- Human milk contains various constituents that stop infants from getting sick.
- Infants born very early or born with certain medical problems can benefit from compositional modifications to the milk they consume.
- Medically appropriate human milk modifications include increasing the concentrations of all major macronutrients, raising the concentration of particular nutrients, and reducing the odds that specific proteins in the mother’s diet get into her milk.
Unadulterated, fresh, and straight from the breast, experts agree that human milk is the best option for healthy infants. Not only does it provide the macronutrients essential to fuel and build young bodies, it actively stops infants from getting sick by dosing them with immunoglobulins and with sugars that are indigestible by humans. These sugars block viruses that otherwise would be able to attach to cells lining the gut, and they selectively feed species of bacteria that prevent nasty bacterial species from causing disease. But what if a young infant is already ill? In a recent review , Sara DiLauro and her colleagues from University of Toronto, Canada and The Hospital for Sick Children, also in Toronto, offer a summary aimed at clinicians about how human milk may be modified to cater for the particular needs of pre-term and sick infants.
Why might infants with health concerns benefit from slight alterations to normal human milk? The micro-details of the composition of human milk vary from mother to mother. But the fact that this composition changes little even when a woman is not able to eat enough is surely a strong evolutionary hint that the recipe can’t be improved.
One reason that may not always be the case is that young infants with health challenges, which would have spelled certain death for most of human evolution, are today frequently able to survive and flourish, thanks to a broad range of modern medical developments. In other words, there would have been little evolutionary pressure for the composition of the human milk to adapt to sick or premature infants’ needs. We know, for example, that the gut of a very-low-birth-weight infant is physiologically immature, meaning that what gets absorbed into the bloodstream is quite different from what gets absorbed from the gut of a normal-weight infant born at term.
Sara DiLauro and her colleagues address four human milk modification strategies. The first among them are standard strategies to raise the energy concentration of milk from about 20 kcal per ounce (0.68 kcal/ml) to whatever level is deemed appropriate. This may be appropriate for infants with unusually high metabolic demands. Such demands can arise, for example, from the development of infections like sepsis, having an atypically high resting heart rate (tachycardia), or having a lot of red blood cells per volume measure of blood—a condition called polycythemia, which can develop in response to chronic hypoxia. The authors report that an infant with congenital heart disease often does better when supplied human milk of 24–30 kcal per ounce, which can be created by adding either liquid fortifiers or powered formula to milk. The authors also warn that differences in the osmolality of the milk mixture—compared with unmodified human milk—should be carefully monitored; if the osmolality gets too high, infants may have trouble tolerating the modified milk.
In some cases, increasing the concentration of a particular human-milk component, rather than that of many macronutrients in one go, may be worthwhile. The first step in “target fortification,” as this is known, is to analyze the macronutrient content of a sample of human milk that the needy infant is consuming, so it’s clear exactly how much protein, fat, and carbohydrate he or she is getting. Then the exact amount and kind of additional nutrients can be calculated to meet individual requirements. Where it has been tried, this approach has led to more consistent growth among pre-term infants, the authors report. Nonetheless, target fortification can be expensive and logistically complicated.
Occasionally—about 2% to 3% of the time—infants show signs of an allergy to cow’s milk protein (CMPA). The percentage with this problem is much smaller among infants who are breastfed. CMPA can cause all kinds of diverse symptoms, from mucus in an infants’ stool to breathing difficulties. Among formula-fed infants, the offending source proteins come from the cow’s milk that was used to manufacture the formula; the solution to their woes, therefore, is simply to switch to a soy-based formula, assuming that breastfeeding is not an option and that the infant is not also allergic to soy, which they are about 14% of the time. Among breastfed infants, the problem is likely to be whey and casein proteins consumed by the mother and passed on in her milk. In these cases, the mother should be advised to avoid eating the sources of these proteins and see if the infants’ symptoms abate.
The last topic that the authors discuss is the modification of fats in human milk. Globules of structurally diverse fats do wonders for the healthy development of infants and appear to play a role in healthy brain development. Fats also provide up to half of the raw energy content of human milk. However, there are a few, rare medical disorders in which the provision of the usual suite of fats causes problems. Some infants, for example, have a condition called chylothorax, meaning that their thoracic duct is incompletely developed, and a substance called chyle, which is rich in triglycerides, can build up in their chests.
The method for managing infants with chylothorax are far from perfected. Although researchers have started to study ways of removing and replacing the fats in human milk, and a few specialist hospitals have offered milk with modified fat to infants with chylothorax, there are still no recommendations for the optimal milk fat level for these infants.
DiLauro and her colleagues suggest chylothorax management as an area of focus for future research. And there are many more illnesses on that list. Moreover, little is known about how populations of different species of bacteria shift over time in infants born prematurely—those who start life with physiologically immature guts. Another review, published in 2014, made a direct plea for more premature infant microbiome studies .
Information gathering through diligent lab work and careful trials will hopefully push the best medical advice forward substantially in the years ahead. But it is just that—medical advice intended for deliberation by qualified medical practitioners. Without their recommendation, human milk in its natural form is the optimal foodstuff for infants—unadulterated, fresh, and straight from the breast.
1. DiLauro S., Unger S., Stone, D., O’Connor, D. L. 2016. Human milk for ill and medically compromised infants: strategies and ongoing innovation. Journal of Parenteral and Enteral Nutrition, 40 (6): 768–782.
2. Groer, M. W., Luciano, A. A., Dishaw L. J., Ashmeade, T. L., Miller, E., Gilbert J. A. 2014. Development of the preterm infant gut microbiome: a research priority. Microbiome 2(38). http://microbiomejournal.biomedcentral.com/articles/10.1186/2049-2618-2-38
Professional science writer & editor