Resistance training performed in the fasted state compared to the fed state on body composition and strength in adults: A systematic review with meta-analysis

Abstract

Introduction: Fasting has been used as a strategy to promote reduction in body fat and enhance adaptations to physical training, but there is no consensus in the literature regarding the effects of resistance training when sessions are performed while fasting. The aim was to systematically review the effects of resistance training performed in the fasted state on body composition and physical performance.

Method: We included clinical trials that comparing resistance training performed in fasted state versus fed state on fat free mass, body fat mass, muscle hypertrophy and strength in adults. The search was performed using databases, gray literature and manual search. Methodological quality was assessed using the risk of bias tool for randomized trials. The pooled effect estimates were computed from the standardized mean difference and the 95 % confidence interval using random effects models.

Results: Four studies were included, three of which were assessed as having high risk of bias. No significant differences were found between fasted and fed states in fat free mass (SMD: 0.529; 95 % CI: -0.801 to 1.859; p = 0.436), muscle hypertrophy (SMD: 0.645; 95 % CI: -0.753 to 2.042; p = 0.366), or strength (SMD: 0.415; 95 % CI: -0.399 to 1.228; p = 0.318). However, the fasted state was associated with greater changes in body fat mass (SMD: -1.001; 95 % CI: -1.970 to -0.032; p = 0.043).

Conclusion: Resistance training performed in fasted and fed states appears to have similar effects on body composition, muscle hypertrophy and strength, particularly when sessions follow an overnight fast.

Keywords: Fat free mass; Fat mass; Muscle strength; Overnight fasting; Strength training.