What are Prebiotics & Probiotics and how do they relate to the gut microbiota?

We’ve known for a long time now that the human gut contains bacteria, but it’s really only been in the last decade or so that scientists have come to appreciate how important these bacteria are to our health. For example, in babies they are known to have beneficial immunological and developmental effects.

The human gut supports trillions of bacteria. In fact, there are more bacteria in the gut than there are cells in the whole body! A healthy gut bacteria population (called the microbiota) is one with a diverse mix of bacteria types, including ‘good’ and some ‘bad’ ones.

The development of the microbiota in babies

Before birth, an infant’s gut is essentially sterile (ie. germ free). The first contact with bacteria probably occurs when babies pass through the birth canal and enter the world, however there is now some evidence to suggest it may occur even earlier (you can read more about this here).

Within a few days of birth, bacteria ‘colonise’ the gut and establish a thriving community.1 Lots of changes occur in the gut bacteria profiles during the first year of life, but by around 12 months of age most babies have a gut bacteria population that broadly resembles that of an adult.1

The development of the gut microbiota varies from baby to baby and from month to month, but it tends to follow a similar pattern.1 Bifidobacterium and Lactobacillus bacteria tend to dominate during the early months of life, and then later in the first year Bacteroides and other adult-like gut bacteria tend to become more common.1–3

Influences on the gut microbiota

A number of things can influence the development of a baby’s gut bacteria population. While scientists are still discovering more about this process, these factors appear to be important:

  • Type of birth – vaginal or Caesarean
  • Gestational age – premature or full term
  • Environmental exposures – eg. parents’ skin-borne bacteria, family pets
  • Diet – breastfed and/or formula fed, types of weaning foods.

As we continue to learn more about the gut microbiota, one thing does seem to be clear: establishing a healthy balance of bacteria early in life is very important to our long-term health.

What are prebiotics, probiotics and synbiotics?

Prebiotics are certain types of carbohydrates that provide food for the ‘good’ bacteria in the gut. Sometimes known as dietary fibre, the scientific definition is ‘…selectively fermented ingredients that result in positive changes in the composition and/or the activity of the gut microbiota, and by doing so, provide health benefits.’4

By helping ‘good’ gut bacteria to thrive, prebiotics can help improve the ratio between ‘good’ and ‘bad’ bacteria. They can also help infants to stay regular and have softer stools.5

Breast milk contains many complex prebiotics, called human milk oligosaccharides (HMOs). Making up around one-third of the composition of breast milk, HMOs have been shown to support the Bifidobacterium and Lactobacillus bacteria that make up the majority of an infant’s gut microbiota. They’ve also been shown to have important health benefits, particularly on the developing immune system.6

Research on HMOs has underlined the importance of prebiotic oligosaccharides in early life nutrition.5

 Probiotics are live, ‘good’ bacteria that help create a healthy gut bacteria profile. Or, in scientific terms, they’re ‘…live microorganisms that, when administered in adequate amounts, provide some health benefit to the person who takes them.’4

Like prebiotics, breast milk also contains an array of probiotics.7 Studies suggest that mothers pass these bacteria onto their babies during breastfeeding.

 Supplementing a baby’s diet with the probiotic called Bifidobacterium lactis Bb12 has been shown to significantly reduce the number of episodes of gastrointestinal infections compared with babies who did not have the probiotic.8

Synbiotics are products that contain both prebiotics and probiotics, creating a synergy between the two (hence the name synbiotic).

An example of a synbiotic food for a baby aged around 8 to 12 months is a little probiotic yoghurt, with a little Freedom Foods Barley+ Muesli softened in milk – yum!


  1. Palmer C et al. Development of the human infant intestinal microbiota. PLoS Biology 2007; 5(7): e177. Accessed via: http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0050177
  2. Obermajer T et al. Microbes in infant gut development: placing abundance within environmental, clinical and growth parameters. Scientific Reports 2017; 7(1): 11230.
  3. Lawley B et al. Differentiation of Bifidobacterium longum subspecies longum and infantis by quantitative PCR using functional gene targets. Peer J 2017; 5: e3375.
  4. World Gastroenterology Organisation Global Guidelines: Probiotics and Prebiotics, October 2011. Accessed via: https://journals.lww.com/jcge/Citation/2012/07000/World_Gastroenterology_Organisation_Global.9.aspx
  5. Skorka A et al. Infant formulae supplemented with prebiotics: are they better than unsupplemented formulae? An updated systematic review. British Journal of Nutrition 2018; 119(7): 810–825.
  6. LoCascio RG et al. Broad conservation of milk utilization genes in Bifidobacterium longum subsp. infantis as revealed by comparative genomic hybridization. Applied and Environmental Microbiology 2010; 76(22): 7373–7381.
  7. Fernandez L et al. The human milk microbiota: origin and potential roles in health and disease. Pharmacological Research 2013; 69(1): 1–10. Accessed via: https://www.sciencedirect.com/science/article/abs/pii/S104366181200165X
  8. Skorka A et al. To add or not to add probiotics to infant formulae? An updated systematic review. Beneficial Microbes 2017; 8(5): 717–725.