This was a single-center prospective observational cohort study conducted in Poland in the context of routine metabolic outpatient care. The study assessed selected metabolic, biochemical, oxidative-stress, inflammatory, and body-composition parameters in individuals with overweight or obesity undergoing standard lifestyle-based body weight reduction management. Participants with BMI > 25 kg/m² were followed before and after body weight reduction, while individuals with normal body weight served as a comparison group. The weight reduction management included individualized dietary recommendations, physical-activity guidance, health education, regular follow-up visits, fasting blood sampling, and body-composition assessment. The aim of the study was to evaluate whether body weight reduction is associated with changes in metabolic and biochemical parameters, with particular attention to glucose and lipid metabolism, oxidative stress, inflammatory markers, adipokines, cytokines, and body-composition changes.

This was a single-center prospective observational cohort study conducted at the Medical University of Silesia in Katowice, Poland, and in a metabolic outpatient clinic in Miasteczko Śląskie, Poland. The study was designed to evaluate the effect of body weight reduction on selected metabolic, biochemical, oxidative-stress, inflammatory, and body-composition parameters in individuals with overweight or obesity.

The study was conducted in the context of routine metabolic outpatient care. Participants with overweight or obesity received standard lifestyle-based body weight reduction management, including individualized dietary recommendations, physical-activity guidance, health education, and regular follow-up visits. The investigators did not assign participants to an investigational medicinal product, medical device, dietary supplement, surgical procedure, pharmacological intervention, or experimental therapy. The study prospectively observed participants receiving routine lifestyle-based weight reduction management and assessed changes in clinical and laboratory parameters before and after body weight reduction.

The approved study protocol planned the inclusion of individuals with overweight or obesity and a normal-weight comparison group. Participants with BMI > 25 kg/m² were evaluated in relation to body weight reduction, while individuals with normal body weight served as a comparison group for selected baseline analyses. Patients with overweight or obesity were assessed by medical examination, dietary and clinical questionnaires, anthropometric measurements, body-composition analysis, and fasting blood sampling. Body-composition analysis included assessment of body weight, fat mass, fat-free mass, skeletal muscle mass, total body water, visceral fat, and related parameters. Blood samples were collected for biochemical analyses, including markers of glucose metabolism, lipid metabolism, oxidative stress, antioxidant status, inflammatory markers, adipokines, cytokines, chemokines, growth factors, and selected cardiovascular-risk parameters.

Participants with overweight or obesity were followed during standard body weight reduction management until clinically relevant weight reduction or achievement of optimal body weight. According to the original study documentation, assessments were planned before the start of weight reduction, after approximately 10% body weight reduction, and after approximately 20% body weight reduction or achievement of target body weight. Follow-up visits included body weight measurements, waist and hip circumference measurements, dietary counselling, education regarding caloric intake, and motivation to continue lifestyle modification.

The primary objective of the study was to assess whether body weight reduction in individuals with overweight or obesity is associated with changes in selected metabolic and biochemical parameters. Secondary objectives included evaluation of oxidative-stress and antioxidant-status parameters, glucose and lipid metabolism, inflammatory markers, adipokines, cytokines, and body-composition changes. The study also aimed to assess relationships between biochemical parameters and body-composition indices before and after body weight reduction.

The study was approved by the Bioethics Committee of the Medical University of Silesia in Katowice, Poland. All participants received information about the study and provided written informed consent before participation. This ClinicalTrials.gov record is submitted retrospectively to meet journal publication requirements and to provide transparent public information about the completed study.

Inclusion Criteria:

• Adults aged 18-85 years
• BMI > 25 kg/m²
• Overweight or obesity diagnosed on the basis of medical examination and body-composition assessment
• Participation in routine lifestyle-based body weight reduction management in a metabolic outpatient clinic
• Written informed consent to participate in the study

Exclusion Criteria:

• Lack of informed consent
• Severe hepatic insufficiency
• Severe renal insufficiency
• Severe respiratory insufficiency
• Severe circulatory insufficiency
• Disturbances of consciousness
• Treatment-resistant depression
• Chronic alcohol abuse
• Pregnancy
• History of serious nervous system injury
• Implanted cardiac pacemaker
• Pharmacological treatment affecting glucose and/or lipid metabolism
• Incomplete follow-up or incomplete laboratory data

Adults with overweight or obesity who received routine lifestyle-based body weight reduction management in a metabolic outpatient clinic in Miasteczko Śląskie, Poland, and who provided written informed consent for participation in the study.

Individual participant data will not be made publicly available because of privacy and confidentiality restrictions, limitations of the original informed consent, and the retrospective registration of this completed study. De-identified aggregate data or non-identifiable datasets may be made available from the investigators upon reasonable request, subject to institutional approval and applicable data protection regulations.