Your gut is about much more than digestion.
The microorganisms living in your digestive system — collectively known as your gut microbiome — interact with your immune system, metabolism, intestinal lining and nervous system. Researchers are also investigating how the gut microbiome communicates with other parts of the body through what are known as the gut–organ axes. These include the gut–brain, gut–liver, gut–kidney and gut–heart axes. (pubmed.ncbi.nlm.nih.gov)
You may have heard that “70–80% of your immune system is in your gut”.
There is a good reason this idea has become popular: a substantial amount of immune tissue is associated with the gastrointestinal tract, and your gut microbiota has an important role in educating and regulating immune responses. However, putting a precise percentage on how much of your immunity “depends on your gut” oversimplifies a very complex system. (pubmed.ncbi.nlm.nih.gov)
What we do know is that your gut microbiome is an important part of your overall health.
And one of the most practical ways to support it is through the food you eat.
Your Gut Microbiome Is More Than Just “Good” and “Bad” Bacteria
One of the most common messages online is that you need to increase your “good bacteria” and get rid of your “bad bacteria”.
Real microbiome science is much more complicated.
Your gut contains a huge community of microorganisms, and different species and strains can play different roles depending on the environment they live in.
A healthy microbiome isn’t simply about having lots of one particular bacterium.
Researchers are increasingly interested in:
- Microbial diversity
- Microbial function
- The metabolites microorganisms produce
- The relationship between microorganisms and the intestinal lining
- How the microbiome interacts with the immune system
This is why variety is more useful than trying to maximise one particular bacterium.
There is no single “perfect” microbiome that every person needs.
Do You Need Lots of Probiotics?
Not necessarily.
A probiotic is a live microorganism that, when consumed in an adequate amount, provides a health benefit.
Importantly, probiotics are strain-specific.
This means taking a large amount of one probiotic does not automatically create a more diverse gut microbiome, and a probiotic supplement isn’t a replacement for dietary variety.
In fact, studies investigating probiotic supplementation during antibiotic treatment have not consistently shown that probiotics restore overall gut microbial diversity. (pubmed.ncbi.nlm.nih.gov)
So rather than thinking:
“I need more probiotics.”
Think:
“How can I support the whole ecosystem in my gut?”
What About Fermented Foods?
Fermented foods can be a delicious way to add variety to your diet.
Some fermented foods contain live microorganisms, including:
- Yoghurt containing live cultures
- Kefir
- Kimchi
- Sauerkraut
- Tempeh
- Natto
However, fermented foods are not automatically probiotic foods.
The microorganisms present vary according to the food, production method and storage conditions. A fermented food also doesn’t necessarily contain a specific microorganism that has been clinically shown to provide a health benefit.
So choose fermented foods because you enjoy them and they fit into your diet — not because you believe you need to consume a certain number every day. (pubmed.ncbi.nlm.nih.gov)
The Biggest Food Priority: Feed Your Gut Microorganisms
Once you’ve considered fermented foods, the next question is:
What feeds the microorganisms already living in your gut?
One of the most important answers is dietary fibre.
Fibre reaches parts of the digestive tract without being completely digested and can provide substrates that gut microorganisms use.
Different types of fibre have different characteristics, and foods often contain more than one type.
Three commonly discussed types are soluble fibre, insoluble fibre and resistant starch.
Soluble Fibre
Soluble fibre can dissolve or swell in water and some types form a gel-like substance.
It is found in foods such as:
- Oats
- Barley
- Legumes
- Fruit
- Some vegetables
Some soluble fibres can be fermented by gut microorganisms.
Soluble fibre can also help support healthy blood cholesterol levels and, depending on the food and type of fibre, may slow digestion and influence blood glucose responses.
For example, oats and barley contain beta-glucan, a type of soluble fibre with well-established cholesterol-lowering effects when eaten in sufficient amounts.
Insoluble Fibre
Insoluble fibre doesn’t dissolve in water and contributes to stool bulk.
It is found in foods such as:
- Wholegrain breads and cereals
- Wheat bran
- Nuts
- Seeds
- Vegetable skins
- Fruit skins
Insoluble fibre can help support regular bowel movements and normal digestive function.
It’s important not to think of insoluble fibre as a substance that simply “scrubs toxins out of your gut”.
Instead, its main benefit is helping maintain healthy stool consistency and bowel transit.
Resistant Starch
Resistant starch is a type of starch that resists digestion in the small intestine and can reach the large intestine, where gut microorganisms can ferment it.
Sources include:
- Legumes
- Green or underripe bananas
- Oats
- Barley
- Cooked and cooled potatoes
- Cooked and cooled rice
- Cooked and cooled pasta
When resistant starch is fermented, it can contribute to the production of short-chain fatty acids such as butyrate.
Butyrate is an important energy source for cells lining the colon and is one reason resistant starch and other fermentable fibres are being investigated for their effects on gut health. (pubmed.ncbi.nlm.nih.gov)
So resistant starch is certainly an important type of carbohydrate for your gut microorganisms — but it isn’t the only “gold star” fibre.
Your gut benefits from a mixture of different fibres.
Variety Is the Secret Ingredient
Different plant foods provide different combinations of fibre, resistant starch and other compounds.
This is why dietary diversity matters.
Try including:
Wholegrains
- Oats
- Wholegrain bread
- Brown rice
- Quinoa
- Barley
- Wholegrain pasta
Fruit
- Berries
- Apples
- Bananas
- Kiwi fruit
- Oranges
- Stone fruit
Vegetables
Include a mixture of colours and types.
Legumes
- Chickpeas
- Lentils
- Kidney beans
- Black beans
- Peas
Nuts and Seeds
- Almonds
- Walnuts
- Chia seeds
- Pumpkin seeds
- Flaxseeds
Even small amounts count towards variety.
You don’t need to eat exactly 30 different plant foods every week, but using 30 as a fun goal can be a useful way to encourage variety if it suits you.
Don’t Forget Polyphenols
Fibre isn’t the only way plant foods interact with your microbiome.
Plants also contain polyphenols, a large family of naturally occurring compounds found in foods and drinks such as:
- Berries and other fruit
- Vegetables
- Wholegrains
- Nuts
- Seeds
- Tea
- Cocoa
- Herbs and spices
- Extra virgin olive oil
Some polyphenols are absorbed in the small intestine, while a significant proportion reaches the colon, where gut microorganisms can transform them into other compounds.
This creates an interesting two-way relationship:
Your diet influences your gut microorganisms, and your gut microorganisms influence how your body processes some of the compounds in your diet. (pubmed.ncbi.nlm.nih.gov)
This is another reason why a varied plant-rich diet provides much more than fibre alone.
What About Antibiotics?
Antibiotics are incredibly important medicines when they are needed.
They can also affect the gut microbiome because they don’t only target the bacteria causing an infection; they can alter other bacteria in the gut as well.
Studies show that antibiotics can cause relatively rapid changes in gut microbial composition and diversity. In many people, the microbiome moves back towards its previous state after treatment, although some changes can persist for longer. (pubmed.ncbi.nlm.nih.gov)
This doesn’t mean that you should avoid antibiotics.
Quite the opposite.
Take antibiotics when they are appropriately prescribed, and don’t use them when they aren’t needed.
Antibiotic stewardship protects both your health and the wider community by reducing unnecessary antibiotic exposure and resistance.
Stress and Your Gut
Your gut and brain communicate in both directions.
Stress can influence digestion, bowel habits, gut barrier function and the gut microbiome. At the same time, the gut microbiome can influence signalling pathways involved in stress and the nervous system.
Research in humans has found associations between psychological stress and changes in the abundance of some gut microorganisms, although the relationship is complex and varies between people. (pubmed.ncbi.nlm.nih.gov)
This is another reason why gut health isn’t purely about what you eat.
Stress management matters too.
Sleep Matters Too
Sleep and your gut microbiome also appear to influence each other.
A recent systematic review of 41 human studies found that sleep restriction, sleep disturbances and circadian disruption may be associated with changes in gut microbiome composition and function, although findings were mixed. (pubmed.ncbi.nlm.nih.gov)
So supporting your gut isn’t just about adding another food to your shopping list.
Getting enough sleep and maintaining a reasonably consistent routine are also part of looking after your whole body.
How Does Your Gut Connect With the Rest of Your Body?
The microbiome doesn’t operate in isolation.
Gut microorganisms and their metabolites can communicate with other parts of the body through several pathways.
Research is investigating relationships between the gut microbiome and:
The Brain
The gut–brain axis involves the nervous system, immune pathways, hormones and microbial metabolites.
The Liver
The gut and liver are closely connected through blood flow and bile-acid metabolism, forming the gut–liver axis.
The Kidneys
Gut-derived metabolites and changes in microbial function are being investigated in relation to kidney health.
Metabolism and Blood Glucose
Gut microorganisms can influence the production of metabolites involved in energy metabolism and insulin sensitivity.
Cardiovascular Health
Research is investigating how microbial metabolites, bile acids, inflammation and other pathways may influence cardiovascular health.
These are fascinating areas of research, but the gut microbiome is one contributor among many. Your diet, physical activity, genetics, sleep, medications and other health factors all matter. (pubmed.ncbi.nlm.nih.gov)
Build Your Gut Garden
A helpful way to think about your gut microbiome is as an ecosystem.
Rather than trying to plant one species of flower and make it grow as much as possible, you want to create an environment where a range of microorganisms can thrive.
You can do this by:
Feeding your gut with different plant fibres.
Including a variety of whole plant foods.
Adding fermented foods you enjoy.
Including polyphenol-rich foods.
Taking antibiotics only when medically appropriate.
Looking after your sleep and stress levels.
And perhaps most importantly, don’t make gut health unnecessarily complicated.
You don’t need a cabinet full of supplements or a strict list of “good” and “bad” foods.
What Could a Gut-Friendly Day Look Like?
Breakfast
- Rolled oats
- Milk or yoghurt
- Banana
- Berries
- Chia seeds
Lunch
- Wholegrain wrap
- Chickpeas or chicken
- Spinach
- Tomato
- Avocado
- Hummus
Snack
- Yoghurt containing live cultures
- Apple
- Handful of walnuts
Dinner
- Salmon or tofu
- Cooked and cooled/reheated brown rice
- Broccoli
- Carrots
- Lentils
- Extra virgin olive oil
Add flavour
- Garlic
- Ginger
- Turmeric
- Herbs
- Spices
This type of eating pattern provides a broad range of fibres, resistant starches, plant compounds, protein, healthy fats, vitamins and minerals.
How Much Fibre Do You Need?
For Australian adults, the recommended adequate intake is:
- Women: 25 g of fibre per day
- Men: 30 g of fibre per day (eatforhealth.gov.au)
Many people don’t meet these recommendations.
Rather than trying to dramatically increase your fibre intake overnight, gradually add more plant foods to your meals.
For example, add:
- Fruit to breakfast
- Legumes to dinner
- Vegetables to lunch
- Seeds to yoghurt
- Wholegrain bread instead of refined bread
If you currently eat very little fibre, increase it gradually and make sure you drink enough fluid.
Take Home Message
Your gut microbiome is a fascinating part of your overall health.
It interacts with your intestinal lining, immune system, metabolism and nervous system, while research is continuing to uncover connections between the gut and organs throughout the body.
You don’t need to create a “perfect” microbiome.
Instead, create an environment where a diverse community of microorganisms can thrive.
Make plant foods your friend.
Eat a variety of wholegrains, vegetables, fruit, legumes, nuts and seeds. Include different types of fibre and enjoy fermented foods that you like. Add herbs, spices and other polyphenol-rich foods for even more variety.
Look after your sleep, manage stress and only use antibiotics when they are medically appropriate.
Think of your gut like a garden: the goal isn’t to grow one type of plant as much as possible. It’s to create a healthy environment where a diverse ecosystem can flourish.
How Feed Your Future Dietetics Can Help
Gut-health information can become overwhelming when social media is full of advice about probiotics, microbiome testing, supplements and restrictive diets.
At Feed Your Future Dietetics, I help you separate evidence-based nutrition from the latest gut-health trend and turn the science into practical strategies that fit your lifestyle.
Whether you’re looking to improve your gut health, increase your fibre and plant-food intake, manage gastrointestinal symptoms or simply create a more balanced eating pattern, nutrition can be tailored to your individual needs without unnecessary restriction.
With over 10 years of experience supporting Australians with their nutrition and health goals, Feed Your Future Dietetics provides individualised dietetic support Australia-wide via Telehealth using Zoom or Microsoft Teams.
To learn more or book an appointment:
ashleigh@feedyourfuturedietetics.com
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- Gut-associated lymphoid tissue: a microbiota-driven hub of B cell immunity. Trends in Immunology. 2024.
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- Dietary fibre. Australian Government, Eat For Health: Nutrient Reference Values.
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- Antibiotic-induced changes in the human gut microbiota for the most commonly prescribed antibiotics in primary care: a systematic review. 2020.
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