Human Milk Oligosaccharides: What Are HMOs And Why Do They Matter?

March 8, 2023

Human milk oligosaccharides (HMOs) are special milk sugars found in breastmilk. The key thing to understand about HMOs is that we cannot digest them. But good gut bacteria can.


This means that HMOs act as a prebiotic in the gut, helping beneficial communities of bacteria thrive.

HMOs support baby gut health

It’s estimated that there are more than 200 different types of HMOs1. After lactose and fat, HMOs are the third most abundant component of breastmilk. In other words, the sheer volume of these special sugars in breastmilk lets us know how important they are to baby health.


There are a couple of ways that HMOs support baby gut health.


1. Human milk oligosaccharides increase levels of good gut bacteria.


As we mentioned earlier, HMOs act as a prebiotic. This means that they feed a baby’s good gut bacteria, such as Bifidobacterium2 and Bacteroides3.


As bacteria feed on HMOs, they produce short-chain fatty acids (SCFA), which are equipped with their own set of benefits.


For example, SCFAs help to:

●     Maintain gut integrity

●     Produce protective mucus that lines the gut wall

●     Protect against inflammation4


As it turns out, one way to measure a baby’s immune strength is to check levels of friendly, HMO-digesting species with baby gut testing.


2. HMOs directly influence the immune system. For example, they can help reduce the risk of viral and bacterial infections5.


We also know thatHMOs can stop the growth of Streptococcus agalactiae, a bacteria that’s also known as group B Streptococcus or GBS. Likewise, breastmilk has been shown to protect against rotavirus6.


Research also shows that HMOs also have the ability to:

●     Change intestinal cells programmed for cell death, also known as apoptosis

●     Alter gene expression in certain cells7

●     Reduce levels of disruptive and unfriendly microbes

How to get HMOs when formula is your only option

Fortunately, the value of human milk oligosaccharides has not gone unnoticed by infant formula manufacturers.


The HMO that you will most often see added to formula is 2’-FL.


While HMO levels are significantly lower than what you would find in breastmilk, there are still benefits. For example, studies suggest that babies fed infant formula containing 2′-FL have an anti-inflammatory response that’s similar to breastfed babies8.


Still, if breastmilk is available, this is the better option.


This is because breastmilk contains varying levels of HMOs at different points in time. Colostrum, the first breastmilk that comes in after birth, is especially rich in HMOs. Levels go as high as 20.0g/L, while mature milk only has 12.9 g/L9.


In contrast, formula only provides a small amount of HMOs and these levels do not change according to a baby’s age or the stage of formula that’s used.

Track HMO-digesting bacteria with baby gut testing

To track whether breastmilk or yourHMO-boosted formula can support levels of good gut bacteria, you may want to run a Tiny Health baby gut test.


Fortunately, microbiome testing can reveal which bacteria are thriving (beneficial or unfriendly). And whether or not HMO-digesting species, such as Bifidobacterium, need extra support.


  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. 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.
  3. 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.
  4. Y. P. Silva, A. Bernardi, and R. L. Frozza, “The Role of Short-Chain Fatty AcidsFrom Gut Microbiota in Gut-Brain Communication,” Front. Endocrinol., vol. 11, 2020, doi: 10.3389/fendo.2020.00025.
  5. 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.
  6. 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.
  7. R. Akkerman, M. M. Faas, and P. de Vos, “Non-digestible carbohydrates in infant formula as substitution for human milk oligosaccharide functions: Effects onmicrobiota and gut maturation,” Crit. Rev. Food Sci. Nutr., vol. 59, no. 9, pp. 1486–1497, 2019, doi: 10.1080/10408398.2017.1414030.
  8. 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 Containing2’-Fucosyllactose Have Lower Inflammatory Cytokines in a Randomized ControlledTrial,” J. Nutr., vol. 146, no. 12, pp. 2559–2566, Dec. 2016, doi: 10.3945/jn.116.236919.
  9. 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.