A man wearing black reading glasses smiles at someone off camera
Trillions of microorganisms live in your gut, mostly bacteria, but also viruses, yeasts, fungi, and parasites.
There are at least as many ‘bugs’ living in you as the number of cells in your body, maybe more. You could say that you’re made up of at least half bug.
Known as your gut microbiome, these microbes play a vital role in how you digest food and absorb nutrients, and influence your metabolism, body weight, immune system, and general health.
But they also influence your brain function. Research reveals that this brain-gut axis (BGA) is a two-way street—there is bi-directional communication between your brain and your gut.
Hormones, neurotransmitters, and immune system factors released by the gut send signals to your brain directly or via autonomic nervous system neurons. This is your gut talking to your brain and nervous system.
Your bug half seems to get a say in matters of both body and mind.
When things go wrong in your gut microbiome, there is evidence that it can affect your mood and may be linked to anxiety and depression.
Where does the gut microbiome come from?
Your orignal gut microbiome is acquired in early childhood. It is passed down at birth from your mother and subsequently from other family members and your environment through your mouth. These microbes you acquire from your environment colonise the digestive tract.
Your mother’s and your close family’s microbiome and the type of birth you had, can affect the microbiome that you develop. Babies born vaginally have other bacteria in their gut compared to babies born by Caesarean section.
What you feed on in the first week after birth also affects your gut levels of bacteria. Studies show a direct correlation between breastfeeding and total numbers (or diversity) of microbial species.
After that, diet, genetics, stress, antibiotics, chemicals, disease, and many other factors determine how your gut microbiome ends up, and how the microbes in the digestive tract shape the immune system.
The first major change is usually when a baby stops breastfeeding and starts eating solid food. Different types of bacteria become dominant and its microbiome changes to a more adult-like state.
Diet plays a key role that continues throughout your life. Changes in diet can alter your gut bacterial makeup in as little as 24 hours.
Most of us have an ‘enterotype’, like a gut fingerprint, with our own unique bacterial signature. In healthy people, most of those bacteria are symbiotic—both we and they benefit from their presence in our gut. A smaller number are pathogenic (disease causing).
The symbiotic and pathogenic bacteria live in balance with no problem. The good bacteria and the immune system prevent the overgrowth of bad ones. But if that balance becomes upset, you can become more prone to disease.
When things go wrong
Changes in diet, stress levels and duration, antibiotics and other factors can change the balance in the microbiome, known as dysbiosis.
The intestine has a special barrier that allows nutrients in but stops food particles and bacteria and their metabolic products from entering the blood stream.
During dysbiosis, this barrier can become more permeable (‘leaky-gut syndrome’) and allow bacteria and molecules into the blood stream that shouldn’t be there.
This impacts the immune system, body and brain, and has been linked to inflammatory bowel disease, diabetes, asthma, anxiety, depression, and other conditions.
How to improve your gut biome
Eat a wide variety of foods
Gut microbiome diversity is higher in people from rural Africa and South America than people from urban areas in Europe and the United States.
This is most likely because their diets are broader than the traditional western diet, and richer in different plant foods.
So, eat a broad range of different foods. Eat more diverse plant foods. Mix it up.
Eat more vegetables, beans, legumes, fruit, and wholegrains
The good bacteria in your gut need to eat too. These foods supply nutrients for a healthy gut microbiome.
They also contain high amounts of fibre and complex carbs, referred to as prebiotics, which can’t be digested by human cells but are loved by beneficial gut bacteria.
The bacteria digest these, producing nutrients and vitamins the body can use. For example, plants and animals do not have the enzymes needed to make vitamin B12 which our bodies need. They are only found in bacteria.
Eat fermented foods
Fermentation is the breakdown of sugars in foods by yeast or bacteria.
Many fermented foods are rich in probiotics—live bacteria and other organisms that provide health benefits when eaten.
Yoghurt is a fermented food that’s excellent for your gut microbiome, containing high levels of a good bacteria called Lactobacillus and nutrients that support the growth of healthy gut bacteria.
Plain yoghurt made from milk and live and active yoghurt bacteria cultures is best, as flavoured yoghurts can contain high amounts of sugar, colourings, and flavourings. Look for ‘live and active cultures’ or similar on the label.
Other good fermented foods are kimchi, sauerkraut, kombucha, tempeh, kefir, miso, natto, and sourdough.
Eat polyphenol- and antioxidant-rich foods
Polyphenols are compounds found in plant foods that have many health benefits. They can have an anti-inflammatory effect, are powerful antioxidants that can neutralise harmful free radicals, and they may help promote the growth of beneficial gut bacteria.
They occur naturally in many foods, but you can find them in higher quantities in:
- dark chocolate
- tea (black and green)
- cocoa
- coffee
- blueberries, blackberries, and many other berries
- grapes, apples, cherries
- olives
- almonds, chestnuts, hazelnuts, flax seeds, pecans, and walnuts
- broccoli, carrots, and asparagus
- caraway, cinnamon, cloves, cumin, and curry powder
- basil, marjoram, parsley, peppermint, rosemary, sage, and thyme.
Take probiotic supplements
Probiotic supplements have beneficial bacteria and yeasts to help restore the balance in the gut microbiome. They are thought to have little effect on the gut microbiome in healthy people but may benefit people who have been on antibiotics or whose gut microbiomes have been impacted by medication, special diets, disease, or other factors.
Faecal transplants
In people with certain infections, such as Clostridium difficile (C. diff), a bacterial infection which causes severe diarrhoea, nausea, fever and stomach pain that can progress and become fatal if left untreated, or those with chronic overgrowth or imbalances in their microbiome, faecal transplants can be administered to control infections and restore the gut microbiome.
A faecal transplant is a procedure in which healthy stool from a screened donor is processed into a product suitable for transplantation. A gastroenterologist then introduces the product into the patient's gut. A fecal transplant is also known as a faecal microbial transplantation (FMT).
Clinical studies show that FMT has an 80-90% success rate in treating patients with C. diff. It can relieve symptoms, including inflammation of the colon, within a week.
More information
- Decades-old assumption about microbiota revisited | Nature
- Gut microbiota’s effect on mental health: The gut-brain axis | National Library of Medicine
- How to improve your gut biome | Healthline
- The microbiome | Harvard T.H. Chan School of Public Health
- What is the gut microbiome? | Deakin University Food and Mood Centre
- How super poo will help wipe out a patient's dangerous bacteria | Cairns and Hinterland Hospital and Health Service