Pre-Exercise Protein Does Not Reduce Fat Burning During Exercise
How different doses of whey protein can influence substrate metabolism during exercise compared to fasted.
This study investigated the effects of different doses of pre-exercise protein intake on substrate metabolism, energy expenditure, and energy intake in active individuals (PMID: 378868410).
Key Points
Aim
To determine whether varying amounts of whey protein (0, 20, or 40 grams) consumed before exercise would influence fat oxidation rates and resting energy expenditure (REE) during and after exercise.
Methods
Participants: The study included 15 healthy, active adults (both males and females aged 18-35) who met the American College of Sports Medicine (ACSM) guidelines for physical activity. Exclusion criteria included known food allergies, certain medical conditions, and use of medications affecting metabolism.
Design: This was a randomised, double-blinded, placebo-controlled within-subject trial. Participants completed three experimental trials where they ingested either 0, 20, or 40 grams of whey protein 30 minutes before performing one hour of cycling at 60% of their peak power output.
Data Collection: Indirect calorimetry measured substrate oxidation during exercise. Blood samples were taken at various time points to assess metabolic responses. Additionally, participants recorded their food intake post-exercise using food diaries.
Results
Fat Oxidation: There were no significant differences in fat oxidation rates among the three protein intake conditions (p = 0.19), suggesting that pre-exercise protein does not impair fat oxidation compared to fasted exercise.
Metabolic Responses: Serum insulin levels were higher in the protein groups compared to the 0 g group (p < 0.05). Non-esterified fatty acids were higher in the fasted condition compared to both protein conditions (p < 0.05). Glucose levels were significantly lower after 15 minutes of exercise in the 20 g and 40 g conditions compared to the fasted state (p = 0.01).
Resting Energy Expenditure: Post-exercise REE was significantly elevated across all conditions (p < 0.001), with no interaction effect based on protein dose (p = 0.90).
Energy Intake: Free-living energy intake post-trial did not differ significantly between conditions (p = 0.31). Still, total energy intake over 24 hours was significantly higher in the 40 g group than the fasted group (p = 0.04).
