It’s 6 am. You blindly reach for the alarm clock as your eyes slowly flutter open. It’s time for fasted cardio.
For two weeks straight, you have performed fasted cardio with alacrity knowing your burning the most fat — at least that’s what a bodybuilder at your local gym told you.
But on this particular morning, you begin to contemplate whether your fasted cardio regimen is superior to other forms of cardio for burning fat.
Fasted cardio is typically performed immediately upon rising on an empty stomach. It’s a popular fat burning strategy employed by bodybuilders and physique athletes.
The theory behind this strategy is that by performing cardio after an overnight fast, stored body fat is preferentially burned for fuel.
Several studies support this contention showing that the ingestion of carbohydrates (e.g. breakfast), before cardio reduces fat oxidation. (1, 2) These studies also show that a higher percentage of calories as fat are burned with fasted cardio.
But the primary question is whether acute increases in fat oxidation during fasted cardio translate to a greater loss of fat over time compared to non-fasted cardio.
Fasted Cardio for Burning Fat
Research comparing fasted and non-fasted cardio programs find no differences in fat loss.
In one study, researchers took 20 young females and had them do one hour of fasted or non-fasted cardio, three days per week for four weeks. The researchers found no significant differences in fat loss between the two groups.
Another 6-week study showed no differences in fat loss between fasted versus fed interval training.
Fasted cardio does, however, burn more fat for fuel during exercise compared to fed cardio.
But it’s not the type of fuel used during exercise that’s important for fat loss; rather, it’s the energy deficit created on a consistent basis.
An energy deficit is created by expending more calories than you burn. This is accomplished by eating less than your daily energy needs or expending more energy than you’re taking in, or both.
Fasted cardio, however, does not enhance the number of calories you burn during the day.
This is because the human body is dynamic and continually adjusts its use of fat for fuel. Generally, if you burn more carbohydrates during cardio, you burn more fat during the day and vice versa.
Adherence Trumps Optimal
Dragging yourself out of bed an hour early to perform fasted cardio in hopes of a quicker six-pack is hardly worth it.
At best, the overall effect on fat loss associated with fasted cardio will be no better than performing cardio after consuming a meal. And it may produce inferior results.
Training on an empty stomach can make it difficult to sustain exercise at even a moderate level of intensity; forget about high-intensity interval training.
Research shows that a pre-workout meal allows you to train harder compared with fasting which can lead to more calories burned overall.
Therefore, do what you prefer.
If fasted cardio appeals to you, stick with that; if you prefer to have something in your stomach before a workout, do that.
But keep in mind, cardio — fasted or fed — itself isn’t enough to help you reach your fat loss goals. Changes in diet contribute more weight loss than exercise.
Start with your diet and incorporate your preference of cardio — preferable with some resistance training — for optimal results.