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Human Milk: Composition, Clinical Benefits and Future Opportunities


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(SBM) [11]. This difference could occur, for instance, if expression of the breast removed more high-fat hind milk than would be obtained by the baby if the breast was not fully emptied during feeding.

      In order to study SBM, a milk sampling system was devised by modifying a clinical nipple shield worn on the breast during breastfeeding. The modified nipple shield contained a milk sampling line so that milk could be sampled continuously during a breastfeed, and it also contained a flowmeter in the tip. Initial research using the nipple shield sampling system showed that SBM fat content was around 2.5 g/100 mL versus a figure of around 4.0 g/100 mL obtained in a vast number of prior studies on EBM composition [8, 11]. Thus, if valid, our data suggested that using EBM, it was possible to overestimate milk fat content by 60% compared to SBM obtained during normal feeding. We estimated the energy content of SBM to be 58 kcal/100 mL compared to around 71 kcal/100 mL based on over 1,500 prior publications. This would equate to a methodological error in measuring milk energy content of over 20% when studying EBM versus SBM.

      One importance of these findings is that formula manufacturers based their products, and still do, on the composition of EBM, which emerges as the wrong model.

      The higher nutrient intake of the formula-fed infants is believed to be a major factor in the faster early growth of formula- rather than breastfed infants. So, does it matter that formula-fed babies grow faster? In 2004, based on our nutritional intervention trials and animal evidence, we published our postnatal growth acceleration hypothesis, which proposes that faster early growth increases the risk for later obesity and CVD [15]. In that publication, the known increased risk of obesity and cardiovascular risk markers with formula feeding was proposed to relate to the faster growth rate. Since then, over 60 studies, including randomized trials, have supported the postnatal growth acceleration hypothesis.

      Thus, flaws in research on breast milk composition were indirectly partly responsible for the major modern epidemic of CVD and obesity – a salutary example of the importance of methodology in science. The field has now become a priority for research on both breastfeeding and formula feeding.

      The Benefits of Breastfeeding Revisited

      Arguably, the main platform for the global promotion of breastfeeding is the scientific evidence for its clinical benefits. However, with few exceptions, the comparison of breast- and formula-fed babies has not been based on randomized trials that would prove causation, but rather on observational associations.

      The challenge then is how better-quality evidence can be obtained, given the constraint that randomized trials, for instance comparing the outcome of breastfeeding versus formula feeding, are generally precluded on ethical grounds.

      The Preterm Infant as a Model

      The area I shall focus on here is the use of the preterm infant as a model. Whilst accepting that the spectrum of diseases and the sensitivity to early nutrition is somewhat different in preterm and term infants, neonatal care is an area where it has been ethically possible to conduct numerous strictly randomized trials of EHM feeding versus exposure to CM. My argument is that if a wide range of important outcomes in preterm human infants are favorably impacted by HM feeding, this would indicate that the weaker observational data on the benefits of breastfeeding in full-term infants are more likely to be causal – especially when the same outcomes (e.g., infection, allergy, cardiovascular risk, or cognitive development) can be studied in both the preterm and term populations.

      Preterm Trials Comparing Exclusive Human Milk Feeding versus Exposure to Cow’s Milk

      There are 3 categories of randomized controlled trials (RCTs) that provide evidence on the benefits of HM or adverse impact of CM.