Fasting and exercise: Effects on cellular adaptation, performance, and recovery

Fasting has garnered significant interest in the fields of sports and exercise physiology due to its potential to foster beneficial metabolic and cellular adaptations. This review investigates the impact of fasting on exercise performance, recovery, and cellular adaptation, with a focus on key metabolic pathways, hormonal responses, and molecular mechanisms. Various fasting strategies, such as intermittent fasting (IF), time-restricted feeding (TRF), and prolonged fasting, affect energy metabolism by shifting fuel utilization from glycogen to fatty acid oxidation and ketogenesis. These metabolic shifts are associated with enhanced insulin sensitivity, reduced inflammation, and increased autophagy, all of which contribute to cellular repair and mitochondrial function.At the cellular level, fasting activates autophagy, a critical process for muscle maintenance and mitochondrial quality control. Furthermore, fasting influences mitochondrial biogenesis through the activation of AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), which are essential regulators of energy homeostasis and endurance adaptation. Hormonal changes during fasting, including increases in growth hormone and catecholamines, alongside reductions in insulin and insulin-like growth factor-1 (IGF-1), further impact exercise metabolism and recovery dynamics. These adaptations suggest that fasting may enhance endurance performance by improving metabolic flexibility and delaying glycogen depletion. However, its effects on strength and power output are more intricate, as improper management of nutrient intake during fasting can hinder muscle protein synthesis (MPS).Fasted training has been shown to yield adaptations that benefit endurance athletes, such as enhanced fat oxidation and improved mitochondrial efficiency. Conversely, it may present challenges for strength athletes due to increased muscle protein breakdown (MPB) and delayed recovery. Post-exercise nutrition strategies, encompassing optimal protein timing and macronutrient composition, are crucial for alleviating the potential negative effects of fasting on muscle repair and performance. Additionally, ketone bodies, particularly β-hydroxybutyrate (BHB), have emerged as potential modulators of recovery due to their anti-inflammatory and antioxidant properties.While fasting represents a promising approach for metabolic enhancement, its implementation in athletic performance necessitates careful consideration of individual variability, training demands, and sport-specific objectives.