HMOs in Infant Formula: What They Are, What They Aren’t, and Why Breastmilk Still Can’t Be Replicated

Human milk oligosaccharides — HMOs — are complex sugars found naturally in breastmilk. They are the third most abundant solid component in your milk, after lactose and fat — present in higher quantities than protein. That alone tells you how important they are.

HMOs are not digested by your baby. That might seem strange, but it is the point: they pass through the stomach and small intestine intact, arriving in the large intestine where they act as food for specific beneficial bacteria — particularly Bifidobacterium infantis, which dominates the gut of healthy breastfed babies. This is why the gut microbiome of breastfed infants looks so distinctly different from that of formula-fed infants, and why researchers consider this one of the most important functional differences between the two.

Beyond their prebiotic role, HMOs are also understood to:

• Act as decoys that block pathogens from attaching to the gut lining — essentially trapping harmful bacteria before they can cause harm
• Support immune system development and modulation in the early weeks of life
• Contribute to brain and cognitive development, with some HMOs found specifically in the neural tissue of infants
• Change dynamically throughout the course of lactation — with particularly high concentrations in colostrum — to meet your baby’s shifting developmental needs

The scale of this diversity is worth pausing on. Scientists have identified more than 200 structurally distinct HMO molecules in human milk. Every mother’s HMO profile is different, shaped by her genetics, the stage of lactation, her gut microbiome, her geography, and more. Colostrum — the milk made in the first days — contains up to 25 grams of HMOs per litre. Mature milk contains around 10–15 g/L. The composition shifts continuously across weeks and months, with some HMO types declining and others increasing as your baby grows.

Historically, infant formula contained no HMOs at all. In recent years, manufacturers have begun adding synthetically produced versions of specific HMOs to some formulas. In Australia, Food Standards Australia New Zealand (FSANZ) has progressively approved several of these for use, and a current application — Proposal A1339 — seeks to expand the approved list further.

The most commonly added synthetic HMO is 2’-fucosyllactose (2’-FL), which is one of the most abundant HMOs in most mothers’ milk. It is produced commercially through a fermentation process using non-pathogenic laboratory strains of microorganisms. After fermentation, the HMO is separated, purified, and dried before being incorporated into formula at specified levels.

FSANZ assesses these ingredients for safety before approving their use, and the weight of clinical evidence to date finds them to be safe and well-tolerated. Studies suggest that adding 2’-FL to formula may shift some infant gut microbiome outcomes in a direction more similar to breastfed infants, and some trials have observed modest improvements in immune markers.

This is genuinely positive news for families who are formula-feeding. If formula must be used, formulas that include evidence-backed HMOs may offer some functional benefit over those that do not.

But — and this is where the honest reading of the evidence matters — the marketing language of ‘breast milk identical’ significantly overstates what adding one or a handful of HMOs to formula achieves. Understanding why requires understanding just how wide the gap still is.

200 vs 5: The complexity problem

Breastmilk contains over 200 structurally distinct HMO molecules. Current leading infant formulas contain at most 5 or 6. Scientists themselves acknowledge this directly: even a five-HMO formula ‘is far from the natural abundance of nearly 200 HMOs present in human milk’. Each HMO has a unique structural identity that corresponds to a specific functional role in the infant gut and immune system. Adding a handful of them — even the most abundant ones — does not replicate the full orchestra.

Regulatory approvals by FSANZ and the European Food Safety Authority (EFSA) acknowledge this explicitly: approval of synthetic HMOs in formula is based on safety assessment, and does not constitute confirmation of health benefits equivalent to breastmilk. The First Steps Nutrition Trust, an independent UK nutrition charity, notes that regulatory approvals ‘relate only to safety and do not imply any benefits’.

The dynamic problem: your milk is not a fixed recipe

Breastmilk is a living biological fluid that changes constantly. It changes from feed to feed. It changes hour to hour across the day. It changes week to week as your baby grows. Colostrum has a completely different composition from mature milk. Late-lactation milk looks different again. Your HMO profile shifts to match what your baby needs at each stage of development.

Infant formula is, by its nature, a fixed composition. However sophisticated the formulation, it cannot respond in real time to your baby’s cues, developmental stage, or current immune status the way your own milk does. This adaptive quality is one of the most fundamental differences between breastmilk and any engineered substitute.

Breastmilk is alive in a way formula cannot be

Beyond HMOs, breastmilk contains components that have no formula equivalent at all. Recent research describes human milk as a ‘dynamic, living fluid packed with cells, bioactive molecules, and a complex microbiome’. This includes:

• Living immune cells — including macrophages, lymphocytes, and neutrophils — that actively respond to pathogens the baby encounters. When your baby is unwell, the white cell content of your milk increases in real time
• Stem cells that can cross the infant’s gut wall, enter the bloodstream, and reach distant organs — research is still exploring what role these play in tissue development and immune programming
• Secretory IgA antibodies that are specific to the pathogens in your environment and your baby’s environment — antibodies that formula cannot contain because they do not exist outside a living body
• Hundreds of bioactive proteins, hormones, enzymes, growth factors, and cytokines that regulate inflammation, support organ development, and shape gut maturation
• A living microbiome — your milk contains bacteria that colonise your baby’s gut and are shaped by your own gut health and environment

None of these components are present in infant formula — not because manufacturers haven’t tried to include them, but because they are products of a living body responding to a living baby, and cannot be engineered or shelf-stabilised. HMOs are an important piece of what makes breastmilk exceptional, but they are one thread in an extraordinarily complex tapestry.

For the full picture of breastfeeding nutrition, return to our pillar guide: Breastfeeding Nutrition & Milk Supply: Evidence-Based Guide for Australian Mothers.

If this article has prompted questions about supporting your own breastfeeding journey, these related guides may help:

• 10 Proven Ways to Increase Your Milk Supply — evidence-based strategies when supply is a concern
• Foods That Actually Increase Milk Supply: The Evidence — what the research says about nutrition and galactagogues
• Natural Electrolyte Drinks for Breastfeeding Mums — nourishing the source with the right hydration
• Formula vs Breastmilk for Babies with Eczema — navigating feeding decisions when your baby has sensitive skin
• The Benefits of Fenugreek for Breastfeeding — what the evidence says about one of the most commonly used galactagogues
• Best Lactation Cookies in Australia: What Actually Works — evidence-aligned lactation support products for Australian mums

Supporting your body well through breastfeeding — with good nutrition, adequate hydration, and the right support — is the most direct way to invest in the remarkable, irreplaceable milk your body makes. Explore our lactation support range, formulated by a Certified Postpartum Nutrition Professional for exactly this stage of motherhood.