Fasted vs Fed Aerobic Exercise and Body Composition: A 4-Week RCT Under Caloric Restriction
Schoenfeld BJ, Aragon AA, Wilborn CD, Krieger JW, Sonmez GT
Evidence is still building up
Summary
In 20 healthy young women (10 per group) performing 60 minutes of aerobic exercise 3 times/week for 4 weeks while all followed a caloric deficit, reductions in body weight and fat mass were similar between fasted and fed groups, suggesting the driver is total energy balance rather than fasted vs fed state.
Key findings
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Reductions in body weight and fat mass were similar between fasted and fed groups
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Suggests total energy balance, not pre-exercise fasted/fed state, drives fat-loss differences
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A direct comparison RCT with all participants on a caloric deficit
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n=20 over 4 weeks is small, but as a direct RCT with body-composition outcomes the confidence is moderate
Related research
Fasted vs Fed Exercise for Body Composition: A Systematic Review and Meta-Analysis
Journal of Functional Morphology and Kinesiology, 2017
A meta-analysis pooling 5 studies (n=96) comparing fasted vs fed exercise found trivial-to-small effect sizes for body weight and body composition, with no clear evidence that fasted exercise is superior.
Fat and Carbohydrate Metabolism in Fasted vs Fed Aerobic Exercise: A Systematic Review and Meta-Analysis
British Journal of Nutrition, 2016
A meta-analysis showing that fasted aerobic exercise acutely increases fat oxidation during exercise compared with fed exercise. However, this acute difference in substrate use does not translate into long-term differences in body fat or composition, which depend on total energy balance.
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