Effects of Prior Fasting on Fat Oxidation during Resistance Exercise

Area of Science:

• Exercise Physiology
• Nutritional Biochemistry
• Metabolic Studies

Background:

• Carbohydrate (CHO) utilization increases with exercise intensity.
• Pre-exercise food intake influences fuel selection; fasting generally promotes fat metabolism.
• Limited data exists on the impact of fasting on fuel utilization during resistance exercise.

Purpose of the Study:

• To investigate the effects of resistance training in a fasted state versus postprandial state on fat and carbohydrate utilization.
• To compare substrate utilization during resistance exercise under different pre-exercise nutritional conditions.

Main Methods:

• Twelve female NCAA Division 1 athletes completed two resistance training sessions: one fasted (10 hours) and one postprandial (after a standardized meal).
• Fuel utilization was assessed by measuring respiratory exchange ratio (RER) and metabolic equivalents (METs).
• Exercises included bench press, back squat, and military press at 60% of 1-repetition maximum.

Main Results:

• The mean fasted RER was significantly lower than postprandial RER during back squat and military press, indicating greater fat utilization.
• No significant differences were observed in METs, RPE (Rate of Perceived Exertion), or HR (Heart Rate) between fasted and postprandial conditions.
• Bench press did not show a significant difference in RER between the two conditions.

Conclusions:

• Resistance exercise performed in a fasted state appears to promote greater reliance on fat metabolism compared to carbohydrate metabolism.
• Nutrient timing may play a role in modulating substrate utilization during resistance training.