The primary objective of this clinical trial is to measure the changes in body weight (kg) and waist circumference (cm) of the enrolled patients at postoperative 1 year. Secondary outcomes are improvement or remission rates of obesity-related co-morbidity (hypertension, type 2 diabetes, dyslipidemia, and sleep apnea), and the change in quality of life. Additionally, postoperative incidences of morbidity and mortality, micronutrient status, body composition, and cost-effectiveness of surgical intervention will be examined.