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 Asthma and Allergic Inflammation

  Respiratory medicine has long treated the lungs as an isolated organ, but emerging research points to a constant biochemical conversation between the gastrointestinal tract and the airways. In asthma and allergic rhinitis, this cross-talk appears to shape the intensity of inflammation, the pattern of symptoms, and even the response to inhaled therapies. Recognising the gut-lung axis as a clinical reality opens new avenues for both prevention and adjunctive care.

  For clinicians practising in Australia, where roughly one in nine people reports a current asthma diagnosis and the Melbourne thunderstorm asthma event of 2016 highlighted the fragility of respiratory health, the microbiome perspective offers a useful framework. It bridges the patient's diet, antibiotic history, and early life environment with the day-to-day burden of wheeze, cough, and airway hyperresponsiveness.

  The gut-lung axis as a biological concept

  The term "gut-lung axis" describes a two-way communication network linking the intestinal microbiota, mucosal immunity, and the respiratory tract. Microbial metabolites, immune cells primed in the gut, and signalling molecules travel through the bloodstream and lymphatic system, reaching the airways. Conversely, inflammatory signals originating in the lung can alter gut permeability and microbial composition.

  Dysbiosis in the gut, whether from repeated antibiotic courses, a low-fibre Western diet, or gastrointestinal disease, has been associated with worse allergic airway outcomes in observational cohorts. Researchers at the Woolcock Institute in Sydney have contributed to work describing how reduced microbial diversity in early infancy tracks with later wheeze, supporting the case for a developmentally embedded link between the two mucosal systems.

  Microbial metabolites and immune regulation

  Short-chain fatty acids such as butyrate, propionate, and acetate are produced when gut bacteria ferment dietary fibre. These molecules reach systemic circulation and act on lung-resident immune cells, encouraging regulatory T-cell development and dampening Th2-driven inflammation. The clinical signature of asthma, namely eosinophilic inflammation and IgE production, appears to soften in settings where SCFA levels are higher.

  Animal models confirm the mechanism: mice fed high-fibre diets develop less airway hyperresponsiveness after allergen challenge. Human data are more nuanced, but cohort studies across Australia and Europe consistently link fibre intake, measured through food frequency questionnaires, with better lung function and fewer exacerbations.

  Diet, fibre and the Australian plate

  National nutrition surveys show that most Australian adults fall short of the recommended 30 grams of daily fibre, with average intake closer to 20 grams. The gap matters for the gut-lung axis. Replacing processed snacks with wholegrains, legumes, fruits, and vegetables shifts the microbiota toward SCFA-producing species within weeks.

  In coastal cities such as Sydney, Brisbane, and Perth, access to fresh produce is generally strong, yet convenience foods dominate many household baskets. Public health messaging from the Heart Foundation and from accredited practising dietitians frames fibre as cardioprotective, and the same evidence base now extends to respiratory benefit. For Aboriginal and Torres Strait Islander communities, food security remains a pressing concern, and tailored nutrition programs are an underexplored lever for reducing asthma burden in regions where respiratory outcomes lag behind the national average.

  Early life programming

  The first thousand days of life are a critical window for microbiome assembly. Birth mode, breastfeeding, exposure to siblings and pets, and antibiotic use all shape the founding bacterial populations. In Australian birth cohorts, infants delivered by caesarean section or treated with multiple antibiotic courses in the first year show higher rates of sensitisation and later asthma.

  Promoting vaginal seeding where appropriate, encouraging exclusive breastfeeding where possible, and prescribing antibiotics judiciously in paediatrics are not merely gut-health strategies; they may reduce lifetime respiratory risk. The Australian Society of Clinical Immunology and Allergy has acknowledged microbiome research in its infant feeding and allergy prevention position statements, giving clinicians an authoritative reference for family counselling.

  Probiotics, prebiotics and clinical trials

  Supplementing with live bacteria or feeding existing microbes has been tested in asthma with mixed results. Meta-analyses suggest modest benefits for reducing eczema in early life, but the effect on established asthma is smaller. Strain selection, dose, and timing of intervention likely explain the variability.

  Trials conducted in Australian centres have generally used Lactobacillus rhamnosus GG or Bifidobacterium species, often in combination with prebiotic oligosaccharides. While not a replacement for inhaled corticosteroids, these adjuncts may support immune tolerance in selected patients, particularly during the preschool wheeze phase, and they rarely interfere with conventional preventer therapy.

  The Australian environment and respiratory risk

  Australia presents a unique respiratory landscape. Ryegrass and other introduced pasture pollens fill the air across the south-east, dust storms sweep through inland regions, and the recurring bushfire smoke of recent summers challenges even healthy lungs. The 2019–2020 Black Summer fires exposed millions of people to hazardous particulate matter, with measurable increases in asthma-related hospitalisations across New South Wales and Victoria.

  Against this backdrop, the gut-lung axis offers a counterpoint. Building microbial resilience through diet, judicious antibiotic use, and targeted supplementation may help buffer the airway against environmental insults. Research groups in Melbourne and Adelaide are now combining air quality monitoring with microbiome sampling to understand these interactions more precisely.

  Translating the evidence into clinical care

  For the practising clinician, the gut-lung axis is a layer of context rather than a standalone treatment. Taking a dietary history, reviewing antibiotic exposure, and discussing fibre intake can complement standard asthma action plans. Where patients ask about supplements, evidence-based strain selection and realistic expectations about effect size are important.

  Referral to an accredited practising dietitian may benefit patients with poorly controlled asthma and concurrent gastrointestinal symptoms, since the two often coexist. Where research remains uncertain, sharing that uncertainty honestly builds trust and keeps the door open for shared decision-making.

  Australian patients are increasingly curious about microbiome science, and the clinical encounter is a chance to translate complex findings into practical, culturally appropriate advice. Over the next decade, integrating gut-lung axis insights with pharmacological care may help reduce the personal and economic toll of allergic airway disease across the country.

  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)