Whether cardio on an empty stomach can speed up fat loss is a commonly debated fitness topic. Some believe fasted cardio is more effective at burning fat while others believe it can decrease performance and limit fat loss.
Who is right? The following will inform you of what research has to say about the topic and offer compelling reasons why fueled exercise leads to greater overall fat burn.
Cardio on an Empty Stomach Burns More Fat DURING Exercise
Two fuel sources—carbs & fats—are used to generate energy for muscle contraction during exercise. For endurance exercise performed at a moderate intensity, you obtain 50–60% of energy needed from glycogen (which is stored energy from carbs) and the rest from fats.
When you deplete glycogen stores by fasting overnight, or going several hours without refueling, fatty acids break down in the mitochondria to be used as a secondary energy source. As workout intensity increases, your reliance on carbohydrates increases as well.
In one study that tested the fat burning effect cardio on an empty stomach, six healthy men cycled for 60 minutes at a low to moderate intensity:1
Group 1-Fasted overnight before the bike ride.
Group 2- Performed the bike ride after ingesting 0.8g/kg of glucose or fructose to replenish glycogen levels 1 hour prior to the workout.
Results: After 20-30 minutes of exercise, the rate of fat burn was higher in the fasted group than in the glucose or fructose group. This trend continued throughout 50-60 minutes of exercise. There was also a higher quantity of FFAs (Free flowing fatty acids) available in the blood in a fasted state throughout the exercise.
The Take Away: This particular study suggests that more fat was burned by the group that performed MODERATE activity on an empty stomach… DURING THE EXERCISE ITSELF.
So Should You Perform Cardio on an Empty Stomach?
Research shows that people who burn fat during their workouts actually burn less fat the rest of the day.
Evidence supporting fueled exercise
Researchers from Italy investigated the contrasting reports on whether training in a fasting condition enhances weight loss. 8 healthy young men performed early morning slow cardio under 2 conditions:4
1. Empty stomach
2. After eating
Eating increased both oxygen consumption (VO2) and respiratory exchange ratio (RER) significantly, 12 hours after the cardio, VO2 was still higher for the group who had eaten, although RER was significantly lower in the FED test, indicating greater fat burn.
The group that ate before the moderate cardio session continued to burn significantly more calories up to 24 hours after the exercise bout. The authors concluded that “when moderate endurance exercise is done to lose body fat, fasting before exercise does not enhance lipid utilization (fat use); rather, physical activity after a light meal is advisable.”
While research and studies are still ongoing, there are a few certainties. Steady state fasted cardio might burn more fat during your workout, but your post-workout fat burn is compromised.
Who is right? The following will inform you of what research has to say about the topic and offer compelling reasons why fueled exercise leads to greater overall fat burn.
Cardio on an Empty Stomach Burns More Fat DURING Exercise
Two fuel sources—carbs & fats—are used to generate energy for muscle contraction during exercise. For endurance exercise performed at a moderate intensity, you obtain 50–60% of energy needed from glycogen (which is stored energy from carbs) and the rest from fats.
When you deplete glycogen stores by fasting overnight, or going several hours without refueling, fatty acids break down in the mitochondria to be used as a secondary energy source. As workout intensity increases, your reliance on carbohydrates increases as well.
In one study that tested the fat burning effect cardio on an empty stomach, six healthy men cycled for 60 minutes at a low to moderate intensity:1
Group 1-Fasted overnight before the bike ride.
Group 2- Performed the bike ride after ingesting 0.8g/kg of glucose or fructose to replenish glycogen levels 1 hour prior to the workout.
Results: After 20-30 minutes of exercise, the rate of fat burn was higher in the fasted group than in the glucose or fructose group. This trend continued throughout 50-60 minutes of exercise. There was also a higher quantity of FFAs (Free flowing fatty acids) available in the blood in a fasted state throughout the exercise.
The Take Away: This particular study suggests that more fat was burned by the group that performed MODERATE activity on an empty stomach… DURING THE EXERCISE ITSELF.
So Should You Perform Cardio on an Empty Stomach?
Research shows that people who burn fat during their workouts actually burn less fat the rest of the day.
Evidence supporting fueled exercise
Researchers from Italy investigated the contrasting reports on whether training in a fasting condition enhances weight loss. 8 healthy young men performed early morning slow cardio under 2 conditions:4
1. Empty stomach
2. After eating
Eating increased both oxygen consumption (VO2) and respiratory exchange ratio (RER) significantly, 12 hours after the cardio, VO2 was still higher for the group who had eaten, although RER was significantly lower in the FED test, indicating greater fat burn.
The group that ate before the moderate cardio session continued to burn significantly more calories up to 24 hours after the exercise bout. The authors concluded that “when moderate endurance exercise is done to lose body fat, fasting before exercise does not enhance lipid utilization (fat use); rather, physical activity after a light meal is advisable.”
While research and studies are still ongoing, there are a few certainties. Steady state fasted cardio might burn more fat during your workout, but your post-workout fat burn is compromised.
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