How These Unique Substances in Breast Milk Strengthen Your Baby’s Immunity

Beyond providing essential nutrients, breast milk contains remarkable bioactive components called human milk oligosaccharides (HMOs). This article explores how these unique sugars shape infant gut health, support immunity, and influence lifelong wellbeing.

WORDS PROFESSOR DR PRAMEELA KANNAN KUTTY

FEATURED EXPERT PROFESSOR DR PRAMEELA KANNAN KUTTY Professor of Paediatrics International Medical School Management and Science University

Unique to humans in both composition and function, human milk oligosaccharides (HMOs) are special complex sugars produced by a woman whose body is producing breast milk to feed her baby (lactating mother).

These sugars provide both immediate protection and long-term support for the delicate environment of a newborn’s developing gut.

THERE ARE MANY DIFFERENT TYPES OF HMOs

So far, experts have found nearly 200 different types of special sugars in breast milk, called human milk oligosaccharides or HMOs.

These sugars are built around a core sugar called lactose and basically come in 3 main types:

• Fucosylated HMOs (which have a type of sugar called fucose attached)
• Sialylated HMOs (which have a small acidic part attached)
• Neutral HMOs (which don’t have fucose but aren’t acidic either)

Among these, the neutral HMOs are the most common, making up about two-thirds of all the HMOs in breast milk.

The most abundant of these neutral HMOs is called 2′-fucosyllactose (or 2′-FL), though how much of it is present can differ from mother to mother.

What Determines the Types of HMOs Produced by a Lactating Mother?

We’re still not sure if a mother’s unique mix of HMOs naturally changes to meet the specific needs of her baby.

But what we do know is that the amount and type of HMOs a mother produces can be influenced by two kinds of factors: ones she can’t control, and ones she can.

Non-modifiable factors

• The factors she can’t control (called non-modifiable factors) are based on her genetics, especially certain genes from what’s known as the Lewis blood group system.
• These genes, found on chromosomes 19p13.3 and 19q13.3, help decide how much of certain HMOs a mother makes.
• For example, women known as non-secretors tend to produce lower amounts of HMOs compared to secretors.

Modifiable Factors

A lactating mother can manage certain factors that can affect HMO levels; these are called modifiable factors.

These factors include:

• Her weight
• Whether she has ongoing inflammation-related health issues
• Her eating habits.
• Environment and others

THE BENEFITS OF HMOs IN BREAST MILK

HMOs Act as Prebiotics

Unlike lactose, the primary milk sugar that is digested in the small intestine, HMOs are not broken down by the infant’s digestive enzymes.

Instead, they pass largely intact into the infant’s gut, where they act as prebiotics or foods to nourish good bacteria in the gut. The infant’s gut is seeded by microbes from various sources including those that are believed to travel from a mother’s gut into her milk.

The collaboration of beneficial microbes, HMOs and other constituents in mother’s milk boost the gut milieu to favourably influence the development of the immature immune system.

As Prebiotics, They Allow Good Bacteria to Thrive in Baby’s Gut

These sugars also facilitate cross-feeding, a process where beneficial bacteria share nutrients from HMOs to strengthen the gut ecosystem and lay the groundwork for good health.

Studies show HMOs help multiple strains of Bifidobacteria grow, leading to a healthier balance of gut metabolites.

Additionally, HMOs also interact with the gut-associated lymphoid tissue (GALT), a key immune system component lining the intestines. This interaction enlivens growth of beneficial gut bacteria and fortifies gut immunity.

Healthy Good Bacteria Population in Baby’s Gut Protects Baby from Infectious Diseases

Through this, HMOs foster the growth of beneficial microbes while restricting harmful ones — a process known as colonization resistance — thus protecting the infant from gut infections and diseases.

• HMOs block harmful bacteria and viruses from attaching to the gut lining and multiplying inside the body.
• HMOs have demonstrated inhibitory effects against common potentially harmful bacteria such as Escherichia coli (E. coli), Campylobacter jejuni, Pseudomonas aeruginosa, Helicobacter pylori, and Vibrio cholerae.
• They also significantly reduce the growth of Group B Streptococcus (GBS), a bacterium that can cause serious infections in newborns.
• Furthermore, HMOs display anti-viral action against viruses such as Noroviruses, HIV, Rotavirus, and Parainfluenza virus.

HMOs Also Support Gut Defenses and Immunity

HMOs help stimulate a wide range of gut and immune system functions.

• They enhance the communication networks of gut cells.
• They strengthen both innate immunity (the body’s immediate response system) and adaptive immunity (long-term immune responses).

In addition, HMOs activate Peyer’s patches which are tiny immune structures in the intestines and stimulate B cell immunity, to pep up overall immunity.

HMOs Potentially Reduce Gut Inflammation

HMOs can do this by:

• Lowering mucosal leukocyte (white blood cell) infiltration
• Influencing the activity of intestinal cells, immune cells and their receptors
• Helping to regulate immune cell signaling molecules such as cytokines.

Such actions help fight off infections with minimal inflammation. An anti-inflammatory milieu in the gut is a foundation for health.

HMOs Support Baby’s Growth and Development

Certain HMOs have been linked directly to improved infant growth rates.

Additionally, HMOs may help regulate appetite by influencing hormones like ghrelin and leptin, further highlighting their role in early growth and energy management.

Potential Long-term Health Benefits

Thanks to their anti-inflammatory and immune-modulating properties, HMOs may be beneficial not only in infancy but also later in life.

They show promise in supporting conditions such as:

• Rheumatoid arthritis
• Inflammatory bowel disease
• Allergies
• Obesity
• Diabetes mellitus
• Cardiovascular diseases

LET’S MAKE A DIFFERENCE FOR HEALTH!

Considering all the goodness in breastmilk, we should exclusively breastfeed our children for the first 6 month and continue breastfeeding until for at least two years of age, as recommended by the Ministry of Health Malaysia.

As our children grow, we should encourage healthy lifestyles, balanced diets and regular exercise.

Under such vibrant influences, we energize the benefits described above to optimize gut health and nurture holistic wellbeing.

Health-protective compounds and the personalized dynamics in mother’s milk highlighted by the fascinating profiles of its HMOs, jumpstart this lifelong process.

References:

1. Ambalavanan, A., Chang, L., Choi, J., Zhang, Y., Stickley, S. A., Fang, Z. Y., Miliku, K., Robertson, B., Yonemitsu, C., Turvey, S. E., Mandhane, P. J., Simons, E., Moraes, T. J., Anand, S. S., Paré, G., Williams, J. E., Murdoch, B. M., Otoo, G. E., Mbugua, S., Kamau-Mbuthia, E. W., … Duan, Q. (2024). Human milk oligosaccharides are associated with maternal genetics and respiratory health of human milk-fed children. Nature communications, 15(1), 7735. https://doi.org/10.1038/s41467-024-51743-6
2. Notarbartolo, V., Giuffrè, M., Montante, C., Corsello, G., & Carta, M. (2022). Composition of human breast milk microbiota and its role in children’s health. Pediatric gastroenterology, hepatology & nutrition, 25(3), 194–210. https://doi.org/10.5223/pghn.2022.25.3.194
3. Hegar, B., Wibowo, Y., Basrowi, R. W., Ranuh, R. G., Sudarmo, S. M., Munasir, Z., Atthiyah, A. F., Widodo, A. D., Supriatmo, Kadim, M., Suryawan, A., Diana, N. R., Manoppo, C., & Vandenplas, Y. (2019). The role of two human milk oligosaccharides, 2′-fucosyllactose and lacto-N-neotetraose, in infant nutrition. Pediatric gastroenterology, hepatology & nutrition, 22(4), 330–340. https://doi.org/10.5223/pghn.2019.22.4.330
4. Bode L. (2019). Human milk oligosaccharides: Next-generation functions and questions. Nestle Nutrition Institute workshop series, 90, 191–201. https://doi.org/10.1159/000490306
5. Sun, W., Tao, L., Qian, C., Xue, P. P., Du, S. S., & Tao, Y. N. (2025). Human milk oligosaccharides: Bridging the gap in intestinal microbiota between mothers and infants. Frontiers in cellular and infection microbiology, 14, 1386421. https://doi.org/10.3389/fcimb.2024.1386421
6. Walsh, C., Lane, J. A., van Sinderen, D., & Hickey, R. M. (2022). Human milk oligosaccharide-sharing by a consortium of infant derived Bifidobacterium species. Scientific reports, 12(1), 4143. https://doi.org/10.1038/s41598-022-07904-y
7. Kutty, P. K. (2020). “Mother-Microbe-Infant-Microbe” synchrony– A mini review. Journal of Advances in Medicine and Medical Research, 136–146. https://doi.org/10.9734/jammr/2020/v32i2430761
8. Slater, A. S., Hickey, R. M., & Davey, G. P. (2025). Interactions of human milk oligosaccharides with the immune system. Frontiers in immunology, 15, 1523829. https://doi.org/10.3389/fimmu.2024.1523829
9. Orczyk-Pawiłowicz, M., & Lis-Kuberka, J. (2020). The impact of dietary fucosylated oligosaccharides and glycoproteins of human milk on infant well-being. Nutrients, 12(4), 1105. https://doi.org/10.3390/nu12041105
10. Sudarma, V., Hegar, B., Hidayat, A., & Agustina, R. (2021). Human milk oligosaccharides as a missing piece in combating nutritional issues during exclusive breastfeeding. Pediatric gastroenterology, hepatology & nutrition, 24(6), 501–509. https://doi.org/10.5223/pghn.2021.24.6.501
11. Manus, M. B., Goguen, S. K., & Azad, M. B. (2023). The protective associations of breastfeeding with infant overweight and asthma are not dependent on maternal FUT2 secretor status. Frontiers in nutrition, 10, 1203552. https://doi.org/10.3389/fnut.2023.1203552