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The Milk Machine: Learning More about How Breastmilk Protects the Gut

Maryanne Perrin, MBA, and ILCA volunteer

Research over the last several decades has highlighted WHAT makes human milk so amazing — it’s associated with reduced risk of infections, asthma, obesity, diabetes, leukemia, and necrotizing enterocolitis (NEC), just to name a few. Determining HOW human milk delivers these benefits (referred to as “the mechanisms”) is less fully understood, though researchers around the world are working on these questions. A study published last month in the journal Pediatric Research gave some interesting insights on a potential human milk mechanism that is involved in protecting against NEC.

Photo by derPlau via Flickr Creative Commons

Photo by derPlau via Flickr Creative Commons

First, a little background information: Most of the fat in our diet is found in the form of triglycerides, a “suitcase” that carries three (thus the “tri”) fatty acids bound to a glycerol backbone. To absorb these fats, our bodies first break off the fatty acids, producing free fatty acids (FFAs), which are packaged into micelles and absorbed via the intestinal epithelial cells, and then repackaged into triglycerides for transport to other tissues.

Researchers at the University of California, San Diego wondered whether there was a difference in the toxicity of digested human milk (HM) compared to infant formula (IF), so they used an in-vitro model to study what happened to various cells when exposed to digested HM and IF. This involved mixing HM and IF in test tubes with various enzymes to simulate the digestive process, and then exposing three different cell types to the digested content: human neutrophil cells (a white blood cell that is involved in the early response to infections); cow heart endothelial cells, and rat intestinal epithelial cells.

What did they find?

Digested infant formula had significantly higher levels of FFAs than digested human milk (more triglycerides were cleaved) and it also had significantly higher death rates of neutrophils during a two hour exposure (ranging from 47 – 99% depending on the formula brand compared to a 6% death rate during exposure to digested human milk). Results were similar for the death of cow heart cells and rat intestinal cells. The likely mechanism for the cell death is the elevated level of FFAs which act as detergents and rupture cell membranes. When FFA levels were reduced by inhibiting the enzyme that cleaves triglycerides, cell death was also reduced.

Infant formula is designed to have a similar fat content to human milk, so what could cause the elevated FFAs levels that contribute to necrosis? The authors speculated on several things including the way triglycerides are delivered in human milk (they are in larger globules than in infant formula, potentially making them less digestible by lipase enzymes), the possibility that human milk deactivates enzymes that digest fat (or infant formula activates them), and the different structure of the triglycerides (human milk puts the long chain fatty acids in the #2 position on a triglyceride, making them less digestible, while in infant formula, the long chain fatty acids are primarily located at position #1 or #3 on the glycerol backbone, which is preferentially cleaved by digestion enzymes).

The mechanism described in this study is not pathogen driven, but instead driven by a cytotoxic environment that leads to premature cell death. Other potential NEC mechanisms were reported in the last year that involved bacteria; one study done in a rat model showed that the oligosaccharides in human milk bind pathogens that cause NEC, while another study showed that bacteria that grew on human milk formed a potentially protective biofilm. All of these studies were done in a test tube or in animal models, which means more research is needed to determine whether these mechanisms also operate in humans.

Collectively these studies suggest that human milk potentially has a variety of “tools in its toolbox” for protecting the immature and developing infant. Does this surprise you?!

MaryannePerrin3-2Maryanne Perrin loves all things related to food: growing it, cooking it, eating it, and now studying about it at the molecular and cellular level.  She has a BS in Industrial Engineering from Purdue University and an MBA from the University of North Carolina, Chapel Hill, and enjoyed a variety of career paths (information technology, management consulting, stay-at-home-mom, entrepreneur) before returning to school to obtain a PhD in Nutrition Science. She was quickly captivated by the amazing story of human milk and is focusing her research on understanding the nutritive and immunoprotective value of donor milk beyond one year postpartum.  When she’s not studying or helping ILCA with social media, she likes playing in the woods with her husband, three kids, and the family dog.  


Can A Cow Jump Over the Moon (or Produce Human Milk)?

By Maryanne Perrin, MBA

Photo by law_keven via Flickr Creative Commons

“Hey diddle diddle,
The cat and the fiddle,
The cow jumped over the moon.”

How many of us have lulled little ones to sleep with the lines from this old English nursery rhyme? Today’s news headlines claim cows are performing another impressive trick –producing human milk – thanks to the wonders of genetic engineering. And while cow tricks are amusing in nursery rhymes, in the field of infant nutrition they deserve a lot more scrutiny. So let’s take a closer look at the claims of human-milk-producing cows.

What’s Been Engineered Into Cows’ Milk

In recent years, scientists in China have genetically modified cows to produce human lysozymes, an antimicrobial protein (1) that disrupts the cell wall of gram-positive bacteria. They’ve also created a cow that produces human lactoferrin, another important antimicrobial protein (1) that destabilizes the cell wall of both gram-positive and gram-negative bacteria. A 2011 study out of The Netherlands found that the lysozyme content of human milk was 3,000 times greater than that of bovine milk, and that the lactoferrin content was 75 times greater (2). Clearly the greater concentrations of these antibacterial proteins in human milk are important for infants, given the immature nature of their gastrointestinal tract. But does adding a genetically engineered human protein to cow milk provide the same immunological benefits to humans (many more studies will be needed to establish safety and efficacy) and are there other important human milk compounds missing from engineered cows’ milk?

What’s Still Missing?

We’ve learned a lot over the past few decades about the make-up of human milk (and there’s still more to be discovered and understood!). Two of the most obvious areas where human milk and bovine milk differ in their nutrient make-up are in proteins and carbohydrates.

Proteins: Both the quantity and nature of proteins differ between human and bovine milk. For example, human milk has substantially less total-protein and casein-protein than cows’ milk, while it has significantly higher concentration of several proteins associated with the development of the mucosal immune system. The Netherland study showed that of the 268 proteins identified in human milk, 121 of these proteins (45%) were not found in cow milk (2).  Notable differences include the high concentration of immunoglobulin A, a human milk protein customized to bind pathogens found in the mother’s (and thus the baby’s) environment, and CD14, a protein involved in detecting gram-negative bacteria and activating the innate immune system.

Carbohydrates: Human milk has a higher concentration and more diverse portfolio of oligosaccharides, (a short chain of sugar molecules) than cow milk (3). Human Milk Oligosaccharides (HMOs) pass through an infant’s gut undigested, and serve as a prebiotic for the development of a healthy gut microflora. They also appear to act as a very shape specific “lock and key” to bind pathogens. While much research remains to be done in this field, recent studies have shown HMOs to be protective against NEC in an animal model, and to be associated with a reduced transmission of HIV.

Today’s scientific advances will allow us to continue to identify health-promoting compounds in human milk and then manufacture them using various biotechnologies. But “human milk” cannot be created by bolstering cow milk with one or two important proteins, as evidenced by the hundreds of unique proteins and hundreds of unique and changing oligosaccharides in human milk (not to mention living cells and bacteria) that work collectively to support an infant’s immature immune system. Re-engineering all of that into a single cow is a mighty big challenge – probably even bigger than jumping over the moon!

Written by Maryanne Perrin, MBA, Graduate student in Nutrition Science, and ILCA volunteer


1. Hanson, L.A. (2005). Human milk: Its components and their immunobiologic functions. In J. Mestecky, M. Lamm et al (Eds.), Mucosal Immunology 3rd Edition ( 1795-1827). Oxford: Elsevier Academic Press.

2. Hettinga K, van Valenberg H, de Vries S, Boeren S, van Hooijdonk T, et al. (2011) The
Host Defense Proteome of Human and Bovine Milk. PLoS ONE6(4): e19433. Doi:10.1371/

3. Mehra R, Kelly P. Milk oligosaccharides: Structural and technological aspects. International Dairy Journal. 2006; 16(11): 1334-1340.


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