Breastfeeding and the microbiome

The British Nutrition Foundation recently gave a webinar on the benefits of breastfeeding for the infant’s microbiome. The following speakers spoke about the latest research and understanding in this area: Helena Gibson-Moore, British Nutrition Foundation , Prof Christine Edwards, University of Glasgow , Prof Lars Bode, University of California, San Diego and Dr Ruairi Robertson, Queen Mary University of London & University of British Columbia.

In the UK 80% of mothers start breastfeeding, but by 6 months only 1% are still doing it. Many mothers know that there are benefits for both mother and baby of breastfeeding, but for many reasons may either struggle to establish breastfeeding, find it hard to maintain or choose not to start or continue. Reasons are many and varied and there is always a need for greater postnatal support.

Breastfeeding can be a sensitive subject for many and this blog isn’t about adding further guilt to those who have struggled to breastfeed. I am simply sharing this new and exciting area of research. Perhaps seeing how amazing and complex breastmilk is will help someone who is undecided about breastfeeding or needs faith to continue. For those that struggle I am happy to say that Exeter has some amazing peer support groups and lactation consultants and I would urge you to seek help and advice asap and not struggle at home alone. The Baby Room in Exeter has several welcoming groups (their website is here) and Jen and Gillian who run it can point you in the right direction of further support if you need it.

 So, let’s talk breastmilk. Breastmilk contains hundreds of bioactive compounds - these are types of chemicals which have clever roles in the body and can do us good. Some of these compounds are known to promote good bacteria in the gut.

When it comes to gut microbes - the more diverse the better. When a baby is born their gut is sterile and over the next days and weeks the bacteria the baby comes into contact with starts populating their gut and teaching their immune system how to deal with it’s environment. A vaginal birth is known to help the baby by exposing it to lots of beneficial bacteria from the mothers gut. The skin to skin contact of breastfeeding also helps the baby ingest bacteria from the mothers skin.

Within the breastmilk itself there are compounds that help promote good bacteria and minimise undesirable bacteria. Some of these are:

  • Lactoferrin which binds iron, so that there is less for bad bacteria to use (without iron they will die)

  •  Oligosaccharides  (>150 different types) which are known to promote the friendly bacteria bifidobacteria 

  • Antibacterial factors -  such as antibodies and enzymes which stop the growth of less preferable bacteria

  • Bacteria in the breastmilk – may help establish bacteria in gut (need more studies).  These change over time and are affected by the mothers own bacteria, for example it is known that people who are overweight have less diverse strains of bacteria, which is another reason why eating well before you even get pregnant can benefit the baby.


Interestingly it has been shown that breastfeeding and providing these compounds even at 1 year (alongside solid foods) continues to benefit the child, so continuing breastfeeding alongside weaning will provide things the rest of the diet or formula can’t.

The focus of much research has been on the oligosaccharides which have a prebiotic effect and feed the good bacteria in the gut, thereby producing Short Chain Fatty Acids (SCFA) which effect satiety, metabolism, gut integrity, reduce colonic pH, inhibit pathogens and help with vitamin production.

There are hardly any oligosaccharides in formula. Plus, with formula fed babies it has been shown that the reduced amounts of lactic acid in the formula promote different bacteria which produce SCFAs earlier in the babies life. It is unknown what the impact of this is on long term health.


Human Milk Oligosaccharides (HMOs) are complex sugars. There are  150 – 200 different types and every Mum makes different ones and different amounts of each one (like her own milk fingerprint).

Many factors drive the differences in HMO composition between mothers:

  • Genetics

  • Diet

  • Probiotics

  • Drugs

  • Physical activity

  • Timing – lactation stage, maternal age, parity (first child?)

  • Maternal health


What are the benefits of HMOs?

  1. Most HMOs are degraded in colon and therefore reach the gut microbiome.

  2. They are Prebiotic (enrich good bacteria) and different HMOs promote different bacteria

  3. They have an anti-adhesive effect by stopping bad bacteria binding to the gut these pathogens get washed out

  4. Antibacterial

  5. They have an effect on the immune system, changing the gut lining cell response.

  6. The more diverse these HMOs the less fat mass the infant has at 1 month and they seem to have protective effects against stunting and better bone formation


These benefits will impact the child over their entire lifespan, therefore having implications for health throughout adulthood and old age, as well as being handed down to their offspring.

The mechanisms and importance of the role of HMOs is still under investigation, but it is clear that they are doing something that is benefiting the gut microbiome and as research continues to shed light on the many roles these bacteria have in our body, doing what we can to help them out is super important.

When we think of breastmilk, we tend to think about it as food, helping the baby to grow, which is something formula can achieve just as well. What is interesting to consider is the role breastmilk also has in teaching our immune systems to deal with the environment and helping our organs to develop complex systems. Formula is unable to replicate these complex bioactive compounds and the variety that is present in human milk.

Human milk also continually changes throughout the babies development, changing during a feed and over the course of the day, so provide the baby with a bespoke feed. I am always in awe of what our bodies are able to do when it comes to reproducing! So, if you can breastfeed and get the support you need to continue then you can be sure it is worth the effort.



Ruth Harvey