What is “the microbiota” versus “the microbiome”? 

The terms “microbiota” and “microbiome” are often used interchangeably, but they mean different things.

The microbiota is all the microorganisms or microbes (bacteria, archaea, fungi, algae, and protists) that live in different parts of your body, like the gut, skin, uterus or breast. Each of us has a unique combination of these microorganisms.

The microbiome is an ecosystem (a biological community) that groups both the microorganisms (the microbiota) and their surroundings together [1].

What is the gut microbiome?

The gut microbiome is all the microbes, and their genes found in your stomach, intestine and colon. It is the largest and most diverse microbiome in all the human body [2].

What does the gut microbiome do? 

Your gut and the microbes that live there help each other out. Your gut provides a nutrient-rich environment for the microbes, and in return, the microbes perform essential functions for your body. Some of these functions include supporting your immunity by strengthening the lining of your stomach and intestine, aiding digestion, or helping produce essential vitamins and hormones [2].

What can affect and change your gut microbiome? 

Many factors can influence your gut microbes, some that you can’t change and others that you can.

The factors you can’t change include age, ethnicity, genetics, hormonal levels and how you were delivered as a baby.

The factors you can change include diet, prebiotics (fibres that feed the microbiota), probiotics (foods that naturally contain microbes, or supplement pills that contain live active microbes), stress, hygiene, alcohol, smoking, antibiotic use, chemotherapy, and radiation [3].

Fig. Factors influencing gut microbiota composition (adapted from [3]).

Can your gut microbiome impact your health?  

Changes in your gut microbiota can influence health, especially if there is an imbalance in the different types of microbes. 

These changes can contribute to a range of illnesses such as irritable bowel syndrome (IBS); obesity; depression; asthma, as well as some cancers. 

Is there a link between the gut microbiome and breast cancer? 

Many studies have looked at the gut microbiome and breast cancer risk, showing that changes or an imbalance in gut microbes is linked to a higher risk of breast cancer. 

How does the gut microbiome influence breast cancer risk? 

There are different ways the gut microbiome can affect breast cancer risk: 

• Oestrogen production – some gut microbes can increase the amount of oestrogen in the body which can increase the risk of breast cancer [4]. 

• Microbial products (substances made by our gut microbes when the body breaks down food, drugs or chemicals) – gut microbes can produce some cancer-protective substances [3]. 

• DNA damage – some gut microbes can damage DNA which can promote breast cancer [3]. 

• Immunity and inflammation – Negative changes to the gut microbiome can lead to long-term inflammation, which can increase the risk of breast cancer [5]. 
• Overweight and obesity – an imbalance in gut microbes can lead to weight gain and obesity, which in turn can increase the risk of breast cancer in post-menopausal women and in men [3,5]. 

Have any other microbiomes been linked to breast cancer? 

Other microbiomes, including the breast, mouth, and skin microbiomes, may have a link to breast cancer risk. However, more research is needed to confirm whether there is a connection between changes in these microbiomes and the risk of breast cancer. 

Further reading

For more information on The Microbiome and Breast Cancer, read our full science review