How gut health supports your immune system

Discover how your gut microbiome shapes immunity. Learn everyday habits, foods and supplements to support gut and immune health, the Blackmores way.

Inside your digestive tract lives a community of trillions of microorganisms that influence far more than just digestion. The gut microbiome plays an active role in how the immune system develops, signals and responds, and the science describing this relationship has expanded considerably over the past decade. Around 70% of the body's immune cells are housed in tissue lining the gut, making it one of the most active immune sites in the human body.

This article looks at what the gut microbiome is, how it interacts with the immune system, and the everyday habits that help maintain a balanced, well-functioning gut.

What is the gut microbiome?

The gut microbiome refers to the trillions of bacteria, viruses, fungi and other microorganisms that live in your digestive tract, mostly in the large intestine. A review published in Nutrients describes the gut as the largest and most diverse microbial community in the human body, with each person carrying a microbial profile shaped by genetics, mode of birth, early nutrition, diet, environment and antibiotic exposure.

Composition varies from person to person, though a healthy microbiome typically shows wide diversity, with many beneficial species working alongside one another. This community contributes to digestion, vitamin production (such as vitamin K and several B vitamins), nutrient absorption and immune function.

How are gut health and the immune system connected?

The gut–immune axis describes the constant, two way communication between your gut microbiome and your immune system. The microbiome shapes how immune cells develop and respond, and the immune system in turn helps regulate which microbes thrive in the gut.

The Nutrients review also outlines that approximately 70% of the body’s immune cells reside in gut associated lymphoid tissue (GALT). This tissue acts as a barrier between the contents of the gut and the rest of the body, training immune cells to tell the difference between harmful invaders and beneficial microbes.

From early infancy, the developing microbiome plays a role in how immune cells learn to respond. That early "education" continues throughout life, with the microbial community influencing inflammatory signalling, antibody production and the activity of various immune cell types.

The role of beneficial bacteria in immune function

Beneficial bacteria contribute to immune function through several connected mechanisms.

Producing short chain fatty acids (SCFAs): When gut bacteria ferment dietary fibre, they produce short chain fatty acids such as butyrate, propionate and acetate. A 2024 review in Nature Reviews Immunology describes how SCFAs help regulate the gut barrier, mucosal immunity and the activity of immune cells across the body.

Maintaining the gut barrier: A balanced microbiome supports the cells that line the intestine, which form a physical barrier preventing unwanted substances from entering the bloodstream.

Crowding out unwanted microbes: Beneficial bacteria compete with potentially harmful ones for nutrients and attachment sites along the gut wall, which helps preserve microbial balance.

Communicating with immune cells: Bacterial metabolites influence the development and behaviour of regulatory immune cells, contributing to how the body manages inflammation day to day.

What can disrupt gut microbiome balance?

A range of everyday factors can shift the balance of the gut microbiome, sometimes called dysbiosis. Common contributors include:

• A diet low in fibre and high in ultra processed foods
• Frequent or repeated courses of antibiotics
• Ongoing stress
• Poor sleep quality
• Excessive alcohol consumption
• Limited physical activity

The Nature Reviews Immunology review notes that prolonged disruption to the microbiome can affect SCFA production and immune signalling. Many of these factors are within everyday control, and small, repeated changes can support a more balanced microbial community.

Signs your gut microbiome may benefit from extra support

Your gut often signals when it’s out of balance. Some common signs that your microbiome may benefit from a closer look at diet and lifestyle include:

• Irregular bowel habits, such as occasional bloating or changes in stool consistency
• Feeling sluggish after meals
• Unexplained skin changes
• Difficulty digesting certain foods
• Lower energy through the day

These signs are not diagnostic. Persistent or worsening symptoms should be discussed with a healthcare professional, as they may point to something that needs proper assessment.

Everyday habits that support gut and immune health

Building a balanced microbiome is a daily practice. Small, repeated choices over weeks and months shape the diversity of your gut bacteria.

Eat a wide variety of plant foods

Diversity in the diet supports diversity in the gut. Vegetables, fruits, legumes, nuts, seeds and whole grains each feed different beneficial microbes. The American Gut Project found that people who consumed more than 30 different plant foods per week had more diverse gut microbiomes than those eating fewer than 10.

Get enough fibre

Fibre is the primary fuel for beneficial gut bacteria. Despite this, most Australians fall short of recommended intakes. An analysis of National Nutrition and Physical Activity Survey data found that more than 7 in 10 Australian adults did not meet the Adequate Intake (AI) for fibre, which Health Direct sets at 25g per day for women and 30g per day for men.

Good sources include oats, legumes, whole grain bread, fruit eaten with the skin on, and a wide mix of vegetables.

Include fermented foods

Fermented foods such as yoghurt, kefir, kimchi, sauerkraut and miso introduce live microbes and microbial metabolites to the gut. A 2021 study in Cell found that a diet rich in fermented foods over 10 weeks increased gut microbial diversity in healthy adults and was associated with reduced markers of inflammation.

Prioritise sleep and manage stress

The gut and brain communicate through the gut–brain axis. Disrupted sleep and ongoing stress can shift microbial balance, while consistent rest and stress regulation contribute to a steadier microbial environment.

Stay active

Regular movement is associated with greater microbial diversity. Even moderate activity, such as daily walks, has been linked to favourable shifts in gut bacteria composition.

Probiotics, prebiotics and postbiotics explained

These three terms often appear together but describe different things.

Probiotics

Probiotics are live beneficial bacteria, typically delivered through fermented foods or supplements. Common strains include species of Lactobacillus and Bifidobacterium. You can read more about this in the Blackmores guide to probiotics and gut health.

Prebiotics

Prebiotics are fibres that resist digestion in the small intestine and feed beneficial gut bacteria in the colon. Foods rich in prebiotics include garlic, onions, leeks, asparagus, slightly underripe bananas, oats and legumes. Inulin and fructo-oligosaccharides (FOS) are two well studied prebiotic fibres.

Postbiotics

Postbiotics are the beneficial compounds produced during probiotic fermentation, along with non viable microbial cells and their components. Because they do not rely on live bacteria surviving the journey through the digestive tract, postbiotics offer a stable approach to formulating gut and immune supplements.

Blackmores Gut Immune Biotic is one example of a postbiotic formulation. Each daily dose (two tablets) contains 250mg of Wellmune®, a clinically trialled Saccharomyces cerevisiae (yeast) cell wall extract, alongside 1000mg of vitamin C and 14mg of zinc. Vitamin C and zinc are nutrients that support healthy immune system function and contribute to general health and wellbeing. The formula is shelf stable, taken with food, and is for adults only.

For those looking for a higher dose vitamin C option to sit alongside their daily routine, Blackmores Bio C 1000 provides 1000mg of vitamin C per tablet, plus citrus bioflavonoids, hesperidin, acerola (Malpighia glabra) and rosehip (Rosa canina). Vitamin C supports healthy immune system function, acts as an antioxidant that helps reduce free radical damage to body cells, and contributes to collagen formation. Vitamin and mineral supplements should not replace a balanced diet.

Building a simple daily gut health routine

A practical daily routine doesn't need to be complicated:

• Aim for a varied breakfast that includes fibre, such as oats with fruit and nuts
• Add at least one serve of vegetables to lunch and dinner
• Include a fermented food a few times a week
• Drink plenty of water across the day
• Get outside for some movement, even a short walk
• Wind down before bed to support sleep quality

If you choose to add a supplement, take it consistently and with food where the label suggests. Consistency over weeks tends to matter more than perfection in any single day.

When to see a healthcare professional

Many gut health concerns respond well to dietary and lifestyle changes. Some warrant professional input. Talk to your GP, dietitian or naturopath if you experience persistent digestive changes lasting more than a few weeks, unexplained weight changes, ongoing fatigue, blood in stools, or if you have a medical condition that affects digestion. A healthcare professional can help identify underlying causes and tailor an approach that fits your circumstances.

Key takeaways

The gut and immune system are closely linked, with around 70% of immune cells located in gut tissue. The microbiome influences immune training, inflammatory signalling and barrier function. A diverse, balanced microbiome is supported by a varied diet rich in fibre and plant foods, regular movement, restful sleep and stress regulation.

Probiotics, prebiotics and postbiotics each offer distinct ways to support gut balance. A quality supplement can sit alongside everyday choices rather than replace them. Maintaining gut health is a daily practice, built from small, consistent steps.

Frequently asked questions

How is gut health linked to immunity?

The gut hosts approximately 70% of the body's immune cells in gut associated lymphoid tissue. According to a review by Nutrients the microbiome interacts with these cells to support immune training, regulate inflammation and influence how the immune system responds.

What is the gut microbiome?

The gut microbiome is the community of trillions of bacteria, viruses, fungi and other microbes living in the digestive tract. It contributes to digestion, vitamin production, nutrient absorption and immune function.

Can poor gut health affect immunity?

Disruption to the microbiome, often called dysbiosis, can affect immune signalling and gut barrier function. Maintaining a balanced microbiome through diet and lifestyle supports normal immune function over time.

Can probiotics or postbiotics support immune health?

Probiotics, prebiotics and postbiotics may contribute to a balanced gut microbiome. Some clinically studied ingredients, such as the postbiotic Wellmune®, alongside nutrients like vitamin C and zinc, support healthy immune system function as part of a balanced diet and lifestyle.

How long does it take to support gut health?

Gut microbiome shifts can begin within days of dietary changes, but meaningful, lasting differences typically take several weeks to months of consistent habits.

Always read the label and follow the directions for use.

Disclaimer: This article provides general information only and is not intended to diagnose, treat, cure, or prevent any disease. The information presented is not a substitute for professional medical advice. If you have concerns about your health, please consult your GP or healthcare provider for personalised assessment and recommendations. Supplements should not replace a balanced diet.