Human Milk: Composition, Clinical Benefits and Future Opportunities. Группа авторов

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СКАЧАТЬ discordance and how this should be managed to complement the considerable value of breastfeeding identified later in this article. Thus, modern mothers eat less green leafy plants than our ancestors and presumably have less vitamin K in their breast milk [3]. This may explain the past occurrence of late vitamin K deficiency bleeding in modern breastfed infants – a condition that had a high incidence of intracranial bleeding. Thus, all babies now receive prophylactic vitamin K after birth. A further example is that a consequence of recent migration of human populations into less light-exposed areas of the globe is increased propensity to vitamin D deficiency, which may require vitamin D prophylaxis. An intriguing hypothesis to explain the occurrence of early iron deficiency anemia comes from the observation that piglets put in a concrete pen develop iron deficiency since pig’s milk is relatively low in iron and a concrete pen prevents iron intake from soil [4]. Hallberg [5] speculated that early human infants might have eaten soil to supplement the iron received from human breast milk, but with environmental change and modern public health, modern infants no longer consume iron from soil.

One consequence of the major recent change in the diet of humans is that the n-6/n-3 fatty acid ratio in the diet of hunters-gatherers is believed to be around 1: 1 whereas with a modern Western diet this ratio is around 15: 1, reflecting a relatively low n-3 fatty acid status in modern mothers [6]. The impact of supplementing the diet of a lactating mother with n-3 fatty acids is not established but does at least raise the hypothesis for future testing that nutritional status of the offspring might be further optimized by dietary care of breastfeeding mothers.

      In summary, current evidence (see later) shows that breastfeeding is superior to its substitutes on numerous health grounds. Nevertheless, given the evolutionary aspects considered, it is in the interests of population health to identify areas in which nutritional care of breastfeeding mothers or their babies could further improve outcome – a principle already in practice in relation to the use of prophylactic vitamin K and vitamin D in infancy.

      Breast Milk Composition as the Gold Standard for Infant Nutritional Needs

      HM composition has generally been regarded as a gold standard for deriving infant nutritional requirements – for instance in situations where artificial feeding is required. This has certainly been a most helpful concept.

      However, for breast milk to be a valid gold standard, it is critical that accurate data are obtained using appropriate methodology. This latter aspect is the one that is discussed in this section since it will be argued that despite intensive work on the composition of breast milk, misleading data have been derived in the past that have misdirected nutrition practice in ways that have had adverse impact on babies and their long-term health.

In 1953, Hoobler et al. [7] were able to summarize no less than 1,500 scientific publications on the composition of HM. In 1977, the UK Department of Health added further to this list: an official publication on the nutrient content of breast milk obtained by complete expression of one breast in mothers from 4 UK cities [8]. These data were proposed to provide a basis for infant nutritional needs and a model for the design of infant formulas. It was at this stage that this and past studies on breast milk composition were challenged as methodologically flawed [9].

One major difficulty in the study of breast milk content is obtaining representative samples of breast milk for analysis. Breast milk fat, and hence energy content, varies greatly during a feed, between breasts, and throughout lactation. Our own data show that during the course of a breastfeed, breast milk fat content doubles, and milk flow, statistically at least, decreases in a curvilinear manner [10]. We suggested that obtaining representative values for milk fat might be best derived by studying milk composition and milk flow during the feeding process, yet this had never been done. In the absence of such knowledge, we hypothesized that milk obtained for analysis in the traditional manner by unphysiological manual or mechanical expression of the breast – so-called expressed breast milk (EBM) – might differ greatly in its fat and energy content compared to the milk obtained by the baby during physiological breastfeeding – termed by Lucas “suckled breast milk” (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.

When these data on SBM were published, they were too radically different to those published previously using EBM to be widely accepted. So, to confirm our findings on the energy content of breast milk, we used the doubly labeled water method in a novel way. In this method, 2 naturally occurring stable isotopes: deuterium (heavy hydrogen, ²H) and heavy oxygen (¹⁸O) are given orally producing enrichment of these isotopes in body fluids. Decline in these isotope enrichments back towards baseline is measured in urine or saliva over several days. The slope of the decline in ²H can be used to measure water output (since hydrogen is lost as water), which in steady state reflects water intake, and, from this, milk volume intake can be derived. The decline in ¹⁸O is faster since oxygen can be lost in both water and carbon dioxide. Hence, the difference in the decline in ²H and ¹⁸O is the CO₂ production rate, from which energy expenditure can be derived – and hence metabolizable energy intake. Thus, over several representative days, milk volume intake and energy intake can be estimated, and, by dividing the latter by the former, the energy content of breast milk is derived without any recourse to breast milk sampling. This approach produced values for energy content of breast milk according to postnatal age of 57–61 kcal/100 mL, thus confirming our previous values using the nipple shield system [12]. Later work has confirmed our finding that breast milk energy content had been greatly overestimated in past EBM studies.

      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.

In addition to errors in prior estimation of breast milk fat and energy, breast milk protein content was also overestimated by using analytic methodology developed by the dairy industry. In cow’s milk (CM), there is little nitrogen that is not part of protein so that it is possible to estimate protein content by multiplying nitrogen content by a constant (6.38) [13]. This was used inappropriately for human breast milk in which there is a high content of nonprotein nitrogen (e.g., urea), which should not be counted as protein. Thus, more recent work shows that the СКАЧАТЬ