This randomized controlled study evaluates the effects of a balanced vegan diet compared with a balanced omnivorous diet on inflammatory and immune response markers and clinical asthma parameters in healthy adults and individuals with mild to moderate asthma, aged 18 to 50. Participants will follow assigned dietary plans for 12 weeks with dietitian support delivered via digital tools.

This prospective, randomized, controlled study aims to evaluate the effects of a balanced vegan diet on inflammatory and immune response markers, clinical asthma parameters, and metabolic profile in healthy adults and patients with mild to moderate asthma. The study will enroll participants aged 18 to 50 years, who will be randomly assigned to either a vegan diet intervention group or a control group following an omnivorous diet for 12 weeks.

Dietary interventions will be individually tailored by a clinical dietitian according to current national nutrition guidelines. To ensure safety and standardization, all participants will receive vitamin D supplementation (2000 IU/day), and participants in the vegan group will additionally receive vitamin B₁₂ supplementation (25-100 µg/day or weekly equivalent). Adherence to the diet will be monitored through weekly online consultations, 3-day food diaries, and digital tools.

Assessments will be performed at baseline and after 12 weeks of intervention. Evaluated parameters will include:

• Inflammatory markers: hsCRP, IL-4, IL-5, IL-13, TNF-α
• Immune function markers: lymphocyte subpopulations (CD4+, CD8+, CD4+/CD8+ ratio, Treg cells by flow cytometry/ELISA) and immunoglobulins (IgE, IgA, IgG, IgG1-IgG4)
• Respiratory function: fractional exhaled nitric oxide (FeNO), spirometry
• Anthropometric and body composition measures: body weight, body mass index (BMI), waist circumference, waist-to-hip ratio, bioimpedance body composition analysis
• Lipid profile: total cholesterol, HDL, LDL, non-HDL cholesterol, triglycerides
• Asthma symptom control: Asthma Control Test (ACT) scores The planned sample size is 280 participants, distributed across four groups (n=70 per group): healthy - omnivorous diet, healthy - vegan diet, asthma - omnivorous diet, asthma - vegan diet. However, an initial pilot phase will be conducted to assess feasibility and refine study procedures before full-scale recruitment.

Inclusion Criteria:

For all groups:

• Aged 18-30 years
• Willing to adhere to assigned dietary plan (vegan or omnivorous) for 12 weeks
• Non-smoker for at least 5 years
• Body mass index (BMI) between 18.5 and 24.9 kg/m2

For the asthma group:

• Clinical diagnosis of mild or moderate asthma (GINA criteria), made at least 12 months before enrollment
• Stable asthma status (no exacerbations or changes in therapy within the past 3 months)
• No change in pharmacotherapy during the study period

Exclusion Criteria:

• Use of systemic corticosteroids (oral or intravenous) within the past 3 months
• Ongoing biological therapy for asthma (e.g., anti-IgE, anti-IL-5, anti-IL-4R)
• Severe asthma as per GINA criteria
• Recent asthma exacerbation requiring hospitalization or steroid burst (<3 months)
• Presence of other chronic autoimmune or inflammatory diseases
• Pregnancy or lactation
• Active infection or acute illness at the time of recruitment
• Adherence to specialized exclusion diets (e.g., ketogenic, low-FODMAP)
• History of eating disorders
• Inability or unwillingness to participate in follow-up visits or comply with the protocol