Adults with excess body weight frequently experience protein-energy malnutrition, skeletal muscle loss, and micronutrient deficiencies that remain undetected by standard BMI assessments. The phenomenon affects individuals receiving glucagon-like peptide-1 receptor agonists and bariatric surgery patients, who experience substantial muscle mass reductions alongside fat loss. This paradoxical malnutrition in obesity represents a fundamental blind spot in contemporary medical practice. The finding challenges decades of clinical assumptions that equate higher body weight with adequate nutrition. For the millions using GLP-1 drugs like semaglutide for weight management, the muscle loss may compromise long-term metabolic health and functional capacity. The research underscores how our primary screening tool—BMI—fails to capture body composition nuances that determine health outcomes. This limitation becomes critical as obesity treatments proliferate without corresponding nutritional safeguards. The implications extend beyond clinical settings to public health policy, suggesting current obesity interventions may inadvertently create new forms of malnutrition. While some muscle changes may reflect beneficial adaptations to energy restriction, distinguishing adaptive responses from pathological depletion requires sophisticated assessment tools most healthcare providers lack.