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Cardio Before Breakfast—Debunked???

October 25, 2013

We’ve all heard it before, the theory that doing cardio on an empty stomach after an overnight fast sends fat burning into overdrive. If only it were that simple …

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.

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?

Not so fast. Notice how “moderate” exercise is emphasized in the example above?

Research shows that people who burn fat during their workouts actually burn less fat the rest of the day. Overtime, fat burning is not an immediate process, rather, it occurs over the course of, not a few hours, but a few days.. As you burn more carbohydrates during your workout, the body will burn more fat post exercise.

This “afterburn effect” where your metabolism is elevated for several hours or days following your workout is critical when debating the benefits of fasted cardio. While you may burn more fat during your workout on an empty stomach, your overall workout output will be lower and your body’s ability to burn fat post-exercise is compromised. Consider the whole 24 hour period and cardio on an empty stomach is less effective.

A good pre-workout rule of thumb is to consume approximately 1/4 gram of carbohydrate and 1/8 gram of protein per pound of your ideal bodyweight (which may differ from your actual weight).

For example, if your ideal bodyweight is 135 pounds, then your pre-workout meal should consist of approximately 30 grams of carbs and 15 grams of protein. A shake made of natural fruits or fruit juice and whey protein is a good option.

To accommodate time constraints if cardio is done early in the morning before breakfast, use powdered or encapsulated Branched Chain Amino Acids and a carbohydrate drink in the form of dextrose. Dextrose is a simple sugar. Gatorade is filled with 35 grams of simple carbs in the form of dextrose.