Medical Nutrition in the Glucagon-Like Peptide-1 (GLP-1) Era: Protein Strategies, Micronutrient Monitoring, and Lean Mass Preservation.

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) and dual glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 agents produce substantial, sustained weight loss primarily by suppressing appetite and lowering ad libitum energy intake. While fat mass loss predominates, randomized trials with body-composition substudies indicate a clinically relevant reduction in absolute lean mass. Concurrently, baseline micronutrient inadequacies are common in people with obesity and may be exacerbated by reduced intake, nausea, or vomiting during therapy. This narrative review synthesizes evidence on energy/macronutrient dynamics, body-composition outcomes, and guideline-informed protein targets to present a practical, dietitian-led framework for care. We propose pragmatic energy floors to preserve micronutrient adequacy; daily protein intakes of ≥1.2 g/kg (up to 1.6 g/kg in appropriate adults without chronic kidney disease (CKD)) with meal-wise targets of ∼0.3-0.4 g/kg and ∼2.5-3 g leucine; a structured laboratory panel (vitamin D, B12, iron studies, folate, zinc, and thiamine in high-risk patients); and integration of progressive resistance training. We also outline monitoring schedules using dual-energy X-ray absorptiometry (DXA)/bioelectrical impedance analysis (BIA) and adaptations for special populations (older adults, type 2 diabetes, CKD, vegetarian/vegan, sarcopenic obesity). The goal is to preserve lean mass, prevent deficiencies, and optimize outcomes of GLP-1-based obesity pharmacotherapy.