Adherence and Persistence with GLP-1-Based Therapies: International Real-World Evidence and the Role of Nutritional and Lifestyle Support—A Narrative Review

Background/Objectives: Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have transformed type 2 diabetes mellitus (T2DM) and obesity care, with clinical trials demonstrating weight loss exceeding 15%. However, real-world effectiveness lags trial efficacy, largely owing to high discontinuation rates. We characterize the global persistence gap and propose a framework integrating Medical Nutrition Therapy (MNT) to improve adherence. Methods: We conducted a narrative review of real-world evidence from North America, Europe, Asia, and Latin America, synthesized with physiological, nutritional, and behavioral data to distinguish established contributors to discontinuation from strategies that remain partly extrapolated from related populations. Results: Global persistence varies widely: from approximately 75–80% at 12 months in reimbursed T2DM cohorts (Sweden, Denmark) to below 10% in obesity-focused or high out-of-pocket-cost settings (Poland, Colombia), with intermediate rates in the United States and United Kingdom; in several cohorts, persistence falls below 15% by 24 months. The primary drivers are gastrointestinal intolerance and economic barriers. Meal size, dietary composition, and gastric-emptying effects influence gastrointestinal tolerability; inadequate protein intake during rapid weight loss raises concern for lean mass loss. Conclusions: Pharmacotherapy alone is unlikely to sustain long-term obesity management. Narrowing the persistence gap will require an integrated care model in which structured nutritional support—targeting protein intake, micronutrient density, and gastric-sparing feeding—is systematically offered rather than treated as an optional adjunct, while recognizing that most supporting evidence is extrapolated from primary trials in obesity and cardiometabolic disease rather than derived from GLP-1–specific randomized trials.