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What influences an adult’s gut microbiota?

Factors such as diet, exercise and stress can change during adulthood, which in turn can affect the gut microbiota
Microbiota changes during life
© University of Reading

There are factors such as diet, exercise and stress that can change during adulthood, which in turn can affect the gut microbiota.

When bacteria grow they are influenced by a number of factors, these include:

  • How much water is available
  • How acidic the environment is
  • Temperature
  • Oxygen availability
  • How frequently nutrients are replaced
  • What nutrients are available
  • Whether anti-microbial agents are present

During adulthood many of these factors remain fairly stable within our bodies and, as such, the bacteria that grow within us remain quite stable.

Dominating bacteria families

There is a dominance of bacteria within the families Bacteroidetes and Firmicutes. The genus of bifidobacteria, which was such a large component in infancy, is still important but is now typically only 3% of the community.

Evidence shows that whilst the bacterial species present in the gut varies between individuals, the functions that these microorganisms perform are very similar.

Dietary changes

Changes to our diet can however influence the nutrients available to the bacteria and can therefore impact on which bacteria can grow. For example, many species of Clostridium use protein sources for growth, whilst Bacteroides are often well adapted to different carbohydrate sources. Thus, our diet has a great impact on shaping our microbial community.


Additionally medication and antibiotics can prevent the growth of a number of microorganisms in the gut and can therefore lead to changes in the communities within us. This can be seen with the example of antibiotic associated diarrhoea, which is when an antibiotic is taken and causes diarrhoea. This side effect is often due to the fact that many commensal members of our microbial community are restricted and diarrhoea-causing bacteria may get a chance to grow instead.


There are some other factors that can also affect our bacterial communities. For example, it can be seen that people who exercise more have different microbial profiles than those who do not. This could in part be due to differences in protein intake, but differences in gastrointestinal mobility could also be a factor.


Evidence is gathering to support the notion that stress can also impact on our gut microbiota. This has led to much research into how the gut bacteria can impact on the production of neurotransmitters.

To conclude, whilst the gut microbiota of an adult is stable, changes through diet and other external factors can impact on the community within.

© University of Reading
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The Human Microbiome

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