What Are Human Milk Oligosaccharides (HMOs)?


  • HMOs are a type of milk sugar found in mom’s breastmilk.
  • HMOs go undigested through your baby's digestive tract and feed your baby’s gut microbes.
  • HMOs can reduce the risk of viral and bacterial infections and help develop your baby’s immune system.
  • Some infant formulas now contain HMOs, but breastmilk may still be a better option.

Human milk oligosaccharides, or simply HMOs, are milk sugars that are found in your breastmilk. Breastmilk contains more than 200 different types of HMOs [1]. Just like a fingerprint, your HMO profile is unique.

HMOs are a chemical variation of the milk sugar, lactose. All HMOs are made up of a combination of  smaller sugars, which includes:

  • Glucose
  • Galactose
  • Fucose
  • N-acetylglucosamine (GlcNAc)
  • Sialic acid (N-acetylneuraminic acid) sugars [2]

After lactose and fats, HMOs are the third most abundant component of breastmilk. The most abundant HMO in the majority of a mother’s breast milk is 2′-fucosyllactose (2′-FL) [3].

2′-fucosyllactose (2′-FL) is made up of the combination:

  • Glucose
  • Galactose
  • Fucose [3]

HMOs will often differ in the presence or absence of the sugar molecule fucose. This is because 97% of moms have an active gene for fucosyltransferase (FUT2) The enzyme FUT2 makes sure that the sugar fucose is part of breastmilk sugars [2].

Though HMOs are present in your breastmilk, they do not provide nutrition for your baby. This is because HMOs go undigested through your baby's digestive tract [4]. But this is good. This feeds your baby’s gut microbes.

The benefits of human milk oligosaccharides (HMOs)

1. HMOs increase beneficial bacteria

Even though your baby can’t digest HMOs, certain beneficial gut bacteria can. HMOs provide energy for beneficial bacteria, such as members of the Bifidobacterium and Bacteroides genera [5], [6]. These beneficial bacteria feed on HMOs through a process called fermentation.

Bacteria ferment HMOs and produce beneficial by-products called short-chain fatty acids (SCFA). SCFA are metabolites that have been shown to improve gut health by helping:

  • Maintain gut integrity
  • Produce mucus
  • Protect against inflammation [7]

This explains why the gut microbiome of breastfed babies is dominated by Bifidobacterium [2]. Breastmilk contains high levels of HMOs that Bifidobacterium are able to ferment.

2. HMOs improve your baby’s immune system

Because HMOs reduce the risk of viral and bacterial infections, they can directly influence your baby's immune system.

Research has shown that HMOs improve your babies immune system by helping:

  • Fight unfriendly microbes
  • Change intestinal cells programed for cell death, also known as apoptosis
  • Alter gene expression in certain cells [8]
  • Reduce unfriendly microbes

Apart from helping boost your baby's immune system, HMOs can also directly affect unfriendly microbes. HMOs have been found to have a unique antibacterial or antiviral role against certain microbes [9].

This can be seen with Streptococcus agalactiae, also called group B Streptococcus or GBS, which is an important unfriendly gut bacteria for babies. HMOs have been found to stop the growth of these bacteria [9].

Similarly, breastmilk has been shown to protect against rotavirus in babies aged 0 to 12 months [10]. Rotavirus causes watery diarrhea and vomiting in babies.

HMOs and infant formula

The importance of HMOs to your baby's gut microbiome is so great that infant formula companies have now started to include them. The most common HMOs you will see added to infant formula are:

  • 2’ -fucosyllactose (2’-FL)
  • lacto-N-neotetraose (LNnT)

These two HMOs differ in the presence or absence of the specific sugar molecule, fucose.

Research has shown that babies fed an infant formula containing 2′-FL have an anti-inflammatory response that’s similar to breastfed babies [11].

Some infant formula brands that contain HMOs include:

  • Abbot’s Similac Pro-Advance Infant Formula
  • Enfamil NeuroPro Infant

Breastmilk HMOs vs Infant formula HMOs

Although some infant formulas now contain HMOs, breastmilk may still be a better option, if it is an option. It’s free. It’s natural. It’s your own.

Apart from breastmilk adjusting to provide the right amount of nutrients for your baby, it also contains different amounts of HMOs at different time points. This can be seen in colostrum, the first breastmilk after birth, which is especially rich in HMOs. Levels go  as high as 20.0g/L, while mature milk only has 12.9 g/L [12].

In contrast, infant formula only provides a very small proportion of HMO compared to breastmilk.

While manufacturers of infant formulas produce a product that is increasingly similar to breastmilk, the gut microbiota of breastfed and formula-fed babies still remains very different [13].

That said, whether you feed your baby formula, breastmilk, or a combination of the two– HMOs can help your baby's gut microbiome along the way!


[1] N. J. Andreas, B. Kampmann, and K. Mehring Le-Doare, “Human breast milk: A review on its composition and bioactivity,” Early Hum. Dev., vol. 91, no. 11, pp. 629–635, Nov. 2015, doi: 10.1016/j.earlhumdev.2015.08.013.

[2] M. Wiciński, E. Sawicka, J. Gębalski, K. Kubiak, and B. Malinowski, “Human Milk Oligosaccharides: Health Benefits, Potential Applications in Infant Formulas, and Pharmacology,” Nutrients, vol. 12, no. 1, p. E266, Jan. 2020, doi: 10.3390/nu12010266.

[3] E. J. Reverri, A. A. Devitt, J. A. Kajzer, G. E. Baggs, and M. W. Borschel, “Review of the Clinical Experiences of Feeding Infants Formula Containing the Human Milk Oligosaccharide 2′-Fucosyllactose,” Nutrients, vol. 10, no. 10, Oct. 2018, doi: 10.3390/nu10101346.

[4] R. E. Moore and S. D. Townsend, “Temporal development of the infant gut microbiome,” Open Biol., vol. 9, no. 9, p. 190128, Sep. 2019, doi: 10.1098/rsob.190128.

[5] D. A. Sela and D. A. Mills, “Nursing our microbiota: molecular linkages between bifidobacteria and milk oligosaccharides,” Trends Microbiol., vol. 18, no. 7, p. 298, Jul. 2010, doi: 10.1016/j.tim.2010.03.008.

[6] A. Marcobal et al., “Bacteroides in the infant gut consume milk oligosaccharides via mucus-utilization pathways,” Cell Host Microbe, vol. 10, no. 5, pp. 507–514, Nov. 2011, doi: 10.1016/j.chom.2011.10.007.

[7] Y. P. Silva, A. Bernardi, and R. L. Frozza, “The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication,” Front. Endocrinol., vol. 11, 2020, doi: 10.3389/fendo.2020.00025.

[8] R. Akkerman, M. M. Faas, and P. de Vos, “Non-digestible carbohydrates in infant formula as substitution for human milk oligosaccharide functions: Effects on microbiota and gut maturation,” Crit. Rev. Food Sci. Nutr., vol. 59, no. 9, pp. 1486–1497, 2019, doi: 10.1080/10408398.2017.1414030.

[9] A. E. Lin et al., “Human milk oligosaccharides inhibit growth of group B Streptococcus,” J. Biol. Chem., vol. 292, no. 27, pp. 11243–11249, Jul. 2017, doi: 10.1074/jbc.M117.789974.

[10] A. Plenge-Bönig, N. Soto-Ramírez, W. Karmaus, G. Petersen, S. Davis, and J. Forster, “Breastfeeding protects against acute gastroenteritis due to rotavirus in infants,” Eur. J. Pediatr., vol. 169, no. 12, pp. 1471–1476, Dec. 2010, doi: 10.1007/s00431-010-1245-0.

[11] K. C. Goehring, B. J. Marriage, J. S. Oliver, J. A. Wilder, E. G. Barrett, and R. H. Buck, “Similar to Those Who Are Breastfed, Infants Fed a Formula Containing 2’-Fucosyllactose Have Lower Inflammatory Cytokines in a Randomized Controlled Trial,” J. Nutr., vol. 146, no. 12, pp. 2559–2566, Dec. 2016, doi: 10.3945/jn.116.236919.

[12] L. Bode, “Human milk oligosaccharides: every baby needs a sugar mama,” Glycobiology, vol. 22, no. 9, pp. 1147–1162, Sep. 2012, doi: 10.1093/glycob/cws074.

[13] A. M. Baumann-Dudenhoeffer, A. W. D’Souza, P. I. Tarr, B. B. Warner, and G. Dantas, “Infant diet and maternal gestational weight gain predict early metabolic maturation of gut microbiomes,” Nat. Med., vol. 24, no. 12, pp. 1822–1829, Dec. 2018, doi: 10.1038/s41591-018-0216-2.