Sorry, you need to enable JavaScript to visit this website.

What are HMOs and what do they do for babies?

5 mins


Human milk oligosaccharides (HMOs) have a high profile in infant feeding, but what are they, and what do they do? After lactose and fats, HMOs in breastmilk are one of the most common components, but only about 1% of the HMOs that a baby ingests is digested and absorbed in the gut.1,2 HMOs are a key driver in establishing a healthy community of gut bacteria in new-born babies1-3 and we now know that patterns of bacteria thrive on particular HMOs in breast milk. 4 However, HMOs are more than food for bacteria.

Human milk oligosaccharides (HMOs) are thought to reduce infections because some bacteria need to attach to the gut surface to cause disease. If HMOs are present, bacteria may combine with them instead, and pass out through the stool without disease taking hold. 2

There is also evidence that HMOs rebalance the baby’s immune system after birth, which may reduce risk of eczema, asthma or other atopic disease caused by the over-reaction of the immune system’s inflammatory response. 2,5

The different effects of Human milk oligosaccharides (HMOs) and those of simple oligosaccharides like galacto-oligosaccharides (GOS) from cows‘ milk and fructo-oligosaccharides (FOS) from plant sources, is also becoming clear. In laboratory studies, potentially disease-causing bacteria grow poorly or not at all in the presence of HMOs, while ‘good’ bacteria like Bifidobacteria thrive. 6, 7 In the presence of GOS and FOS, a range of disease-causing bacteria are able to grow.7 There is no strong evidence from research that non-HMOs (GOS/FOS) have a meaningful clinical effect on rates of infection. 8

Study of infant formula with two added HMOs*

A study which looked at infant formula with the addition of 2 HMOs* showed growth similar to WHO standards and promising respiratory infection effects

Randomised controlled trials (RCTs) have compared HMO* supplemented formulas with control formulas. In one study, a formula with 2 HMOs* added (2’FL and LNnT) was compared with a control formula, and the growth curves in both groups were similar to WHO growth standards. 9 The study also found some statistically significant differences between the groups for secondary outcomes (see results below). 9 These findings are highly promising and consistent with the known effects of HMOs derived from research on breast milk. 1,2,14 However, these secondary outcomes will need to be confirmed in further research to establish cause and effect. 

Clinical trial results of formula with two added HMOs*

Primary Outcome

  • Safe and well tolerated Normal age appropriate growth
  • Normal age appropriate growth

Secondary Outcome

  • 70% significantly reduced risk of bronchitis (p≤0.01)**
  • 55% significantly reduced risk of lower respiratory tract infection (p≤0.05)**
  • 53% significantly lower use of antibiotics(p≤0.05)†

Source: Puccio G et al. Effects of infant formula with Human Milk Oligosaccharides on Growth and Morbidity: A Randomised Multicentre Trial JPGN 2017;64: 624-631

  1. Bode L. The functional biology of human milk oligosaccharides Early Human Development 2015;91:619–622.

  2. Bode L. Human milk oligosaccharides: Every baby needs a sugar mama Glycobiology 2012;9:1147–1162.

  3. Jantscher- Krenn E and Bode L. Human milk oligosaccharides and their potential benefits for the breast-fed neonate Minerva Pediatr 2012;64:83–99.

  4. Borewicz K et al. Correlating Infant Fecal Microbiota Composition and Human Milk Oligosaccharide consumption by Microbiota of 1-Month-Old Breastfed Infants Mol Nutr Food Res 2019, 1801214.

  5. Berger A. Th1 and Th2 responses: what are they? BMJ 2000;321:424.

  6. Yu ZT et al. Utilization of major fucosylated and sialylated human milk oligosaccharides by isolated human gut microbes, Glycobiology 2013;23:1281–1292.

  7. Hoefinger JL et al. In Vitro Impact of Human Milk Oligosaccharides on Enterobacteriaceae Growth J Agric Food Chem 2015;63:3295–3302.

  8. EFSA Panel on Dietetic Products, Nutrition and Allergies EFSA Journal 2010;8(2):1430.

  9. Puccio G et al. Effects of Infant Formula With Human Milk Oligosaccharides on Growth and Morbidity: A Randomized Multicenter Trial JPGN 2017;64:624–631.

  10. Smilowitz JT et al. Breast Milk Oligosaccharides: Structure-Function Relationships in the Neonate Annu Rev Nutr 2014;34:143–169.

  11. Austin S et al. Temporal Change of the Content of Oligosaccharides in the Milk of Chinese Urban Mothers Nutrients 2016;8:346.

  12. Bode L et al. Structure-Function Relationships of Human Milk Oligosaccharides Adv Nutr 2012;3:383S–391S.

  13. Goehring KC et al. Similar to Those Who Are Breastfed, Infants Fed a Formula Containing 2’-Fucosyllactose Have Lower Inflammatory Cytokines in a Randomized Controlled Trial J Nutr 2016;146:2559–2566.