Adherence and Tolerability of Four Very Low-Calorie Ketogenic Diet Approaches in Adults With Obesity or Complicated Overweight

This study, called KOBE Study, looks at how well different very low-calorie ketogenic diets (VLCKD) are followed and tolerated by adults with obesity or complicated overweight in routine clinical practice. Ketogenic diets are medical nutrition therapies that greatly reduce carbohydrates and calories to promote weight loss and improve metabolic health. Several VLCKD approaches are used in clinical care, but they differ in the type of protein sources used (natural foods versus meal replacements or supplements). At present, there is limited evidence comparing these approaches in terms of adherence, side effects, satisfaction, and dropout rates. The KOBE Study is a single-center, prospective, observational study conducted during standard clinical care at a hospital nutrition clinic. Participants choose one of four VLCKD protocols based on personal preference: * diets using only natural protein foods, * natural proteins plus one protein supplement, * natural proteins plus two meal replacements, * or diets based entirely on meal replacements. All participants follow the same structured program lasting about 26 weeks (longer for individuals with severe obesity), consisting of: 1. an initial ketogenic phase, 2. a gradual reintroduction of carbohydrates, 3. a maintenance phase based on a low-glycemic index Mediterranean-style diet. Throughout the study, patients undergo routine clinical visits and assessments, including measurements of body weight, body composition, blood tests, liver imaging, and questionnaires on hunger, bowel habits, quality of life, and satisfaction with the diet. No additional tests beyond standard care are required. The main goal of the study is to compare the different ketogenic protocols in terms of: * how well patients can follow them, * how well they are tolerated, * the occurrence of side effects, * and overall satisfaction. Secondary objectives include evaluating changes in body composition, metabolic parameters, and liver health. The res