Speaker's Highlight

• Don Sin University of British Columbia, St. Paul Hospital (Canada)
  Kenneth R. Chapman Toronto General Hospital Research Institute (Canada)
• Parameswaran Nair McMaster University (Canada)
  Carolyn Calfee UCSF (U.S.A.)
• Gregory P. Downey University of Colorado School of Medicine (U.S.A.)
  David A. Schwartz University of Colorado School of Medicine (U.S.A.)
• Neil Schluger Tuberculosis Control Branch, California Department of Public Health (U.S.A.)
  Nick Kim Critical Care & Sleep Medicine, University of California San Diego (U.S.A.)
• Nicola Hananiah Baylor College of Medicine (U.S.A.)
  Jae-Joon Yim Seoul National University College of Medicine (Republic of Korea)
• Koichiro Asano Tokai University School of Medicine (Japan)
  Diahn-Warng Perng Taipei Veterans General Hospital (Taiwan)
• Konstantinos Kostikas University of Ioannina (Greece)
  Karin Klooster University Medical Center Groningen (Kingdom of the Netherlands)

• The Gut-Lung Axis in Respiratory Health and Disease

  Respiratory health is shaped by more than the airways alone. The digestive tract, immune system and lung communicate continuously through microbial metabolites, inflammatory signals and shared mucosal defences. This relationship, known as the gut–lung axis, is becoming increasingly relevant to asthma, chronic obstructive pulmonary disease (COPD), respiratory infection and treatment research.

  For clinicians and researchers attending an APSR and KATRD-connected congress, the subject offers a useful bridge between gastroenterology, immunology, nutrition and respiratory medicine. It also has practical relevance in Australia, where bushfire smoke, urban air pollution, dietary change and unequal access to healthcare can influence respiratory outcomes.

  Why the gut matters to breathing

  The intestine contains trillions of microorganisms that help digest fibre, produce vitamins and train immune responses. Short-chain fatty acids, including acetate, propionate and butyrate, are produced when beneficial bacteria ferment dietary fibre. These compounds can influence regulatory immune cells and may help maintain a less inflammatory response in the lungs.

  Communication also travels in the opposite direction. Respiratory infections, air pollution and medicines may alter gut microbial communities through swallowed airway secretions, systemic inflammation or changes in appetite and metabolism. Antibiotics can reduce microbial diversity, while corticosteroids and other treatments may affect immune and metabolic pathways without producing the same effects in every patient.

  This does not mean that a single “healthy” microbiome has been identified. Microbial composition varies with age, geography, genetics, diet, medication use and existing disease. The most useful clinical focus is therefore on function, resilience and measurable health outcomes rather than a simple list of supposedly good or bad bacteria.

  Microbiome pathways in asthma and COPD

  Research has linked early-life microbial exposure, antibiotic use and dietary patterns with the development or severity of asthma. The findings suggest that immune maturation in the gut may influence airway hyper-responsiveness and allergic inflammation. However, associations do not prove that microbiome changes cause asthma, and commercial microbiome tests cannot currently diagnose or guide routine asthma treatment.

  In COPD, smoking, inactivity, undernutrition, recurrent infection and repeated antibiotic exposure may interact with gut and lung inflammation. Some studies report reduced microbial diversity or altered metabolite profiles in people with more severe disease. These observations may eventually support better risk assessment, but inhaled therapy, smoking cessation, pulmonary rehabilitation, vaccination and management of exacerbations remain central to care.

  Respiratory infections provide another area of interest. A balanced intestinal immune environment may support the body’s response to viral and bacterial threats, while severe infection can disturb gut integrity and promote systemic inflammation. Studies of probiotics, prebiotics and faecal microbial interventions are still developing, with results varying by organism, dose, patient group and clinical endpoint.

  Food, fibre and Australian life

  The most practical way to support microbial health is usually a varied diet containing vegetables, legumes, fruit, whole grains, nuts and seeds. These foods provide fermentable fibre and plant compounds that support microbial diversity. In Australia, this approach can be adapted to familiar options such as rolled oats, lentils, chickpeas, barley, leafy greens, apples, citrus, macadamias and seasonal produce from local supermarkets or farmers’ markets.

  Eating patterns are influenced by cost, time, culture and location. A household in Melbourne may have different access to fresh food from a remote community or a regional town, while shift work in Sydney, Perth or Brisbane can make regular meals difficult. Nutrition advice should recognise food insecurity and cultural preferences rather than presenting an expensive supplement as the main route to better respiratory health.

  Air quality is another local factor. During bushfire seasons, smoke exposure can worsen asthma and COPD symptoms, increase emergency presentations and add inflammatory stress to the respiratory system. The gut–lung connection does not replace practical protection: checking official air-quality alerts, reducing outdoor exertion during smoke events and following an individual asthma or COPD action plan are more immediate measures.

  Evidence, supplements and clinical boundaries

  Fermented foods, dietary fibre and probiotic products are often promoted as ways to improve immunity. Some trials have found modest benefits for selected outcomes, while others have shown no meaningful effect. Products differ greatly in strains, storage conditions and dose, so results from one formulation cannot automatically be applied to another.

  Australian consumers also encounter a regulatory distinction between foods, complementary medicines and therapeutic goods. Products listed with the Therapeutic Goods Administration may meet manufacturing and labelling requirements, but listing does not establish that a supplement prevents asthma, treats COPD or replaces prescribed medicine. Claims should be assessed carefully, particularly when they imply protection from infection or promise to “repair” the microbiome.

  Clinicians should review antibiotic exposure, gastrointestinal symptoms, diet quality, weight change and medication use as part of a broader respiratory assessment. Probiotic or fibre interventions may be reasonable in selected settings, but they require attention to immune status, severe illness, central venous access and other risks. Patients should not stop inhalers, oxygen or antimicrobial therapy in favour of unproven microbiome products.

  Priorities for respiratory practice

  A clinically useful approach links emerging science with established respiratory care. Research should measure outcomes that matter to patients, such as exacerbation frequency, lung function, symptom control, quality of life and hospital admission, rather than relying only on changes in stool bacteria. Studies also need to include older adults, children, Aboriginal and Torres Strait Islander communities, people in rural areas and patients with multiple chronic conditions.

  Australia’s healthcare system offers opportunities for collaboration across specialist clinics, general practice, public hospitals and community services. Medicare-supported consultations, pulmonary rehabilitation and vaccination programs can provide a foundation for prevention, while Australian research centres can contribute data on smoke exposure, antimicrobial use and local dietary patterns. Any new intervention must be affordable, culturally safe and practical outside major cities.

  Key priorities include:

  • Encourage a fibre-rich, varied eating pattern that reflects budget, culture and local food access
  • Treat asthma, COPD and respiratory infections according to current evidence-based guidelines
  • Record antibiotic exposure, dietary concerns and gastrointestinal symptoms during relevant respiratory reviews
  • Interpret probiotic, prebiotic and microbiome claims cautiously, especially when products are marketed online
  • Include bushfire smoke and urban air pollution in respiratory self-management planning
  • Design Australian studies with rural, remote and First Nations communities represented
  • Measure patient outcomes alongside microbiome composition and inflammatory biomarkers

  The gut–lung axis is best understood as a promising framework rather than a standalone treatment. It explains how nutrition, microbial metabolism, immunity, medication and environmental exposure can intersect, while reminding clinicians that complex respiratory disease rarely has one cause. The next practical step is to add a brief diet, antibiotic and gastrointestinal history to the next respiratory consultation and record it alongside standard symptom and exacerbation measures.

  Richard Russell Nuffield Department of Clinical Medicine, University of Oxford (United Kingdom)
• Mona Bafadhel King’s College London (United Kingdom)
  David Jackson Guy’s and St Thomas’ Hospital, King’s College London (United Kingdom)
• James Chalmers University of Dundee (United Kingdom)
  David Price University of Aberdeen (United Kingdom)