Study protocol for a non-inferiority, multicenter, randomized study to evaluate a smartphone app-based follow-up program after bariatric surgery (BELLA plus trial).

Introduction: Adherence to follow-up (FU) care after bariatric surgery is poor despite strong recommendations. In our pilot Bella trial, we demonstrated that a completely remote follow-up program via smartphone is feasible and safe for patients after bariatric surgery. Building on this, we aim to verify our results in a multicenter, randomized controlled setting.

Methods: This trial plans to enroll 410 participants undergoing primary bariatric surgery in seven German bariatric centers. Participants are randomized into two groups: a control group receiving in-person FU according to the standard in the bariatric centers, and an interventional group monitored using a smartphone application (app). The app sends standardized questionnaires and reminders regarding regular vitamin intake and exercises. The built-in messaging function enables patients to communicate remotely with medical care professionals. After one year, all participants are evaluated at their primary bariatric centers. The primary outcome is weight loss 12 months after surgery. The secondary outcomes include obesity-related comorbidities, quality of life, serum values of vitamins and minerals, body impedance analysis, visits to the emergency department or readmission, patient compliance, and medical staff workload.

Discussion: The current study is the first prospective, individually randomized-controlled, multicenter trial where a mobile application completely replaces traditional in-person visits for post-bariatric surgery follow-ups in bariatric centers.