Sex-Specific Responses to Intermittent Fasting: A Narrative Review Across Physiological, Clinical, and Psychosocial Contexts

Background/Objectives: Intermittent fasting (IF) has gained increasing attention as a nutritional strategy to improve metabolic health, body composition, and disease-related outcomes. However, its effects are often interpreted as broadly uniform, despite growing evidence that biological sex may modulate fasting responses. This narrative review examines sex-specific differences in the physiological, endocrine, clinical, and psychosocial effects of IF in women and men. Methods: We conducted a narrative synthesis of human and preclinical evidence addressing IF protocols, mechanisms, benefits, adverse effects, and sex-related differences. Particular attention was given to substrate metabolism, hormonal regulation, neuroendocrine sensitivity, energy availability, exercise performance, chronic disease management, aging-related outcomes, and psychological or behavioral responses. Results: The available literature suggests that women and men share several beneficial responses to IF, including improvements in body composition and cardiometabolic markers, but may differ in the magnitude, tolerability, and mechanistic basis of these effects. Women appear to show greater sensitivity of reproductive and neuroendocrine function to energetic stress, particularly under conditions of low energy availability, high exercise load, or reproductive vulnerability. In contrast, men may exhibit preserved functional outcomes despite measurable endocrine adaptations, including changes in testosterone dynamics. Across both sexes, responses vary according to fasting protocol, nutritional adequacy, baseline metabolic status, life stage, and clinical context. Conclusions: Current evidence supports a sex-informed and context-specific interpretation of IF rather than universally applicable fasting prescriptions. Direct sex-comparative studies remain scarce, and many conclusions are inferred from parallel male and female studies. Future research should integrate sex as a core biological variable in precision nutrition and fasting-based interventions.