Let’s pretend for a second you’re going to drive from Ann Arbor to Chicago. You hop in your car, turn on the ignition, and the gas gauge shoots to E. You smile, say, “perfect!” and jump on the expressway thinking it will be great for your car to take this trip without any fuel. You’d probably think that’s crazy – right? Well, it’s just as crazy as exercising on an empty stomach in hopes to burn more body fat.
I’m sure you’ve no doubt heard of the myth, ‘to lose body fat faster, you should exercise in a fasted state.’ People believe that it taps into your fat stores faster. I mean, makes sense, right? If carbs aren’t readily available, like when you’ve fasted all night long, you have to burn fat – what else is there? Well, there’s fuel you don’t want to burn (like muscle).
Let’s look quickly at 3 reasons not to do cardio on an empty stomach:
1) You burn muscle tissue NOT fat.
At the intensity that nearly everyone exercises at (> 50-60% of maximum heart, or call it above 110 bpm) the predominant fuel source burned for energy is carbohydrate. If carbs aren’t readily available, your body has to turn to muscle tissue as a fuel source, since it’s the only fast-acting fuel available. True, fat is a fuel source, but it takes a very long time to be broken down into energy. As a result, unless exercise intensity is slowed to a crawl (like walking on a treadmill at 1.7 mph) you will burn muscle, not fat, which is very counterproductive.
2) You will burn fewer calories.
That’s right, not only does this result in less fat loss because you’re burning muscle tissue, but it results in lower intensity exercise (because your body is trying in vain, to reduce your exercise intensity, so you don’t burn muscle tissue). Keep in mind that the whole process of fat loss is to create a calorie deficit, by exercising in a fasted state it greatly diminishes your ability to create a significant calorie deficit.
3) You could get sick, throw-up, or pass out.
Any or all of these three can occur because of low blood sugar, which you will almost certainly cause VERY quickly when exercising in a fasted state. Exercise is hard enough for most people without puking or passing out while jogging on a treadmill. Why anyone would intentionally put themselves in a position to do so is beyond me.
Take Home Message:
If you’re looking to get more out of your cardio (from a fitness and a fat loss standpoint) try consuming a little bit of protein and carb before exercise. This process of nutrient timing will diminish muscle breakdown, aid in fat metabolism, speed up recovery, and result in more calories burned. In short – stop at the gas station before jumping on the freeway!
About the Author:
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Michael Stack is the founder & CEO of Applied Fitness Solutions and Frontline Fitness Pros. He is a faculty lecturer for the University of Michigan’s School of Kinesiology. He is also the creator and the host of the Wellness Paradox Podcast, produced in conjunction with University of Michigan.
Michael is an exercise physiologist by training and a health entrepreneur, health educator, and fitness industry advocate by trade. He is dedicated to enhancing the standard of practice of, and advocating for, fitness and wellness professionals to ensure they become an essential constituent in the healthcare delivery system.
With a career spanning over three decades in fitness, health, and wellness Michael has a deep knowledge of exercise physiology, health/wellness coaching, lifestyle interventions to mitigate chronic disease and leadership. He is credentialed through the American College of Sports Medicine (ACSM) as an Exercise Physiologist (ACSM-EP), Exercise is Medicine practitioner (ASCM-EIM), and a Physical Activity in Public Health Specialist (ACSM-PAPHS). Michael is a National Strength & Conditioning Association (NSCA) Certified Strength & Conditioning Specialist (CSCS), and a CDC Diabetes Prevention Program (DPP) Lifestyle Coach.
Michael received his undergraduate degree from the University of Michigan’s School of Kinesiology in 2004 and is currently a Master’s of Public Health (MPH) candidate at University of Michigan, with a specific concentration in health behavior and health education.
Michael is a board of directors’ member for the Physical Activity Alliance and Michigan Fitness Clubs Association. He sits on the University of Michigan’s School of Kinesiology Alumni Board of Governors. Michael is an expert curriculum reviewer for the American College of Lifestyle Medicine. Finally, he is a member of the executive leadership team for American Heart Association’s Heart Walk.
Michael lectures nationally for several health/fitness certification and continuing educations, including; IHRSA, the Medical Fitness Association, the National Strength & Conditioning Association, and SCW Fitness.