Best foods for gut and immune health

Discover how fibre, fermented foods and key nutrients support gut health and immune function. Practical, everyday food tips for Australian adults.

The food on your plate has a closer relationship with the immune system than many people realise. A review by Tissue Barriers notes that the gastrointestinal tract can harbour up to 70% of the body's lymphocytes, which makes everyday food choices one of the most direct ways to support both digestive and immune health. Despite this, data published in Nutrients from the most recent National Nutrition and Physical Activity Survey shows that more than 7 in 10 Australian adults fall below the adequate intake for fibre, and over 4 in 5 don't meet the Suggested Dietary Target.

This article looks at the foods, nutrients and patterns of eating that research links most strongly to a balanced gut microbiome and supportive immune function. The focus is practical: ingredients you can find at any Australian supermarket, integrated in a way that fits real life.

Why diet plays a central role in gut and immune health

The gut-associated lymphoid tissue, often shortened to GALT, is the largest immunological organ in the body. The GALT contains a substantial proportion of the body's immune cells, including dendritic cells, lymphocytes and Peyer's patches. This is where immune cells encounter food particles and microbes, shaping how the immune system responds throughout the body.

The trillions of microbes living in the gut, collectively known as the gut microbiota, sit at the centre of this interaction. A 2025 review in Frontiers in Microbiology described how a balanced gut microbiome contributes to effective immune defences, while reduced microbial diversity has been linked to less effective immune responses.

Diet is the most consistent factor that shapes the gut microbiome day to day. The microbes you feed determine which species thrive, and the byproducts of microbial fermentation, such as short-chain fatty acids, play roles in immune regulation. A 2025 review in the International Journal of Molecular Sciences reported that high fibre dietary patterns are linked with reduced inflammatory markers in both observational and intervention studies.

Key nutrients that support the microbiome

Several nutrients have documented roles in supporting gut microbial balance, immune function or both.

Fibre: The foundation nutrient for gut health. Different types of fibre feed different microbes, and a varied intake supports microbial diversity. A 2025 meta-analysis in The Journal of Nutrition found that fibre interventions were associated with a significant reduction in C-reactive protein, a marker of inflammation, across 25 randomised controlled trials.

Polyphenols: Plant compounds found in colourful fruits, vegetables, olive oil, tea and dark chocolate. A 2025 review in Nutrients on Mediterranean diet patterns highlighted polyphenols from extra virgin olive oil as foods that may help foster the growth of beneficial bacteria including Faecalibacterium prausnitzii and Roseburia.

Vitamins C and D and zinc: Three of the most studied micronutrients for immune function. Vitamin C contributes to the normal function of the immune system. Vitamin D plays a role in modulating both innate and adaptive immune responses. Zinc is involved in the development and activity of immune cells. A review in IDOSR Journal of Science and Technology summarised the supporting roles of these micronutrients in immune cell production and inflammation regulation.

Omega-3 fatty acids: Found in oily fish, walnuts and flaxseeds, omega-3 fatty acids contribute to the regulation of inflammatory processes that interact with immune function.

Selenium and iron: Both are involved in normal immune function. Selenium is found in Brazil nuts and seafood, while iron sources include lean red meat, legumes and dark leafy greens.

Prebiotic foods and fibre explained

Prebiotics are types of dietary fibre that pass undigested through the small intestine and reach the colon, where they're fermented by gut bacteria. This fermentation produces short-chain fatty acids that contribute to gut barrier integrity and help shape immune responses.

Not all fibre is prebiotic, but many fibre rich plant foods contain prebiotic compounds such as inulin, fructooligosaccharides (FOS) and galactooligosaccharides (GOS).

Prebiotic rich foods to include

Common prebiotic-containing foods include:

• Onions, garlic and leeks
• Asparagus
• Jerusalem artichokes
• Bananas (especially slightly green)
• Oats and barley
• Legumes such as lentils, chickpeas and kidney beans
• Apples (with the skin)
• Wholegrain wheat products

The Australian Dietary Guidelines recommend an Adequate Intake of 25g of fibre per day for women and 30g for men, with Suggested Dietary Targets of 28g and 38g respectively to reduce chronic disease risk. However, the 2018 Nutrients analysis of the National Nutrition and Physical Activity Survey found that more than 4 in 5 Australian adults don't meet the higher target, leaving room for everyday improvements through varied wholefoods.

Everyday foods that support immune function

Different foods contribute different nutrients to immune function. Variety matters more than perfection.

Vitamin C rich foods

Vitamin C contributes to the normal function of the immune system and supports antioxidant defences. Australian sources of vitamin C include capsicum (red capsicum is particularly rich), strawberries, kiwi fruit, citrus, broccoli, Brussels sprouts and tomatoes. Because vitamin C is water soluble and not stored in the body, regular daily intake is helpful.

Foods for vitamin D, zinc and selenium

Vitamin D: Oily fish (salmon, sardines, mackerel), egg yolks and some mushrooms exposed to UV light. Australia's main source for most people is sunlight, with diet contributing a smaller share of daily needs.

Zinc: Lean red meat, oysters, pumpkin seeds, chickpeas, cashews and wholegrains.

Selenium: Brazil nuts (just one or two daily can meet selenium needs), tuna, sardines, eggs and wholegrain bread.

Fermented foods

Fermented foods contain live microbes or microbial byproducts that may contribute to gut microbial diversity. A study from the Stanford School of Medicine found that adults who consumed about six servings of fermented foods per day for 10 weeks had a measurable increase in gut microbiome diversity and a decrease in 19 inflammatory markers, including interleukin-6.

Common fermented foods include:

• Yoghurt and kefir (look for "live cultures" on the label)
• Sauerkraut and kimchi (refrigerated, unpasteurised)
• Kombucha
• Miso and tempeh
• Some aged cheeses

Colourful plants and herbs

Berries, leafy greens, tomatoes, beetroot, ginger and turmeric add polyphenols and other plant compounds that have been linked to gut microbial diversity and immune function.

Building a gut friendly eating pattern

No one ingredient will make or break gut health. The patterns that emerge across days and weeks matter more.

A few principles supported by current research:

Eat a wide range of plants: Microbiome research has consistently linked plant variety with greater microbial diversity. Vegetables, fruits, nuts, seeds, legumes, herbs and spices all count.

Combine fibre and fermented foods: The Stanford trial suggested that fermented foods may have a particularly noticeable effect on microbial diversity and inflammatory markers, while fibre supports the production of short-chain fatty acids in the colon.

Lean toward a Mediterranean-style pattern: A review in BMC Medical Genomics found that adherence to the Mediterranean diet was associated with beneficial changes in gut microbiota composition, including increases in bacteria that produce short-chain fatty acids.

Keep ultra processed foods to a minimum: High intakes of ultra processed foods have been linked with reduced microbial diversity and higher inflammation markers in observational research.

Stay hydrated and mindful of meal timing. Adequate water supports gut motility, and regular eating patterns can help maintain microbial balance.

When diet may need additional support

For most adults, food first is the best foundation. Some situations where additional support may be considered include:

• Periods of high stress or disrupted eating routines
• Travel that limits access to varied fresh foods
• Following a course of antibiotics, where the microbiome may take time to rebalance
• Older adults, where appetite and nutrient absorption can change with age

Where dietary intake is inadequate, a supplement may be considered to help maintain healthy gastrointestinal immune function and support the immune system. Blackmores Gut Immune Biotic is a tablet formulation that contains vitamin C (500mg, from ascorbic acid, calcium ascorbate and sodium ascorbate), zinc (7mg, from zinc gluconate) and Saccharomyces cerevisiae cell wall extract (125mg dry concentrate).

The vitamin C and zinc each contribute to the normal function of the immune system. Saccharomyces cerevisiae cell wall extract is a yeast derived beta-glucan that has been the subject of clinical research for its interactions with innate immune cells.

A randomised trial published in Nutrition involving community dwelling adults aged 50 to 70 reported that participants taking yeast beta-glucan over 90 days experienced fewer medically confirmed upper respiratory tract infections and shorter symptom duration than those receiving placebo. Blackmores Gut Immune Biotic is for adults only.

Supplements work best alongside, not instead of, a varied diet. If you're considering one, talk to a healthcare professional, particularly if you have a medical condition or take prescription medications.

Key takeaways: simple dietary habits for long term health

A handful of consistent habits can shape the gut and immune environment over time:

• Aim for a wide variety of plant foods across the week
• Include a daily source of fermented food where possible
• Choose colourful fruits and vegetables across the week for polyphenol variety
• Keep ultra processed foods to a minimum
• Stay hydrated and maintain a regular eating pattern

Diet is one of the most accessible ways to support gut microbiota and immune function. The changes can feel small, but consistency builds over time.

Frequently asked questions

What foods are best for gut health?

A varied range of plants is the strongest dietary signal for gut microbial diversity. Fibre rich foods (oats, legumes, vegetables, wholegrains), fermented foods (yoghurt, kefir, kimchi, sauerkraut) and polyphenol rich foods (berries, olive oil, dark chocolate, green tea) each support the gut microbiome in different ways.

Can what I eat support my immune system?

Diet contributes the nutrients the immune system relies on, including vitamin C, vitamin D, zinc, selenium and omega-3 fatty acids. A varied, plant-forward eating pattern with adequate protein and fibre provides a strong foundation. Diet is one of several lifestyle factors, alongside sleep, physical activity and stress management.

How much fibre should I eat each day?

The Australian Adequate Intake is 25g of fibre per day for women and 30g for men. Higher targets of 28g for women and 38g for men are suggested to reduce chronic disease risk. Most Australian adults fall short of these levels, so increasing wholegrains, legumes, fruits and vegetables is a useful starting point.

Are fermented foods better than supplements?

They serve different purposes. Fermented foods provide variable amounts of microbes and additional nutrients, while supplements deliver specific, measured ingredients at known doses. Both can play a role, depending on individual circumstances.

How long does it take to see changes from diet?

The gut microbiome can shift within days of dietary changes, but more meaningful patterns of diversity tend to develop over weeks to months. Consistency is more useful than perfection.

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 a personalised assessment and recommendations. Supplements should not replace a balanced diet.