D2.541 - Healthy and unhealthy plant-based dietary patterns and asthma: a systematic review using validated dietary indices

Plant-forward dietary patterns, including vegetarian, vegan and planetary health diets, are associated with reduced systemic inflammation and improved metabolic health. However, plant-based diets are heterogeneous. Validated dietary indices, including the Plant-Based Diet Index (PDI), healthy and unhealthy PDI (hPDI, uPDI) and the Planetary Health Diet Index (PHDI), capture both the degree of plant-based eating and the nutritional quality of plant foods. The aim of this systematic review was to evaluate associations between adherence to plant-forward dietary patterns, assessed using validated dietary indices, and asthma-related outcomes.

PubMed/MEDLINE, Embase, Web of Science and Cochrane were systematically searched from inception to October 2025 for interventional and observational studies evaluating associations between plant-forward dietary patterns and asthma-related outcomes. Search terms combined plant-based, vegetarian, vegan and planetary health diet concepts with asthma, wheeze and airway inflammation. Studies were included only if plant-forward diets were quantified using validated plant-based dietary indices. Titles and abstracts were screened independently by two reviewers, followed by full-text review and data extraction. The review followed PRISMA methodology. A total of 143 records were identified across databases and four studies met the inclusion criteria.

Four observational studies were included (three prospective cohorts and one cross-sectional study). No interventional studies using validated plant-based dietary indices were identified.Study 1 (NHANES, n>32,000 adults) showed a significant inverse association between PHDI and asthma prevalence, partly mediated by body mass index.Study 2 (school-aged children, n=660) found higher PHDI to be associated with lower airway inflammation measured by exhaled nitric oxide, with effects limited to children without overweight or obesity.Study 3 (elderly women, n≈5,700) demonstrated that higher adherence to overall and healthy plant-based diets was associated with a reduced incidence of asthma symptoms over time, largely mediated by body mass index.Study 4 (UK Biobank, n>160,000) reported that higher PDI and hPDI were associated with a reduced risk of adult-onset asthma, whereas higher uPDI was associated with increased risk.

Despite the use of different validated dietary indices capturing both the degree of plant-based eating and the nutritional quality of plant foods, healthy plant-based indices were associated with lower asthma prevalence, lower risk of incident asthma and reduced airway inflammation, whereas unhealthy plant-based indices were associated with higher asthma risk.All available evidence is observational, highlighting a critical gap and the need for well-designed dietary intervention trials in asthma.