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The role of the gut microbiome in infant health and immunity

The important role of the gut microbiome in infants’ immune system development and future health is becoming ever clearer. In this article for healthcare professionals, we take a closer look at the gut microbiome, its link to overall health, and how it can be supported with specific nutritional components. 

What is the gut microbiome? 

The surface of our planet is covered in microbes, and we are no different. Microbes are found on any external surface of our body, including the skin and gut¹ and these bacterial cells are thought to number 10 to 100 times higher than our own human cells² . The combination of all the genetic information of the microbes on your body is your ‘microbiome³ . Our gut alone, in particular the large intestine, contains 1,000 known species of bacteria and is the area with the highest levels of bacteria on our body¹,⁴. 

Why is the gut microbiome important?

Through research it is becoming increasingly apparent that the gut microbiome links to overall health, particularly in the areas of digestion and absorption of nutrients, gut-brain interactions and immunity⁵,⁶. Bacteria digest fibres, in the large intestine, and this leads to production of important metabolites e.g. short chain fatty acids (SCFA)⁷. SCFAs are estimated to contribute 10% of energy requirements⁸, highlighting the microbiome’s important role in extracting nutrients from our diet. 

70-80% of the body’s immune cells are in the gut and the bacteria in the gut communicate with these cells, therefore the gut microbiome provides the most important stimulation source for developing immunity⁹,²⁰. In relation to immunity, studies have found links between gut microbiome and allergy incidence, e.g. caesarean infants, who had a different microbiome composition to vaginal delivered infants, were found to have increased cytokine IL-13 production suggesting higher asthma incidence¹⁰.

How does the gut microbiome develop? 

The gut microbiome develops rapidly in early years, reaching adult-like composition by around 3 years of age¹¹. The early years of life are a crucial period to support development of a healthy microbiome and can be influenced by environmental factors including: mode of delivery (e.g. vaginal or c-section), gestational age at birth and diet¹². Early life nutrition is an important factor, influencing the development of the gut, microbiome and immune system². 

Breastmilk is the best nutrition for newborns and has been shown to support optimal growth and development of infants. Exclusive breastfeeding is widely recommended as the first choice for infant nutrition¹³. Breastmilk has a highly diverse range of components, including human milk oligosaccharides (HMOs), live bacteria and their metabolites¹⁴,¹⁵. These are acknowledged to play a crucial role in the development of the gut microbiome and immune system¹⁶. 

Specific nutritional components can support a healthy gut microbiome. These include probiotics, prebiotics, synbiotics and postbiotics. 

Quick definitions:

  • Prebiotics are substrates that pass to the gut where they stimulate the growth or activity of beneficial bacteria¹⁷
  • Probiotics are beneficial bacteria that affect the host microbiome when ingested in adequate amounts¹⁸
  • Synbiotics are a combination of prebiotics and probiotics¹⁸
  • Postbiotics are bioactive compounds produced by beneficial bacteria, which have biological activity in the host¹⁸
  • Human milk oligosaccharides (HMOs) are a complex pool of carbohydrates that exist in high levels in human milk, with prebiotic and other important benefits¹⁹

In summary

The importance of the gut microbiome towards an infant’s overall health has become more apparent over recent years and is likely to continue in this direction in the future. It is clear that early life is a critical period for the development of the infant gut microbiome and that nutrition is a major factor in which to help this development. 

To download and print this guide on the gut microbiome, click here.

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IMPORTANT NOTICE: Breastfeeding is best for babies. Infant formula is suitable from birth when babies are not breastfed. Follow-on milk is only for babies over 6 months, as part of a mixed diet and should not be used as a breastmilk substitute before 6 months. We advise that all formula milks including the decision to start weaning should be made on the advice of a doctor, midwife, health visitor, public health nurse, dietitian, pharmacist or other professional responsible for maternal and child care. Foods for special medical purposes should only be used under medical supervision. May be suitable for use as the sole source of nutrition for infants from birth, and/or as part of a balanced diet from 6–12 months. Refer to label for details.


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