Does Performing Cardio on an Empty Stomach Burn More Fat?

Written by By Scott Charland MA, SCCC, CSCS Tuesday, 24 January 2012 21:35

Does Performing Cardio on an Empty Stomach Burn More Fat?

The idea of performing cardiovascular exercise on an empty stomach to burn more fat has existed for years. The notion seems plausible: with fewer carbohydrates to burn as fuel, the body turns to fat as the next available source of energy.

What does the best available research say?

A study in the February 2011 edition of Strength and Conditioning Journal found no meaningful difference in the amount of fat burned by participants during cardiovascular exercise in a “fasted state”—  on an empty stomach— as opposed to exercise following food consumption. What the study did find was that muscle loss as a result of exercising on an empty stomach was more likely with the body increasingly turning to protein stores for energy. Not surprisingly, exercise intensity and total calorie burn also diminished in trainers working on an empty stomach.4

Research aimed at promoting the efficacy of cardio performed in a fasted state overemphasizes the percentage of fat burned at the expense of total fat burned. For example, if you performed 20 minutes of cardio on an empty stomach and— to make the math easy— burned 300 calories with 200 of those calories coming from fat, 67 percent of your calories used would have come from fat. However, without any food in your system, your training would likely have been sluggish and low in intensity. Contrast that with a fully fueled, fully energized 20-minute cardio session where you burn 600 calories with 250 of those calories coming from fat, 42 percent. The fasted-state session burned a greater percentage of calories as fat, but the fully-fueled session actually burned more fat overall.5

What about high intensity cardio performed on an empty stomach? The risk of driving your body into a catabolic state where it begins to feed on protein and the very muscle you’ve spent months and years building to meet the high energy demand is far too great to offset any potential fat loss.

If jump-starting your day with low to moderate intensity fasted-state cardio helps you mentally prepare to climb the corporate ladder or if it’s the only time you can find to walk your dog, keep it up, you’re not doing any damage. There exists, however, no legitimate strength and conditioning or fitness professional who would ever advise regular high-intensity cardiovascular training or strenuous exercise of any kind on an empty stomach.