Metabolic and Neuroendocrine Responses to Intermittent Fasting in Obesity

Background and Objectives: Intermittent fasting (IF) has emerged as a nutritional strategy capable of modulating circadian alignment, metabolic efficiency, and neuroendocrine regulation in individuals with obesity. Among the neurobiological mediators potentially involved, Orexin-A-a hypothalamic neuropeptide regulating arousal, appetite, and energy balance-may represent a key link between fasting patterns and metabolic homeostasis. This study aimed to evaluate the long-term metabolic and neuroendocrine effects of two intermittent fasting protocols, time-restricted feeding (16:8) and alternate-day fasting (5:2), compared with a hypocaloric Mediterranean diet used as a reference condition. Materials and Methods: Thirty adults with obesity (aged 20-40 years) were allocated to one of three dietary interventions-low-calorie Mediterranean diet, IF 16:8, or IF 5:2-based on habitual dietary patterns and followed prospectively for 12 months. Anthropometric parameters, metabolic indices, inflammatory markers (CRP, TNF-α, IL-6, IL-10), and circulating Orexin-A concentrations were assessed at baseline and at three-month intervals (T0-T3). Results: Both intermittent fasting protocols induced more rapid improvements in body mass index, adiposity, lipid profile, fasting glucose, and inflammatory markers compared with the Mediterranean diet. Among the IF strategies, the 16:8 regimen showed the most consistent and physiologically coherent pattern of adaptation, characterized by a progressive and sustained increase in Orexin-A levels. This response was strongly associated with enhanced metabolic flexibility, reduced systemic inflammation, and improved energy regulation over time. In contrast, the 5:2 protocol produced more variable metabolic and neuroendocrine responses, likely due to alternating cycles of marked caloric restriction and compensatory intake. Conclusions: Intermittent fasting, particularly the 16:8 time-restricted feeding protocol, appears to be an effective and sustainable chrononutritional strategy for obesity management. By reinforcing circadian organization, improving inflammatory balance, and activating orexinergic pathways, the 16:8 model emerges as a promising intervention to address key metabolic and neuroendocrine dysfunctions associated with obesity.