Chronic obstructive pulmonary disease (COPD) is associated with persistent airflow limitation, systemic inflammation, reduced exercise capacity, and unfavorable changes in body composition. Nutritional interventions may represent a complementary strategy to improve clinical outcomes in individuals with COPD.

This pilot randomized controlled trial evaluates the feasibility, safety, and preliminary effectiveness of an 8-week ketogenic dietary intervention in men with mild-to-moderate COPD. Participants are randomly assigned to either a supervised ketogenic diet or a control group receiving standard dietary advice. The ketogenic diet restricts carbohydrate intake and promotes nutritional ketosis, which is monitored using blood beta-hydroxybutyrate measurements.

The primary outcome is change in the FEV1/FVC ratio. Secondary outcomes include systemic inflammation assessed by C-reactive protein (CRP), phase angle measured by bioelectrical impedance analysis, functional exercise capacity assessed by the 6-minute walk test, estimated aerobic capacity, body composition, and selected biochemical safety markers. The study aims to provide preliminary evidence regarding whether a ketogenic dietary approach may improve inflammatory status, functional capacity, and physiological outcomes in individuals with COPD.

Chronic obstructive pulmonary disease (COPD) is a progressive respiratory disorder characterized by persistent airflow limitation, chronic inflammation, exercise intolerance, and alterations in body composition. In addition to pulmonary impairment, systemic manifestations such as increased inflammatory burden, skeletal muscle dysfunction, and adverse metabolic changes contribute substantially to morbidity and reduced quality of life. Nutritional interventions have therefore emerged as potential adjunctive strategies in COPD management.

Ketogenic diets are characterized by marked carbohydrate restriction, moderate protein intake, and increased dietary fat consumption, resulting in nutritional ketosis. Potential mechanisms relevant to COPD include reductions in systemic inflammation, changes in substrate utilization, reductions in adiposity, and alterations in respiratory gas exchange. However, randomized controlled studies investigating ketogenic dietary interventions in COPD remain limited.

This study is an 8-week, single-center, parallel-group pilot randomized controlled trial conducted in clinically stable men with GOLD stage I-II COPD. Participants are randomly allocated in a 1:1 ratio to either a ketogenic dietary intervention or a control group receiving standard dietary advice. The ketogenic diet is individually prescribed by a dietitian and aims to provide approximately 60-70% of total energy from fat, 15-20% from protein, and 5-10% from carbohydrates, with carbohydrate intake restricted to less than 50 g/day.

Nutritional ketosis is monitored using capillary beta-hydroxybutyrate measurements obtained throughout the intervention period. Pulmonary function is assessed using spirometry. Body composition and phase angle are measured using multifrequency bioelectrical impedance analysis. Functional exercise capacity is evaluated using the 6-minute walk test, and estimated aerobic capacity is derived from walking performance. Blood samples are collected to assess inflammatory and safety-related biomarkers, including C-reactive protein, lipid parameters, alanine aminotransferase, and creatinine.

The primary objective is to determine whether an 8-week ketogenic dietary intervention improves FEV1/FVC compared with standard dietary advice. Secondary objectives are to evaluate effects on systemic inflammation, phase angle, exercise capacity, body composition, and biochemical safety outcomes. As a pilot trial, the study is designed to generate effect-size estimates, assess feasibility and adherence, and inform the design of future larger multicenter randomized controlled trials.

Inclusion Criteria:

• Male sex
• Age between 40 and 75 years
• Clinically stable chronic obstructive pulmonary disease (COPD)
• GOLD stage I or II COPD
• No acute COPD exacerbation within the previous 3 months
• Stable pharmacological treatment for at least 4 weeks before enrollment
• Ability to complete study assessments and comply with dietary instructions
• Provision of written informed consent

Exclusion Criteria:

• GOLD stage III or IV COPD
• Uncontrolled cardiovascular disease
• Chronic kidney disease
• Severe hepatic dysfunction
• Active malignancy
• Insulin-dependent diabetes mellitus
• Participation in another dietary intervention program within the previous 3 months
• Inability to complete study assessments
• Contraindications to dietary carbohydrate restriction
• Refusal or inability to provide informed consent

Individual participant data sharing has not yet been determined. Data sharing decisions will be made after publication of the primary study results and will be subject to institutional policies, ethical considerations, participant confidentiality requirements, and applicable data protection regulations.

Blinding was not feasible because of the nature of the dietary intervention.