This study aimed to evaluate the effects of Mediterranean diet education on sleep quality, physical activity levels, blood parameters, and anthropometric measurements among shift-working nurses.

Primary outcomes: Change in Mediterranean diet adherence and sleep quality scores from baseline to post-intervention.

Secondary outcomes: Changes in physical activity levels, anthropometric indices (e.g., BMI, waist-to-hip ratio), and blood parameters (fasting glucose, insulin, HOMA-IR, lipid profile).

Background Shift work misaligns endogenous circadian rhythms with environmental light-dark cycles, predisposing workers to poor sleep, metabolic dysregulation, weight gain and cardiometabolic disease. Observational and experimental evidence indicates that dietary patterns rich in plant foods, monounsaturated fats and lean proteins-exemplified by the Mediterranean diet (MedDiet)-can attenuate inflammation, improve lipid and glycaemic profiles, and enhance subjective well-being. Educational interventions that reinforce MedDiet principles may therefore represent a pragmatic, low-risk strategy to mitigate health risks in shift-working nurses.

Study Desing Design: Single-group, pre-post intervention study Setting: Private general hospital in Muğla, Türkiye Sample Size: 130 nurses (≈80 % women) employed in rotating shifts, aged 18-55 y Allocation: Not applicable (no comparison arm)

Participant Eligibility Inclusion Criteria Registered nurse working ≥3 rotating shifts per month at the study hospital Age 18-55 years Written informed consent Exclusion Criteria Pregnancy or lactation Current participation in another lifestyle or drug trial Diagnosed sleep disorder requiring pharmacotherapy Medical condition necessitating therapeutic diet incompatible with MedDiet principles Inability to attend ≥75 % of education sessions

Intervention Mediterranean Diet Education Programme (Weeks 1-4) Format: Four weekly face-to-face group sessions (60 min each) delivered by a registered dietitian trained in behavioural counselling.

Content:

Session 1: MedDiet pyramid, portion guidance, meal timing for shift workers Session 2: Practical meal planning; reading food labels; healthy cafeteria choices Session 3: Strategies to increase fruit, vegetable, legume and whole-grain intake; recipe demonstrations Session 4: Reducing ultra-processed foods, sugar-sweetened beverages and saturated fats; sustaining behaviour change Materials: Printed handbook (pyramid graphic, shopping lists, sample menus), online discussion forum and weekly motivational text messages.

Fidelity: Sessions follow a standardised script; attendance recorded; 10 % of sessions audited by a second dietitian.

Participants receive no meal provision; they are encouraged to apply learned principles during all shifts. No changes are made to hospital food service.

Data Collection and Management Questionnaires are administered electronically via a secure, password-protected platform. Anthropometric measurements are performed in duplicate by trained research staff following WHO protocols. Blood draws coincide with routine occupational health surveillance to minimise burden and cost. Data are de-identified upon entry; only the principal investigator retains the re-identification key in an encrypted file.

Data analysis The analysis of the data collected in the study was performed using the SPSS 21.0 software. Descriptive statistics such as arithmetic mean, frequency, standard deviation, and percentage values were utilized in the analysis. To determine whether the data showed a normal distribution, skewness and kurtosis values were examined, and these values were found to be between -2 and +2, indicating that the data followed a normal distribution. Accordingly, parametric tests were used for comparisons between groups based on demographic information and for examining relationships between scales. To compare the pre- and post-test results of the Mediterranean diet, sleep disorders, and physical activity scales with blood parameters, the Paired-Samples T-Test was used, while comparisons by gender were conducted using the Independent-Samples T-Test. For comparisons across age groups, One-Way ANOVA was performed, and Tukey's test was applied as the post hoc analysis. Additionally, Pearson correlation analysis was conducted to determine the relationships between nurses' Mediterranean diet education and their sleep quality, physical activity levels, blood parameters, and anthropometric measurements.

The internal consistency of the Mediterranean Diet Adherence Scale, developed by Özkan Pehlivanoğlu, Hüseyin Balcıoğlu, and İlhami Ünlüoğlu, was calculated as Cronbach's α = 0.829, indicating a high level of reliability. The Pittsburgh Sleep Quality Index, developed by Buysse et al. in 1989, demonstrated satisfactory internal consistency (Cronbach's α = 0.80), test-retest reliability, and construct validity. In their 2017 systematic review of physical activity assessment in amputees, Piazza, Ferreira, Minsky, Pires, and Silva reported a reproducibility coefficient of ρ = 0.81 (95% CI = 0.79-0.82).

Outcome Measures and Time Points Primary and secondary outcomes were assessed at baseline (Week 0) and after the intervention (Week 8), unless otherwise specified.

The primary outcomes of the study were adherence to the Mediterranean diet and sleep quality. Adherence was measured using the 14-item Mediterranean Diet Adherence Screener (MEDAS), a validated tool for assessing compliance with Mediterranean dietary principles. Sleep quality was evaluated using the Pittsburgh Sleep Quality Index (PSQI), a widely used self-report instrument for assessing subjective sleep patterns and disturbances.

The secondary outcomes included physical activity level, anthropometric measurements, blood biomarkers, and adverse events. Physical activity was assessed using the International Physical Activity Questionnaire-Short Form (IPAQ-SF). Anthropometric data were collected through standardized procedures: height was measured at baseline using a stadiometer, and weight, body fat percentage, and skeletal muscle mass were evaluated at both time points using the Tanita MC-180 body composition analyzer. Waist and hip circumferences were measured with a non-elastic measuring tape.

Blood biomarkers were assessed via fasting venous blood samples collected and analyzed in the hospital laboratory. Parameters included fasting glucose, insulin, triglycerides, LDL cholesterol, HDL cholesterol, and total cholesterol. The Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) was calculated using fasting glucose and insulin values.

In addition, potential adverse events were monitored continuously throughout the study using a structured questionnaire administered at regular intervals.

Ethical Considerations Ethical approval was obtained from the Bahçeşehir University Scientific Research and Publication Ethics Committee. The study complies with the Declaration of Helsinki and relevant local regulations. Participation is voluntary; nurses may withdraw at any time without affecting employment status or access to occupational health services. The intervention poses minimal risk (education only).

Recruitment begun May 2024 and finished November 2024.

Inclusion Criteria:

• Registered nurse working ≥3 rotating shifts per month at the study hospital
• Age 18-55 years
• Written informed consent

Exclusion Criteria:

• Pregnancy or lactation
• Current participation in another lifestyle or drug trial
• Diagnosed sleep disorder requiring pharmacotherapy
• Medical condition necessitating therapeutic diet incompatible with MedDiet principles
• Inability to attend ≥75 % of education session

Individual participant data will not be shared due to ethical and privacy considerations.