Is it Time to Say Goodbye to the Cow in the NICU?

Jae Kim, MD, PhD / December 2016


Each year we get closer to a reality where the only diet that is suitable for a very premature infant is one based on their mother’s milk. When that is not available, donor human milk may be a secondary substitute. In this reality, at no place is preterm infant formula a comparable replacement with early human milk feeding.

Although we are not quite ready to assume this state, I believe we have reached the tipping point where enough knowledge (and guilt) is readily apparent when decisions are made to settle with providing formula for a very preterm infant. The culprit in all this is feeding cow’s milk protein rather than the other components of formula or human milk fortifiers. Infant formula is a composite of sugar and protein from cow’s milk and fats from plants and fungi. Our human milk fortifiers are derived in a similar pattern. Cow’s milk protein then can be found in both products.

First, it might be worth considering: how did we get to the cow in the first place?

Why did we feed cow’s milk in the NICU?

It is not a new revelation that human milk is the best nutritional source for human babies. Several decades ago, preterm infants were indeed fed their mother’s milk, but without any fortification.

Given the incredible growth rates and nutrient demands of very preterm infants, these infants actually did very poorly on mother’s milk alone. Add to this the fact that mother’s milk can vary in nutrient content by more than 100% between mothers.

Compared with infants fed formula, human milk alone fed infants had poorer growth, greater metabolic bone disease and, most importantly, poorer neurodevelopmental outcomes, given their acquired malnutrition state. It took many years of practice trying to understand the fortification of human milk.

We can now safely provide a diet with human milk that gets close to the nutrient demands of our infants. I say “gets close” because I still see infants who require much more concentration than what is considered “standard” fortification (even on the higher protein containing liquid fortifiers).

At the same time, it is important to give homage to cow’s milk, as we must recognize the importance that cow’s milk derivatives, such as infant formula, have had in supporting rapidly growing preterm babies. Without the period of time when we had these formulas, I think we would have hobbled through with significant poor growth and development before we better understood how to fortify human milk.

Over the years, nutrition companies have made some terrific advances with preterm formulas starting with the balancing of the casein:whey protein ratios, or eliminating casein altogether to improve gastric emptying and feeding tolerance. They adjusted the fatty acid profiles and content of long chain fatty acids in formula, and added numerous other components such as nucleotides, luteins, carotenoids to match some of the performance seen with human milk ingredients.

While our complacency with providing intact cow’s milk protein is long overdue, the exact mechanisms of the protein’s badness is much less clear. How much are all these effects a problem with cow’s milk protein versus the positive benefits of the bioactive components and healthy microbiome promoting human milk? There are good arguments for both, and perhaps it would be fair to conclude that both reasons are at play.

There are no questions that many components in human milk provide dramatic immunologic and microbiome protection such as with immunoglobulins, lactoferrin, lysozymes, prebiotics and probiotics. However, relatively modest amounts of cow’s milk protein in the face of all these protective components still correlate with the development of necrotizing enterocolitis (NEC).1

Why we say hello to human milk feeding in the NICU

The recognition that mother’s milk contained many hundreds of compounds that are not replicated in infant formula, and that these confer tremendous short-term and long-term health advantages for preterm infants, was slow to emerge. Traditional medical teaching, already short-changed on nutrition education, provided minimal to no information on the biologic benefits of human milk to arm future physicians and healthcare providers.

The surge in use of donor human milk over the past decade, with more than a doubling of available donor milk banks in the country, suggests that the recognition of the prowess of human milk over infant formula is now widespread as the primary end user of donor milk is the NICU (

Recently the much awaited Canadian donor human milk study (DoMINO) completed and demonstrated that despite some concern that donor milk suffers in being of lower quality than mother’s own milk, it continues to support the most compelling premise that human milk (whether mother’s own or donor milk) reduces the incidence and severity of NEC, the most feared gastrointestinal affliction of preterm infants.2

Together as a neonatal community, we have embarked on a unique post-market experiment over the past five years where many of our NICUs have eliminated the presence of intact cow’s milk protein with the use of several hydrolyzed cow’s milk protein-containing liquid human milk fortifiers.

While we don’t have any data to suggest the effect of this dramatic change in diet on conditions such as NEC, I would postulate that having less bovine components may eliminate some of the badness we have long associated with intact cow’s milk protein, and alleviate some morbidity from our infants. Time and some careful quality improvement data may enable us to reveal these potential broader effects.

The uniqueness of mother’s milk should no longer go unnoticed. The impressive immunologic protection that it provides for all our babies should compel us to find better ways to support our mothers in the arduous task of pumping their milk, as well as gain a broader donor base to draw upon for the provision of equally precious donor human milk.

In San Diego we have recently taken up the charge to find more human milk donors in our community through the development of a Southern California donor human milk bank. Our ultimate mission, like so many before us, is to tip the scales one last time to ensure that ALL very premature babies have access to and drink only from the human well. So join me and others in giving intact cow’s milk protein a fond farewell for our very preterm babies. Bon voyage!

Looking for more from Dr. Kim?

Read Getting the Skinny on Malnutrition in the NICU.


  1. Sullivan S, Schanler RJ, Kim JH, Patel AL, Trawöger R, Kiechl-Kohlendorfer U, Chan GM, Blanco CL, Abrams S, Cotten CM, Laroia N, Ehrenkranz RA, Dudell G, Cristofalo EA, Meier P, Lee ML, Rechtman DJ, Lucas A. An exclusively human milk-based diet is associated with a lower rate of necrotizing enterocolitis than a diet of human milk and bovine milk-based products. J Pediatr. 2010 Apr;156(4):562-7.e1. doi: 10.1016/j.jpeds.2009.10.040.
  2. O’Connor DL, Gibbins S, Kiss A, Bando N, Brennan-Donnan J, Ng E, Campbell DM, Vaz S, Fusch C, Asztalos E, Church P, Kelly E, Ly L, Daneman A, Unger S; GTA DoMINO Feeding Group.. Effect of Supplemental Donor Human Milk Compared With Preterm Formula on Neurodevelopment of Very Low-Birth-Weight Infants at 18 Months: A Randomized Clinical Trial. JAMA. 2016 Nov 8;316(18):1897-1905. doi: 10.1001/jama.2016.16144. PubMed PMID: 27825008.


About the Author

Jae Kim is an academic neonatologist and pediatric gastroenterologist and nutritionist at UC San Diego Medical Center and Rady Children’s Hospital of San Diego. He has been practicing medicine for over 23 years both in Canada and the USA. He has published numerous journal articles, book chapters, and speaks nationally on a variety of neonatal topics. He is the Director for the Neonatal-Perinatal Medicine Fellowship Program at UC San Diego and the Nutrition Director of an innovative multidisciplinary program to advance premature infant nutrition called SPIN (Supporting Premature Infant Nutrition, He is the co-author of the book, Best Medicine: Human Milk in the NICU. Dr. Kim is a clinical consultant with Medela, Inc.