Preterm infants are born with underdeveloped gastrointestinal systems, making them especially vulnerable during the first weeks of life. Their gut lining is fragile, immune responses are incomplete, and the microbial environment is not yet established. 

This stage is critical. The nutrition they receive, whether breast milk, donor milk, or formula, can have lasting effects on gut development, immune protection, and disease risk. 

This post explores human breast milk, donor milk, and the effect of probiotics on premature babies’ gut health. It also discusses why parents should avoid cow-based milk formulas.

How Breast Milk Supports Gut Health

Breast milk plays a vital role in building and protecting a newborn’s digestive system, especially for premature infants. Unlike a formula, it is rich in live, bioactive compounds that directly support gut development and immune function.

One of the most important components in breast milk is human milk oligosaccharides (HMOs). Nestlé Nutrition Institute highlights that preterms often lack certain HMOs, increasing their risk for health problems. HMOs are the third most abundant solid component in human milk after lactose and fat. It helps improve these microbial patterns.

Another important compound is the milk fat globule membrane (MFGM). It surrounds fat droplets in breast milk and supports brain development while also strengthening the gut lining. 

A study in RSC Publishing highlights that MFGM-PL supplementation enhanced the expression of several key markers associated with gut health. It increased Ki-67, a protein involved in cell proliferation, supporting intestinal growth and renewal. Lysozyme, which helps eliminate harmful bacteria, was also upregulated. Additionally, the expression of Mucin 2, responsible for forming a protective mucus layer in the gut, was improved.

Breast milk also supports the development of tight junctions (structures that hold the cells of the intestinal lining closely together). These junctions prevent the leakage of harmful substances from the gut into the bloodstream. This barrier function is critical in reducing the risk of systemic infections in vulnerable preterms.

Risks Linked to Cow’s Milk–Based Formula

Cow’s milk–based formula lacks many bioactive components that support gut health in newborns. It does not contain human milk oligosaccharides (HMOs), immunoglobulin A (IgA), lactoferrin, or other protective elements found in human milk. These missing elements play a key role in shaping a healthy gut environment and immune response.

The Birth Injury Center highlights that cow’s milk-based infant formula is linked to a higher risk of NEC. Necrotizing Enterocolitis (NEC) is a serious condition in newborns involving severe inflammation in the intestines.

Breast milk (from mothers or donors) appears to protect against NEC. It contains compounds that help in controlling harmful bacteria and reducing inflammation. Cow’s milk lacks these protective elements, allowing dangerous bacteria to grow, increasing NEC risk. 

However, not all formulas are linked to NEC; only those made with cow’s milk proteins are problematic. This includes around 80% of major brand and store-brand formulas, such as Similac and Enfamil.

Many parents whose preterm infants developed NEC after being fed by these formulas sued the manufacturers. Plaintiffs claim that manufacturers failed to warn about the risks of NEC from their cow’s milk-based formula, as per TorHoerman Law. If risks had been communicated clearly, more parents would have used breast milk, possibly preventing NEC.

In an NEC lawsuit update, the U.S. FDA called on baby formula and food companies to improve how they communicate recalls. They want companies to adopt what they call “radical transparency” to better protect infants.

Furthermore, the harmful impact of cow’s milk–based formula stems from its effects on gut microbiota. Instead of encouraging the growth of beneficial bacteria, it often leads to dysbiosis—an imbalance where harmful bacteria thrive. This imbalance increases inflammation, damages the gut lining, and weakens the intestinal barrier. These conditions make the newborn’s gut more vulnerable to infection and injury.

Donor Human Milk and Its Role

Donor human milk supports the health of premature and medically fragile infants. It closely mimics the composition of a mother’s milk and offers protective nutrients essential for growth and immunity.

A study published in PubMed showed that donor human milk is more effective than formula at reducing NEC risk in very preterm infants. It likely makes little to no difference in preventing infections or death before hospital discharge. This marked reduction demonstrates its value as a safe and effective feeding option.

Donor milk helps improve gut barrier function. It promotes a healthier intestinal lining and lowers the chance of harmful bacteria causing damage. Infants fed donor milk experience better gut permeability, which means their bodies can block harmful pathogens more effectively. This lowers their risk of developing severe infections.

The consistent evidence supports the use of donor human milk as a medically necessary intervention, not just a substitute. Its role in lowering disease risk and supporting healthy development makes it a preferred choice in clinical care for premature infants.

Adding Probiotics to the Picture

Probiotics are live microorganisms that support gut health, especially in premature infants. When introduced early, they can help build a stronger intestinal barrier and balance the gut microbiome.

A study in the Wiley Online Library suggests that probiotics may help lower the risk of NEC, sepsis, and death in preterm infants. Probiotics may also help reduce the number of days babies stay in the hospital.

Multi-strain probiotic combinations showed the most promising outcomes. Strains like Lactobacillus and Bifidobacterium work together to support digestion, strengthen the gut lining, and reduce harmful inflammation. Their combined effect enhances colonization of healthy bacteria, making it harder for pathogens to take hold in a newborn’s gut.

Probiotics should be part of a broader strategy to support infant gut health. When combined with donor human milk, they provide layered protection against intestinal diseases. This dual approach improves survival chances, especially in infants born before 32 weeks of gestation.

FAQs

How does antibiotic use in NICUs influence the effectiveness of probiotics?

Antibiotic use in NICUs can reduce the effectiveness of probiotics by disrupting the gut microbiota and killing harmful and beneficial bacteria. This interference may limit the ability of probiotics to colonize the intestines and provide their protective effects against conditions like NEC.

Is there a link between feeding type and the incidence of late-onset sepsis?

Yes, feeding type is linked to the incidence of late-onset sepsis. Breast milk, especially mother’s milk, is associated with a lower risk compared to formula feeding. It provides immune-protective factors that help reduce infection and support gut barrier function in preterm infants.

How does maternal diet impact the quality of breast milk and infant gut health?

Maternal diet directly influences the composition of breast milk, including its fatty acids, vitamins, and microbiota. A nutrient-rich, balanced diet enhances breast milk quality, which supports the infant’s gut microbiome development. It also strengthens immunity and reduces the risk of infections and inflammatory conditions.

Informed feeding decisions are critical to protecting the health and survival of vulnerable newborns. The use of human milk, donor milk, and targeted probiotics can significantly reduce the risk of necrotizing enterocolitis (NEC) and related complications.

Clinical teams must stay aligned with the latest research and guidelines to avoid preventable outcomes. By prioritizing evidence-based practices, healthcare providers can give premature and low-birth-weight infants the strongest possible start, one that supports long-term development.

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