What is the microbiome

The human microbiome is the community of bacteria (microbes) that lives in and on our bodies – on our skin and in our mouths, respiratory tract, gastrointestinal tract and genito-urinary tract.

These bacteria express genes and mean that as humans, we are made up of both human and microbial cells, which define the structure and function of our body. It is so important in fact, that without our microbiome, it is likely that we would not survive beyond five years of age.

The gut microbiome

As part of the overall human microbiome, each of us has around 100,000 billion viable bacteria living in our intestines, comprising over 1,000 different species and more than 5,000 strains. These microbes weigh around 1.5 kg in total and are referred to collectively as the gut microbiome.

95% of the gut microbiome is in the large intestine, with only around 50g (weight) of the microbiome residing in the small intestine.
The gut microbiome is also referred to as the gut bacteria, gut microbes, gut microorganisms, gut microbiota, gut microflora, gut flora and the intestinal bacteria.
Although we all have similar bacteria, everybody has their own individual microbiome, influenced by diet, environment, genetics and early exposure to microbes.

And, just as not all bacteria are bad, our gut bacteria are not all good either. We all carry strains of bacteria that might be considered to be ‘bad’, but balance between the good and the bad microbes is the key to a healthy microbiome. A healthy diet and lifestyle are both key to supporting this balance, as medications (particularly antibiotics), alcohol, sugar and other unhealthy choices will all have an effect and potentially enable the over-growth of the unfriendly microbes.

When does the gut microbiome become established?

The microbiome is established immediately when we are born – at birth, the baby acquires his or her first microbial bacteria from the environment it is born into. For babies born vaginally, the first colonisation is from their mother’s vaginal, skin and rectal bacteria. For those born via caesarean section, these bacteria come from skin and the hospital environment.

A few hours following birth, a mucosal layer starts to form on the baby’s GI tract to act as a barrier to prevent pathogens from crossing into the gut. This mucosal layer is where the beneficial bacteria colonise, helping to reinforce the barrier and support immunity.
The development of the baby’s microbiome is then influenced by diet. Breast milk contains the mother’s bacteria and prebiotic oligosaccharides, which are the fibres that feed the bacteria and help them to colonise as part of the baby’s microbiome.

If the baby is formula fed, he or she will not receive the ‘mammary microbiota’, although many formula milks now contain prebiotic fibre, which helps to feed the existing bacteria in the baby’s microbiome.
When the baby is weaned onto solid foods, the microbiome development will continue based upon the foods that are introduced. can be further supported by Fruits and vegetables help provide prebiotics and plain yoghurt and fermented foods include probiotic bacteria.

Microbiome life stages

Being in the womb is part of the microbiome life stage journey

In utero (womb)

Maternal microbiota
Lifestyle
Diet
Antibiotics

Becoming a newborn is part of the microbiome life stage journey

Birth

Maternal transmission
Vaginal delivery
Caesarean section delivery
Pre-term delivery
Enviroment
Antibiotics

Becoming an infant is part of the microbiome life stage journey

Infancy

Breast feeding
Genetics
Geographical location
Family enviroment
Enviroment
Milk consumption
Solid food intoduction
Antibiotics

Becoming a toddler or child is part of the microbiome life stage journey

Toddler/Child

Full adult diet
Microbiome formed
Lifestyle
Antibiotics

Becoming an adult is part of the microbiome life stage journey

Adult

Full adult diet
Lifestyle
Antibiotics
Aging

Microbiome life stage

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What does the gut microbiome do?

The gut microbiome is made up of specific kinds of micro-organisms that complement each other and their host (person), fulfilling various functions that depend on the species of bacteria. Some bacteria synthesise (produce) vitamins and neurotransmitters, others support digestion and/or absorption of nutrients and some support the immune system.

The bacteria also help to support the function of the mucous membrane (mucosa) that covers the inside surface (wall) of our intestines. The microbes form part of this mucosa as they move through the body and help form a protective barrier to defend against toxins and bad bacteria.

As a result of the many different functions of the gut bacteria, an imbalance of unhealthy and healthy microbes in the intestines has also now been shown to affect health in general.

Can the bacteria in the gut microbiome change over time?

The intestinal microbiome acquires adult characteristics and is fully formed by three years of age. This process is driven by genetic factors and the intake of major food groups by this age.

Whilst the basic structure is established by three years of age however, its total composition will change almost daily throughout our lives. Bacteria forms around half of the faecal mass (poop) we excrete every day and replenishing this bacteria with friendly species depends upon what we eat and drink and any medications and supplements we take on a daily basis.

Before refrigeration was invented, we ate lots of fermented and cultured foods, which gave us an ongoing supply of friendly bacteria and help to maintain balance in the microbiome. Today’s diet lacks these foods and this is where good bacteria supplements have been developed to support our modern diets.

Microbiome fascinating facts

  • Our body contains more microbes (bacteria) than human cells.
  • The bacteria in the human microbiome consists of more than three million genes, compared with the 20-25,000 human genes we all carry.
  • As well as the 100,000 billion microbes in the intestinal microbiome, the skin microbiome hosts 1,000 billion bacteria.
  • Many people assume that the gut bacteria live in the stomach – they actually live in our intestines, as the stomach environment is too acidic for them to survive, and primarily (95%) in our large intestine (colon).
  • Our microbiome is made up of both good and bad bacteria – and that’s fine as long as the right balance is maintained.
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