What this Trial Is About

The goal of this observational study is to evaluate whether preoperative fat-free mass predicts post-operative weight loss in patients undergoing Roux-En-Y gastric bypass. The primary objective of this study is to evaluate whether preoperative fat-free mass predicts weight loss in the two years following RYGB. The investigators will collect the following data, assessed as part of routine follow-up: * height, weight, hip and waist circumferences * body composition by bioimpedance analysis and dual energy-X-ray absorptiometry * Muscle strength and physical activity * Nutritional parameters: resting energy expenditure, eating behavior and digestive tolerance", plasma micronutrient status. . * Cardiovascular risk factors: fasting glucose, blood levels of Hb1Ac, triglycerides, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, blood pressure * Co-morbidities: joint pain and arthritis, sleep apnea, gastro-oesophageal reflux, metabolic dysfunction-associated fatty liver disease (MAFLD), cancer, stroke, heart attack. Quality of life: quality of life by the "Bariatric Analysis and Reporting Outcome (BAROS) questionnaire", symptoms of dumping syndrome by the "Sigstad diagnostic score system" Birthdate, birthweight and term of their children

Can Pre-operative Lean Mass Predict Weight Loss After Roux-en-Y Gastric Bypass?