At baseline, venous blood samples were collected from all eligible participants. The following biochemical parameters were analysed: serum electrolytes (mineral profile), fasting glucose, creatinine, urea nitrogen, total proteins, albumin, bilirubin, liver enzymes, C-reactive protein (CRP), total cholesterol, triacylglycerols (TAG), serum iron, active vitamin D, vitamin B12, complete blood count.

At baseline, all participants also underwent standardized anthropometric measurements, including height (cm), body weight (kg) and BMI was calculated accordingly. Body composition was assessed using bioelectrical impedance analysis with the InBody Tanita MC-780MA device. The following parameters were recorded: total body fat (kg, %), visceral fat (kg, %), skeletal muscle mass (kg, %), total muscle mass (kg, %), total body water (kg, %), sarcopenic index (kg/m²), phase angle.

To assess health-related quality of life and symptom burden, all participants completed validated questionnaires: World Health Organization Quality of Life - Brief Version (WHOQOL-BREF), Patient Assessment of Gastrointestinal Disorders - Symptom Severity Index (PAGI-SYM), Patient-Reported Outcomes Measurement Information System Global Health-10 (PROMIS-10), Patient Assessment of Upper Gastrointestinal Disorders - Quality of Life (PAGI-QoL) and Patient Health Questionnaire-15 (PHQ-15).

After the one-month intervention, participants in the VEG group repeated laboratory testing, anthropometric assessment, body composition analysis, and questionnaire evaluation. The same follow-up assessments were performed in the WD group for comparative purposes. Long-term vegans (VEG-P) did not undergo repeated measurements.

Dietary Monitoring and Adherence At study enrolment, all participants were offered a dietary consultation to improve adherence to the assigned dietary regimen. Participants were also instructed to maintain a food diary throughout the study period, which was periodically reviewed via telephone or email consultation.