top of page
  • Michelle Asbury, PhD

Fortifiers shape the gut bacteria of very low birth weight infants

The “gut microbiome” is the collection of bacteria and other micro-organisms (e.g., fungi, viruses, yeast) that lives in our gut. Over the first few years of life, a child’s gut microbiome rapidly develops and plays a key role in shaping their health and disease throughout life. Unfortunately, infants born very low birth weight (VLBW) develop gut microbiomes that increase their risk of disease. We are interested in studying how to change the gut microbiomes of VLBW infants to improve their health.

One promising way to change microbiomes is through early-life nutrition. Human milk is the best source of nutrition for VLBW infants, given its protection against various diseases and support of brain development. However, additional nutrients are often added to human milk, called “human milk fortifiers”, to support the growth of VLBW infants while they are in-hospital. Traditionally, these fortifiers originate from cow’s milk (called bovine milk-based fortifiers), although newer fortifiers have become available that are made from human milk itself (called human milk-based fortifiers). Since these different fortifiers are widely used in clinical care, it is important to understand how they might change the gut microbiomes of VLBW infants.

an infographic demonstrating the blinded randomized clinical trial: Nutrient enrichment of human milk with human versus bovine milk-based fortifiers.

What did we do?

Led by former PhD student Dr. Michelle Asbury, we used a randomized clinical trial to test how the gut bacteria of VLBW infants changes based on feeding either bovine or human milk-based fortifiers. Human milk containing one of the 2 fortifiers was fed to infants during their hospitalization. We then collected stools from the infants’ diapers every week to study their gut bacteria. We focused on bacteria in this study, as they make up the majority of microbiome members.

What did we find?

Compared to feeding bovine milk-based fortifiers, infants that were fed human milk-based fortifiers had bacterial profiles with limited diversity, more uniformity, and changes in specific bacteria (e.g., higher Enterobacteriaceae). Although more research is needed to understand how these specific bacteria communities affect infant health, more diverse bacterial communities with lower proportions of Enterobacteriaceae are generally associated with improved health outcomes in VLBW infants. Interestingly, we also found that infants developed more diverse bacterial communities when higher volumes of mother’s milk were fed, which may also be indicative of better infant health and development.

What’s next?

We now need to study whether these fortifier-dependent changes in the infants’ gut bacteria are associated with improved health, both in-hospital and throughout childhood. This will not only help clinical teams decide which fortifiers to feed to VLBW infants under their care, but it will hopefully improve the health of VLBW infants globally.

You can read the full paper here:

Asbury MR, Shama S, Sa JY, Bando N, Butcher J, Comelli EM, Copeland JK, Forte V, Kiss A, Sherman PM, Stintzi A, Taibi A, Tomlinson C, Unger S, Wang PW, O’Connor DL; OptiMoM Feeding Group. Human milk nutrient fortifiers alter the developing gastrointestinal microbiota of very-low-birth-weight infants. Cell Host & Microbe, 2022; 30(9): 1328-1339.E5. doi: 10.1016/j.chom.2022.07.011.


This research was supported by the Canadian Institutes of Health Research (CIHR). Dr. Asbury was additionally supported by Ontario Graduate Scholarships, the Hilda and William Courtney Clayton Paediatric Research Fund, and the Peterborough K.M. Hunter Charitable Foundation Graduate Award.

Additional Resources


Samuli Rautava. Feeding the preterm infant microbiota. Cell Host & Microbe, 2022; 30(9): 1199-1200. doi: 10.1016/j.chom.2022.08.011

News Outlets

Alejandra Manjarrez. In Search of the Best Milk Recipe for Preemies’ Gut Bacteria. The Scientist; August 22, 2022.

Bob Yirka. Comparing gut biome diversity in preemies fed human versus bovine-derived milk fortifiers. Medical Xpress; August 23, 2022:

Liji Thomas. Fortified human breastmilk alters the microbiota of low-birth-weight infants. News Medical; August 24, 2022:


bottom of page