Fasted exercise, or working out before eating breakfast, frequently resurfaces on social media with claims that it is the most effective way to lose body fat. The concept is based on research showing that aerobic exercise in a fasted state increases fat oxidation during the workout. However, a 2017 systematic review found no significant long-term difference in body fat loss between fasted and fed exercise programs. The body appears to compensate over time, reducing fat burning after meals and adjusting overall daily energy expenditure. While eating carbohydrates and protein around workout times can support performance, whether consumed before or after exercise has limited impact. Current evidence does not demonstrate that fasted training is superior for weight loss or sports performance, though it does not cause major problems either. What truly matters is simply doing regular exercise, regardless of meal timing.
Research Findings on Fat Loss and Body Composition
Supporters of fasted exercise argue it leads to better body composition changes, especially fat loss. Studies show that exercising before eating increases fat oxidation at a single point in time compared to exercising after a meal. However, this short-term effect does not translate into long-term fat loss. A 2017 systematic review revealed that fasted exercise training programs do not result in greater body fat reduction over time. The body compensates by reducing fat burning after eating and potentially lowering total daily energy expenditure. Additionally, research suggests that eating more protein in the morning may improve body composition, but this benefit relates to daily meal timing rather than proximity to exercise sessions.
Impact on Performance and Practical Considerations
Eating before exercise clearly improves performance in activities lasting over 60 minutes, but has little effect on shorter workouts. A survey of nearly 2,000 endurance athletes found that non-professionals are more likely to exercise fasted compared to professionals. Limited research on resistance training shows no significant difference in muscle strength, size, or lean body mass whether training fasted or fed. Potential drawbacks include increased hunger after fasted workouts, which may lead to poor food choices, and some people experience headaches or nausea. However, others report feeling great exercising fasted. Ultimately, consistency in exercising matters most, not whether you eat beforehand.
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