Overview

This prospective, observational cohort study aims to evaluate whether the use of collagen-containing supplements is associated with differences in muscle mass, body composition, and body image among patients who have undergone sleeve gastrectomy (SG). The study will be conducted at the General Surgery outpatient clinic of a private hospital in Bursa, Türkiye, between May 2026 and March 2027, and will enroll adult patients (aged 18-65 years) who meet current ASMBS/IFSO eligibility criteria for metabolic and bariatric surgery.

Participants will be naturally allocated into two observational groups based on their own choice to use or not use collagen-containing supplements; no supplement will be provided or recommended by the study team, and no intervention will be made to participants' standard clinical care. All patients will be followed according to routine clinical practice preoperatively and at 2 weeks, 1 month, 3 months, and 6 months postoperatively.

Primary outcome measures include anthropometric parameters (body weight, BMI, fat mass, fat mass percentage, fat-free mass, muscle mass, percentage of weight loss, percentage of excess weight loss, waist and hip circumference) assessed via bioelectrical impedance analysis (Tanita MC-780 MA), and body image assessed using the Turkish-validated Body Shape Questionnaire (BSQ). Secondary outcomes include biochemical parameters, comorbidities, and macronutrient intake data obtained from 3-day dietary records analyzed using the BEBİS nutrition software.

The study hypothesizes that patients using collagen-containing supplements will show significant differences in muscle mass and body composition parameters compared with non-users, and that supplement use will be significantly associated with BSQ scores. A sample size of approximately 52 participants per group was calculated using G\*Power 3.1 (one-way ANOVA, Cohen's f = 0.25, α = 0.05, power = 0.80).

Eligibility

Inclusion Criteria:

• Patients with a BMI ≥ 35 kg/m², regardless of the presence of comorbidities
• Patients with a BMI of 30-34.9 kg/m² who have an obesity-related metabolic disease and are considered eligible for surgical treatment
• Patients who have undergone metabolic and bariatric surgery (MBS) in accordance with current ASMBS/IFSO guidelines (Eisenberg et al., 2022)
• Patients under regular postoperative follow-up
• Age 18-65 years

Exclusion Criteria:

• Inflammatory bowel disease
• History of upper gastrointestinal bleeding
• Severe psychiatric disorders
• Active cancer diagnosis
• Pregnancy or breastfeeding
• Alcohol or substance dependence
• Physical limitations preventing participation in exercise