As lactation professionals, we know that optimal infant nutrition is not just about calories—it’s about timing, composition, and individual physiology. Human milk is the gold standard for all infants, but the nutritional needs of a term infant are not the same as those of a preterm infant. This post explores the dynamic nature of human milk, how it differs from infant formula, and how lactation consultants can provide evidence-based support to meet the specific nutritional needs of both term and preterm infants.

Human Milk: A Living, Dynamic Fluid

Human milk is uniquely and biologically tailored to meet the needs of human infants. It is not a static fluid. Its composition shifts throughout the day, across the course of a feeding, and over the weeks and months of lactation. Unlike artificial infant formula, which is manufactured to a fixed composition, human milk responds to:

• The infant’s age and developmental stage

• Time of day (e.g., nighttime milk has more melatonin and fat)

• Duration within a single feeding (foremilk vs. hindmilk)

• Illness or immune signaling from the infant

Human milk provides:

• Macronutrients: Lactose (7 g/100 mL), fat (3.5–4.5 g/100 mL), and protein (0.8–1.2 g/100 mL in mature milk)

• Micronutrients: Highly bioavailable forms of vitamins and minerals

• Immune factors: Secretory IgA, lactoferrin, lysozyme, cytokines, leukocytes, and human milk oligosaccharides (HMOs)

• Hormones and enzymes: Leptin, ghrelin, insulin, lipase, and growth factors

• Microbiota-shaping elements: HMOs that selectively feed beneficial gut bacteria

These bioactive and immune components are absent or significantly diminished in infant formula. While formula manufacturers attempt to replicate the basic macronutrient profile of breast milk, they cannot replicate its living complexity or ability to adapt to an individual infant.

Term Infant Nutrition: Physiologic Norms

Term infants (born ≥37 weeks) are developmentally prepared for extrauterine life. Their gastrointestinal systems are mature enough to digest and absorb nutrients from human milk efficiently. Term milk supports:

• Growth: With energy density around 67–70 kcal/100 mL, term infants typically gain ~20–30 g/day.

• Immune development: Colostrum and early milk are rich in sIgA and leukocytes, seeding the infant’s immune system.

• Neurodevelopment: Long-chain polyunsaturated fatty acids (DHA, ARA) in milk are essential for brain and retinal development.

Breastfeeding is both nutrition and protection. Term infants fed exclusively human milk generally do not require supplementation unless specific risk factors are present.

Growth Trajectories in Term Infants

Breastfed term infants grow differently than formula-fed infants:

• Breastfed infants tend to gain weight more slowly after the first two months, with leaner body composition and slower fat gain.

• Formula-fed infants tend to grow faster and have higher adiposity in the first year, potentially contributing to higher long-term risks of obesity, metabolic syndrome, and type 2 diabetes.

These differences are physiologically normal and expected. The WHO growth charts, based on breastfed infants, are the preferred standard for evaluating term infant growth.

Preterm Infant Nutrition: Bridging the Gap

Preterm infants (<37 weeks gestation) are born during a time when rapid in utero growth and nutrient accretion would normally occur—especially for brain and bone development. They are at high risk for:

• Postnatal growth restriction

• Osteopenia of prematurity

• Feeding intolerance

• Necrotizing enterocolitis (NEC)

Their nutritional needs are significantly higher than those of term infants:

• Energy: ~110–140 kcal/kg/day

• Protein: ~3.5–4.5 g/kg/day (compared to ~1.5–2 g/kg/day for term infants)

• Calcium and phosphorus: To support skeletal growth

• Zinc, sodium, and vitamins A, D, and E: To meet metabolic demands

Even though preterm milk is more nutrient-dense than term milk—particularly in protein and minerals—it still does not meet the full requirements of very low birth weight (VLBW) infants when given alone.

Why Are Preterm Infant Nutritional Needs Higher?

The heightened nutritional needs of preterm infants stem from multiple biological and developmental factors:

1. Interrupted Third Trimester Nutrient Accretion

The third trimester is a period of rapid intrauterine growth and nutrient accumulation. During this time, fetuses accrue:

• Calcium and phosphorus for bone mineralization

• Iron and zinc for hematologic and immune system development

• Fat and protein stores for energy and tissue building

• Long-chain polyunsaturated fatty acids (DHA and ARA) for brain and retinal development

When infants are born early, this critical period of nutrient transfer is cut short. Preterm infants must now achieve similar accretion rates outside the womb, with less physiological efficiency and more metabolic demands.

2. Higher Growth Velocity

Compared to term infants, preterm infants require faster growth rates to match their expected intrauterine growth trajectory. This means:

• More energy per kilogram is required to fuel both maintenance and rapid tissue synthesis.

• More protein per kilogram is needed to support neurodevelopment and lean body mass.

• Failure to meet these needs can lead to postnatal growth restriction, which is associated with poorer neurocognitive outcomes, shorter stature, and long-term health risks.

3. Immature Digestive and Metabolic Systems

Preterm infants have:

• Reduced digestive enzyme activity

• Limited bile salt production

• Immature renal function

• Altered insulin sensitivity

These limitations reduce their capacity to digest and absorb nutrients efficiently. As a result, they require more nutrient-dense feedings to compensate for their decreased absorption and increased losses.

4. Higher Risk of Illness and Stress

Preterm infants are more susceptible to:

• Sepsis

• Respiratory distress

• Feeding intolerance

• Necrotizing enterocolitis (NEC)

These conditions increase metabolic demands. Recovery and healing require additional energy and protein to support immune function, tissue repair, and thermoregulation—further increasing nutritional requirements.

5. Minimal Energy Reserves

Unlike term infants, who have subcutaneous fat stores and glycogen reserves, preterm infants are born with minimal energy and nutrient reserves. They are highly reliant on exogenous intake to meet even their basic needs, leaving little margin for delay or inadequate feeding.

Why Fortification Is Essential

To close this nutritional gap, human milk for preterm infants is routinely fortified. Human milk fortifiers (HMFs) add concentrated protein, calories, and micronutrients to expressed milk, ensuring infants achieve:

• Appropriate lean mass gain

• Optimal neurodevelopmental outcomes

• Sufficient bone mineralization

Historically, most fortifiers have been bovine milk-based. However, research indicates potential benefits of human milk-derived fortifiers in preserving immunological integrity and reducing the risk of NEC.

A 2025 network meta-analysis found that mother’s own milk supplemented with donor milk and human-milk-based fortifier ranked highest for outcomes including mortality, NEC, and time to full feeds. These findings underscore that an exclusive human milk diet—including fortifier—is associated with better outcomes than bovine-based regimens.

Fortification Strategies

There are two primary methods of fortification:

• Standard fortification – A fixed dose of fortifier added based on assumed average milk content.
• Targeted or individualized fortification – Uses milk analyzers to assess actual macronutrient content, enabling personalized supplementation.

Individualized fortification has been associated with better growth outcomes and reduced incidence of postnatal growth failure, though it requires more resources and staff training.

Comparing Nutritional Needs

Clinical Implications for Lactation Professionals

Lactation consultants have a critical role in supporting both term and preterm infants:

For term infants:

• Support exclusive breastfeeding.

• Educate about normal growth patterns.

• Reassure families about slower weight gain in breastfed infants.

For preterm infants:

• Support early milk expression and volume establishment.

• Collaborate with NICU teams on fortification plans.

• Help families transition from gavage to at-breast feeding.

• Monitor growth and feeding readiness after discharge.

• Reinforce the continued importance of human milk beyond the NICU.

Understanding the science behind human milk and preterm nutrition equips us to better advocate for individualized feeding plans, promote breast milk use even in complex cases, and ensure vulnerable infants are given the best possible start.

Final Thoughts

Human milk is more than food—it is a biologically active, responsive substance tailored to the specific needs of infants. For term babies, it provides perfect, self-adjusting nutrition. For preterm babies, it forms the foundation of a carefully fortified, lifesaving feeding plan.

By appreciating the differences in nutritional needs between term and preterm infants—and understanding the powerful adaptability of human milk—lactation professionals can provide informed, compassionate, and effective care across a wide range of clinical settings.

References

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Embleton, N. D., Moltu, S. J., Lapillonne, A., van Goudoever, J. B., & Carnielli, V. P. (2022). Enteral nutrition in preterm infants: Guidelines from the European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN). Journal of Pediatric Gastroenterology and Nutrition, 75(3), 432–447.

Rechtman, D. J., Lee, M. L., & Berg, H. (2007). Effects of a human milk-derived human milk fortifier on the antibacterial actions of human milk. Breastfeeding Medicine, 2(4), 205–211. https://DOI: 10.1089/bfm.2007.0015

Chinnappan, S., van den Akker, C. H. P., Kuschel, C. A., & Bloomfield, F. H. (2021). Bovine milk-based fortifiers and severe morbidity in very preterm infants: A retrospective cohort study. JAMA Pediatrics, 175(2), e205134. https://DOI: 10.1093/tropej/fmac110

Bollani, L., De Felice, C., & Roggero, P. (2024). Targeted fortification of human milk: Update and perspectives. In Human Milk and Lactation: Physiological Basis and Clinical Applications. Springer.

Young, B. E., & Krebs, N. F. (2020). Nutritional needs of the preterm infant. In A. E. Suchy, R. A. Heyman, & R. A. Rudolph (Eds.), Pediatric Nutrition Handbook (8th ed., pp. 87–108). American Academy of Pediatrics.

Koletzko, B., Poindexter, B., & Uauy, R. (Eds.). (2021). Nutrients in Human Milk: Comparative and Nutritional Aspects. Nestlé Nutrition Institute Workshop Series, vol. 87. Karger.

Lawrence, R. A., & Lawrence, R. M. (2022). Breastfeeding: A guide for the medical profession (9th ed.). Elsevier.

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