Metabolic Adaptation and Weight Regain in Obesity Treatment: The Central Role of Nutrition in the Era of Bariatric Surgery and GLP-1-Based Pharmacotherapy

Obesity is a multifactorial chronic disease characterized by pathological adipose tissue expansion and systemic metabolic dysfunction. This review examines metabolic adaptation—the counter-regulatory physiological response to weight loss—and its contribution to weight recidivism. Although weight reduction confers substantial clinical benefit, long-term maintenance is frequently compromised by reductions in total daily energy expenditure (TDEE) that exceed predictions based on body composition. Bariatric surgery induces profound metabolic remodeling; however, its durability may be constrained by persistent biological defense mechanisms of body weight. Similarly, GLP-1 receptor agonists have transformed pharmacological management, yet in the absence of structured nutritional intervention, lean mass loss and energetic compensation may attenuate long-term stability. We propose an integrated model in which precision nutrition, surgery, and pharmacotherapy operate synergistically. Within this framework, nutrition should assume a central regulatory role in modulating body composition, substrate partitioning, and long-term energetic homeostasis to enhance the sustainability of clinical outcomes.