Gut health has become a popular topic over the past decade, with good cause – the microbes living in your gut play an incredibly important role in keeping you healthy. Despite this being a fairly new area of research, we’re learning a lot about what our gut microbiota (GM) does for us.
What is the gut microbiota?
You might also see the term ‘gut microbiome’ often being used in reference to gut health: the terms microbiota and microbiome are often used interchangeably, but have slightly different meanings. The microbiota refers to the community of microbes that live on and in different areas of your body (including the skin, mouth and gut), while the microbiome includes the microbiota as well as its genetic material. The gut is where the majority of your microbes live, and around 90-95% of your entire microbiota reside in your gut. Your GM contains around 100 trillion bacteria, virus, fungi and other microbes, and weighs roughly the same as your brain.
Your microbiota is unique, like a fingerprint
Although your GM is unique to you and is initially influenced by genetics, it is also dynamic. Factors such as physical and emotional environment, exercise, diet, stress, sleep, illness and antibiotic use can influence what types of microbes and how many of these you have in your GM.
Diet and lifestyle factors during pregnancy can modify the mother’s GM which is then transferred to baby, in the case of a vaginal delivery – this is currently believed to be how our GM is initially established. For babies born by caesarean section, baby's GM usually contains microbes normally found on skin and in the hospital environment.
After birth our GM is influenced by whether we receive formula or breastmilk, and by the types of foods we eat once we start solid foods. During the first 2 years of life the GM is very dynamic and diverse, but can also be impacted by illness and antibiotic use. Once we’re about 3 years old the GM tends to resemble that of an adult.
During adulthood your GM is relatively stable, but can still be modified by diet and lifestyle factors. As you age diversity decreases, and the amount of potentially harmful microbes may increase - this could be due to lifestyle changes (we often become less active with age), diet (consuming a less diverse diet), as well as increased medication use.
Not all bacteria are bad
Both beneficial and pathogenic (illness-causing) microbes live in your GM in a delicate balance – an imbalance in favour of pathogenic types can increase risk of health problems. Your GM is involved in many important functions, and communicates with other organ systems including your nervous system, brain and liver.
Gut bacteria are also responsible for fermenting undigested food particles such as fibre, and produce some B vitamins, vitamin K, amino acids (building blocks of proteins), and neurotransmitters. They also produce short chained fatty acids (SCFAs), which play a role in regulating appetite, as well as reducing pain and inflammation. The gut also plays an essential role in immune function: at least 70% of your immune system is in your gut, and gut bacteria produce anti-inflammatory and antimicrobial compounds, and compete with pathogens for receptor sites on cells.
An imbalance in microbiota may impact health
Imbalances in GM have been associated with a number of health conditions including Irritable Bowel Syndrome (IBS), Inflammatory Bowel Disease (IBD), allergies, asthma and eczema. Some studies have also found links with bowel cancer, autism, dementia and Parkinson’s Disease. GM disturbances have also been associated with metabolism, immune function, diabetes, obesity and mental illness.
Gut microbiota and mental health
The gut and brain communicate via what is known as the gut-microbiota-brain axis, and gut bacteria produce neurotransmitters (eg. dopamine and serotonin) which participate in this process. GM disturbances have been associated with mental illness including depression and anxiety, and this appears to be a two-way relationship: stress and mental illness can also impact the GM (in part by influencing our food choices) and worsen gut symptoms – this is often seen in people with gut conditions such as IBS. Recent research has found that diet (especially a Mediterranean dietary pattern) can alter the GM and improve symptoms of mental illness.
Your gut microbiota may influence your weight
Gut bacteria produce SCFAs which regulate appetite and metabolic functions, and these can influence insulin response and weight. An association has been found between an imbalance in GM and obesity, and research has shown positive effects on both GM and weight through dietary interventions, as well as transplant of faecal microbiota from a healthy donor (faecal microbiota transplant).
Looking after your microbiota
Although it's not possible to change some of the factors that influence your GM, there are still many areas where you can have a positive impact on your GM, particularly through diet and lifestyle changes. We still don’t know enough yet to say exactly what an optimal GM looks like (it’s likely this is also very individual anyway), but we do know that diversity and abundance are important.
Diversity: your GM reflects your diet, and a GM with many different beneficial bacteria types (diversity) tends to be more resilient to pathogens.
Abundance: it’s ideal to have as many as possible of the beneficial types of bacteria. These tend to be bacteria that thrive on digesting fibre from plants.
The typical “Western” diet tends to be high in ultra-processed foods which reduces diversity and abundance of bacteria, while a diet based upon minimally-processed foods and rich in plant foods promotes increased diversity and abundance of beneficial bacteria types.
How can you increase diversity and abundance?
Include as many different types of plant foods as possible in your diet. Research has found that people who ate at least 30 different types of plant foods per week had a more diverse GM.
Include prebiotic foods in your diet. Prebiotics are types of fibre that can be fermented by your gut bacteria. Only certain types of fibre have prebiotic properties, so not all fibre is prebiotic. Resistent starch, which forms when starchy foods are cooked and cooled (eg. potato, pasta, rice) also has prebiotic properties. Prebiotic foods include garlic, onion, asparagus, and legumes.
Include enough fibre in your diet. Fibre helps with normal gut function and promotes regular bowel movements. Recommended daily intakes* for fibre are: 25-35g/d for adults 10.6-15.9g/d for children 2-5 years 13.8-20.7g/d for children 6-9 years
Include regular physical activity. Physical activity can also increase GM diversity and abundance, increase production of the beneficial compounds your gut bacteria produce, and can help improve bowel function. Aim for: At least 60 min physical activity per day for children At least 150 min moderate-intensity or 75 min high-intensity activity per week for adults.
Get enough sleep. Sleep quality can impact GM diversity and abundance, and your GM may also impact your sleep quality - so it's important to focus on both aspects for optimal overall health. Poor sleep can contribute to your body's stress response, which can negatively impact your GM. Lack of sleep can also impact food choices, also impacting your GM. You can read more about sleep and health here.
*Based upon current European recommendations