly) in 2001. Since then, many resources have been invested in breast-feeding promotion, but rates of initiation, duration and exclusivity is only slowly improving. The present study supports that exclusive breast-feeding can adequately cover infant energy requirements to 6 months of age - even without undue strain on breast-feeding practices and even in mothers where initial breast-feeding problems were very common. However, the present study found a wide variation in both infant size, milk intake and energy requirements. It therefore begs the question if a recommendation based on one age-point (6 months exactly) is appropriate given the vast biological variation in variables that are important for the adequacy of exclusive breast-feeding, or if the recommendation should be adapted to include developmental milestones (e.g. oral motor skills) indicative of readiness for complementary foods.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Human nutrition, paediatric nutrition, infant energy balance, infant health, breast-feeding, infant growth
• Subjects: R Medicine > RJ Pediatrics > RJ101 Child Health. Child health services
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Life Sciences
• Supervisor's Name: Reilly, Prof. John J.
• Date of Award: 2013
• Depositing User: Dr. Susan Bjerregaard Nielsen
• Unique ID: glathesis:2013-4378
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2013 09:39
• Last Modified: 14 Jun 2013 09:41
• URI: https://theses.gla.ac.uk/id/eprint/4378