The statement ‘It is unclear why human breast milk stands out among that of other mammals. It has five times as many types of H.M.O.s as cow’s milk, and several hundred times the quantity. Even chimp milk is impoverished compared with ours‘ is in a recent New Yorker article. Its premise is inaccurate. Published data from 2011 directly contradicts it, specifically, by showing chimpanzee and human milk oligosaccharides (HMOs) are comparably diverse and abundant (see figure below from), though HMOs have higher degree of polymerization. Ironically, this paper is authored by University of California, Davis, researchers, including one of the persons interviewed in this New Yorker piece, Bruce German.
I was also taken aback to read the following grossly inaccurate generalization in the same New Yorker piece,
‘The number of scientific publications about milk is tiny, compared with the number devoted to other bodily fluids—blood, saliva, even urine. The dairy industry has spent a fortune on extracting more and more milk from cows, but very little on understanding just what this white liquid is or how it works. Medical-funding agencies have generally dismissed it as irrelevant, German said, because “it doesn’t have anything to do with the diseases of middle-aged white men.”’
Sure, there are likely many more scientific publications dealing with blood, saliva and urine compared to milk. After all, they’re easily accessible sources to sample circulation to perform diagnoses, as well to simply study physiology. OTOH, milk is typically only made and secreted by lactating adult female breasts. Can’t use milk to diagnose conditions in children, men and non-lactating women, who can usually provide blood, saliva or urine samples any time during their life. In other words, disingenuous to argue diseases of middle-aged white men preclude research funding for studying milk. By the way, all that greater effort into studying blood has still not yielded an adequate fully synthetic replacement to human plasma, i.e., expense and effort alone don’t dictate outcome. As well, having spent several years on a project that used sheep milk proteins as* may not make me a milk expert but I know enough to know those statements in the article are gross exaggerations to say the least, for the following reasons.
- Embarking on that project, I soon discovered and consulted with a nearby world expert on one of those milk proteins. The recently retired Pradman K. Qasba from the Frederick, Maryland, campus of the , spent the bulk of his career studying just this one milk protein, .
- Milk’s of considerable interest to evolutionary biochemists interested in how milk components may have evolved as a result of events. For example, sequence comparisons suggest alpha-lactalbumin to be the product of gene duplication, an event that may have occurred around the time Mammals spilt from Birds.
- Alpha-lactalbumin’s also a protein of tremendous interest to biochemists because it belongs to a select class of very intriguing proteins capable of existing in the state.
- And how could one talk of alpha-lactalbumin and its capacity to assume a molten globule state without mentioning , the Swedish microbiologist, who since at least 2000 has shown repeatedly in the peer-reviewed scientific literature that HAMLET (Human Alpha-Lactalbumin Made Lethal To Tumors) can apparently kill tumors directly?
- This is barely scratching the surface of research on just this one milk component. And as recently as March 2012, Catharina Svanborg was an invited speaker at University of California, Davis’ Foods for Health Institute, where the afore-quoted Bruce German works ( ).
- Also important to note that the study of alpha lactalbumin is inextricably tied to that of milk sugars. Arguably among the most abundant of milk sugars, albeit a disaccharide, not oligosaccharide, synthesis requires alpha lactalbumin.
A 2012 review on HMOs by Lars Bode helpfully includes a >100 year retrospective (see figure below from).
Thus, it doesn’t reflect well on the New Yorker to not have more carefully vetted this science-related article that contains such inaccurate generalizations. Lazy science journalism doesn’t just do disservice to science, no, it’s also dangerous in its potential to further fray the public’s increasingly fragile trust in the scientific enterprise. Anyway, this brief deconstruction suggests to not take some of this article’s assertions at face value.
Differences in milk composition between species are several and well-documented. While primate milk tends to contain greater variety and quantity of oligosaccharides compared to those of ruminants like cows, milk from the latter is abundant in, which is completely absent in human milk. Donkey milk contains a greater variety and amount of and compared to human milk ( ), a difference that’s stoking some interest in developing it as a .
What do such differences mean? At a minimum, they demonstrate exquisite adaptations of milk composition to different selection pressures imposed by specific ecological niches and specific life history-driven demands of babies of different mammalian species. What those different selection pressures specifically are remain speculations at present. Upon reflection, aren’t differences in composition between milks from different species only to be expected? Different mammalian species may need to have different milk components to
- Prepare their newborn’s gut to be colonized by different microbes, i.e., different milks with different potential accurately reflect the different ecological niche each species occupies. Such differing components would help different microbes to colonize a newborn’s gut as well as help protect against pathogens that each newborn mammalian species would need protection from, obviously something where different mammals likely differ. One way milk sugars could protect against pathogen invasion is by binding to carbohydrate binding proteins, especially on viruses, i.e., functioning as decoy molecules to clear them from the body. For example, human milk glycosaminoglycans can bind to ‘s ( ).
- Satisfy different energetic/caloric requirements of different newborn species. For example, calves and foals start to graze and forage by themselves within a few days to few weeks of birth, obviously a drastically different situation from that of human babies. A calf or foal’s nutritional demands on cow or horse milk would thus likely be far less onerous compared to those of a human baby’s on human milk.
- Account for different strategies adopted by different mammalian species, account in terms of one species needing to provide post-birth some essential nutrient that another species may already provide in utero. A salient example is greater need for immediate post-birth in bovines and equines, which have less invasive epitheliochorial placenta compared to primates, which have more invasive haemochorial placenta. One result of this placentation difference is relative lack of in utero transfer of maternal antibodies in cows, sheep and horses, which is why newborn calves, lambs and foals need to immediately post-birth drink colostrum, their main source of maternal antibodies.
1. Tao, Nannan, et al. “Evolutionary glycomics: characterization of milk oligosaccharides in primates.” Journal of proteome research 10.4 (2011): 1548-1557.
2. Goto, Kohta, et al. “Chemical characterization of oligosaccharides in the milk of six species of New and Old world monkeys.” Glycoconjugate journal 27.7-9 (2010): 703-715.
3. Bode, Lars. “Human milk oligosaccharides: every baby needs a sugar mama.” Glycobiology 22.9 (2012): 1147-1162.
4. Chiofalo, Biagina, et al. “Comparison of major lipid components in human and donkey milk: new perspectives for a hypoallergenic diet in humans.” Immunopharmacology and immunotoxicology 33.4 (2011): 633-644.
5. NEWBURG, DAVIDS, et al. “Human milk glycosaminoglycans inhibit HIV glycoprotein gp 120 binding to its host cell CD4.” J Nutr 125 (1995): 419.