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A.M. Fat Burn
(As seen in IRONMAN Magazine)
By Tom Venuto, NSCA-CPT, CSCS

Does morning cardio burn more fat???Even though morning cardio has been embraced by bodybuilders as a "tried and true" fat loss technique, there is definitely not a unanimous agreement about its effectiveness, especially in the scientific community. Most competitive bodybuilders are die-hard advocates of doing cardio first thing in the morning before eating their first meal. They believe it will cause them to mobilize more stored body fat and increase their metabolic rate all day long.

Thereís quite a bit of scientific literature supporting the a.m. fasted cardio theory, but generally, the exercise physiologists and scientists tend not to buy it. They subscribe to the energy balance hypothesis, which states; as long as you burn more calories than you consume in each 24 hour period, then the time of day you burn them doesnít matter, nor does whether you burn them from fat or carbohydrate.

If you have even the most rudimentary understanding of human physiology and physics, you have to concede that the timing of your cardio is not the most important factor in fat loss. When you do your cardio wonít make or break you. Simply doing it whenever itís convenient and following a mildly calorie restricted diet is whatís important. However, thereís a very strong case for doing fasted a.m. cardio and if you want to gain every legal and ethical advantage possible in your quest to get leaner then itís definitely something you should take a closer look at and experiment with.

The argument in favor of fasted early morning cardio goes something like this:

1. When you wake up in the morning after an overnight 8-12 hour fast, your bodyís stores of glycogen are somewhat depleted (especially if you are on a reduced carb diet and you cut back on carbs late in the day). Doing cardio in this state causes your body to mobilize more fat because of the unavailability of glycogen.

2. Eating causes a release of insulin. Insulin interferes with the mobilization of body fat. Less insulin is present in the morning; therefore, more body fat is burned when cardio is done in the morning.

3. There is less carbohydrate (glucose) "floating around" in the bloodstream when you wake up after an overnight fast. With less glucose available, you will burn more fat.

4. If you eat immediately before a workout, you have to burn off what you just ate first before tapping into stored body fat (and insulin is elevated after a meal.)

5. When you do cardio in the morning, your metabolism stays elevated for a period of time after the workout is over. If you do cardio in the evening, you burn calories during the session so you definitely benefit from it, but you fail to take advantage of the "afterburn" effect because your metabolic rate drops dramatically as soon as you go to sleep.

Research supports this theory. A study performed at Kansas State University and published in Medicine and Science in Sports and Exercise showed that a kilogram of fat is burned sooner when exercise is done in the fasted state in the morning than when itís done later in the day. The researchers measured respiratory gas exchange, caloric expenditure and carbohydrate and fatty acid metabolism, and found that the amount of fat burned during aerobic exercise amounted to 67% of the total energy expenditure in the morning after a 12 hour fast. This is substantially higher than the 50% expenditure achieved when the same exercise was done later in the day or after eating.

A similar study from The Journal of Applied Physiology looked at the effects of aerobic exercise on lipid oxidation in fed versus fasted states. The researchers concluded, "our results support the hypothesis that endurance training enhances lipid oxidation in men after a 12 hour overnight fast." Yet another scientific paper, Optimizing Exercise for Fat Loss," reports, "The ability of exercise to selectively promote fat oxidation should be optimized if exercise is done during morning fasted metabolism."

Despite the fact that increased fat burning from morning cardio seems logical and is backed by research, the majority of scientists and exercise physiologists vehemently deny its effectiveness. They are quick to point out that you can find a study to support almost any theory you want to advocate. Interestingly though, even the most dyed in the wool academics agree that youíll burn more fat in the fuel mix as compared to sugars. The real controversy lies in whether this fact has any impact on overall fat loss in the long run.

Exercise Physiologist Greg Landry, MS, author of "The Metabolism System for Weight Loss and Fitness," explains, "I agree that you burn a fuel mix that is a little higher in fat if youíre exercising on an empty stomach. However, I think the real question is, does that matter? I believe we have a Ďpoolí of calories stored in different forms in the body (fat, glycogen, etc.), so Ďburnedí calories all come from the same pool. Thus, it really doesnít matter that the fuel mix has a little more fat in it at a given time. If itís pulling from fat stores at that time, then itís pulling less from glycogen stores and thus future consumed calories will be a little more likely to be stored as fat because glycogen stores are a little fuller. So itís all a wash."

Lyle McDonald, an expert on bodybuilding nutrition and author of "The Ketogenic Diet," agrees. He argues that the body will compensate later in the day and is simply "too smart" for strategies like this to make a substantial difference in results: "All that research says is that you burn a greater proportion of fat this way, which I agree with 100%," says Lyle. "The majority of research shows that as far as real world fat loss goes, it doesnít really matter what you burn. Rather, 24-hour calorie balance is what matters. Because if you burn glucose during exercise, you tend to burn more fat the rest of the day. If you burn fat during exercise, you burn more glucose during the day. The end result is identical. If that werenít the case, then athletes like sprinters who never Ďburn fatí during exercise wouldnít be shredded. Basically, they burn so many calories that they remain in balance and donít gain any fat. So, while morning cardio probably provides some psychological benefits to bodybuilders who are programmed to do it that way, I canít say that I think it will result in greater Ďreal worldí fat loss, which is what matters."

When it comes to "real world" fat loss, few people have more experience than Chris Aceto. A successful bodybuilder and nutritionist to some of the top pro bodybuilders in the world, Aceto is a firm believer in morning cardio. He unequivocally states, "The fastest way to tap stored body fat is to do cardio first thing in the morning on an empty stomach."

Aceto believes that looking at calories only in terms of energy in vs. energy out is "limited thinking." He asserts that there are more factors involved in "real world" results than just energy balance. This all comes back to the old argument, are all calories created equal? "Absolutely not!" Aceto declares. "A calorie is not just a calorie and exercise physiologists Ďfreak outí when they hear this."

"These guys are working from the assumption that itís just a matter of calories in vs. calories out, period," Chris continued. "With that line of reasoning, theyíd be forced to say that if I consume nothing but candy bars and Coca-Cola, and take in 100 calories less than maintenance, Iíd lose weight. We know itís not that simple. You also have to account for ratios of carbs, protein, and fat. Then thereís meal frequency too: From real world results we know you put down more muscle mass from 5 or 6 meals a day than from 3 meals a day. There are more things involved than just calories."

Whether or not morning cardio in the fasted state increases "real world" fat loss is still the subject of controversy, but there are many other reasons you might want to consider making it a part of your daily routine. Landry, despite his doubts about whether the fuel source matters, admits, "If I had to pick a single factor I thought was most important in a successful weight loss program, it would have to be to exercise first thing in the morning."

Here are some of the additional benefits of doing cardio early in the morning (whether fasted or not):

1.It makes you feel great all day by releasing mood-enhancing endorphins.

2. It "energizes" you and "wakes you up."

3. It may help regulate your appetite for the rest of the day.

4. Your bodyís circadian rhythm adjusts to your morning routine, making it easier to wake up at the same time every day.

5. Youíll be less likely to "blow off" your workout when itís out of the way early (like when youíre exhausted after work or when friends ask you to join them at the pub for happy hour).

6. You can always "make time" for exercise by setting your alarm earlier in the morning.

7. It increases your metabolic rate for hours after the session is over.

Of all these benefits, the post-exercise increase in your metabolic rate is one of the most talked about. Scientists call this "afterburn" effect the "excess post-exercise oxygen consumption" or EPOC for short.

Looking only at the number of calories and the type of calories burned during the session doesnít give you the full picture. You also need to look at the increased number of calories you continue to burn after the workout is over. Thatís right - work out in the morning and you burn calories all day long. Imagine burning extra fat as you sit at your desk at work! Thatís the good news. The bad news is, the degree of EPOC is not as great as most people think. Itís a myth that your metabolism stays elevated for 24 hours after a regular aerobic workout. That only happens after extremely intense and/or prolonged exercise such as running a marathon.

After low intensity exercise, the magnitude of the EPOC is so small that its impact on fat loss is negligible. Somewhere between 9 and 30 extra calories are burned after exercise at an intensity of less than 60-65% of maximal heart rate. In other words, a casual stroll on the treadmill burns some calories and provides other health benefits, but will do next to nothing to increase your metabolism after the workout is over via the EPOC mechanism.

EPOC increase with the intensity (and duration) of the exercise. According to Wilmore and Costill in "Physiology of Sport and Exercise," the EPOC after moderate exercise (75-80%) will amount to approximately .25 kcal/min or 15 kcal/hour. This would provide an additional expenditure of 75 kcal that would not normally be calculated in the total energy expended for that activity. An extra 75 calories is definitely nothing Earth shattering. However, it does add up over time. In a year that would mean (in theory) you would burn an extra 5.2 lbs of fat from the additional calories expended after the workout.

One way to get a significant post exercise "afterburn" is by using more intense cardio workouts such as high intensity interval training (HIIT). HIIT is done by alternating brief periods of high intensity work (85% or more) with brief periods of lower intensity work. Studies on the effects of HIIT have demonstrated a much higher EPOC, which can add substantially to the dayís calorie expenditure. In one study, scientists from the University of Alabama compared the effects of two exercise protocols on 24-hour energy expenditure. The first group cycled for 60 minutes at a moderate intensity. The second group performed HIIT, cycling for two minutes at high intensity followed by two minutes at a low intensity. The group that performed the HIIT burned 160 more calories in 24 hours than the low intensity group. That means the HIIT group would burn an extra 11.8 pounds of fat in one year if they did HIIT five days a week instead of conventional training.

Ironically, weight training has a much higher magnitude of EPOC than aerobic training. Studies have shown increases in metabolic rate of as much as 4-7% over a 24-hour period from resistance training. Yes - that means bodybuilding does burn fat Ė albeit through an indirect mechanism. For someone with an expenditure of 2500 calories per day, that could add up to 100 - 175 extra calories burned after your weight training workout is over. The lesson is simple: Anyone interested in losing body fat who is not lifting weights should first take up a regimen of bodybuilding. Worrying about details such as whether to do cardio fasted or fed is pointless if you're not even taking advantage of the major body-composition improving benefits of weight training!

A common concern about doing cardio in the fasted state, especially if itís done with high intensity, is the possibility of losing muscle. After an overnight fast, glycogen, blood glucose and insulin are all low. As weíve already concluded, this is an optimum environment for burning fat. Unfortunately, it may also be an optimum environment for burning muscle because carbohydrate fuel sources are low and levels of the catabolic stress hormone cortisol are high. It sounds like morning cardio might be a double-edged sword, but there are ways to avert muscle loss.

All aerobic exercise will have some effect on building muscle, but as long as you donít overdo it, you shouldnít worry about losing muscle. It's a fact that muscle proteins are broken down and used for energy during aerobic exercise. But you are constantly breaking down and re-building muscle tissue anyway. This process is called "protein turnover" and itís a daily fact of life. Your goal is to tip the scales slightly in favor of increasing the anabolic side and reducing the catabolic side just enough so you stay anabolic and you gain or at least maintain muscle.

How do you build up more muscle than you break down? First, avoid excessive cardio. Aceto suggests limiting your cardio on an empty stomach to 30 minutes, and then it would be "highly unlikely that amino acids will be burned as fuel." He also mentions that "a strong cup of coffee should facilitate a shifting to burn more fat and less glycogen. If you can spare glycogen, youíll ultimately spare protein too."

Second, give your body the proper nutritional support. Losing muscle probably has more to do with inadequate nutrition than with excessive aerobics. Provide yourself with the proper nutritional support for the rest of the day, including adequate meal frequency, protein, carbohydrates and total calories, and itís not as likely that there will be a net loss of muscle tissue over each 24-hour period.

Third, keep training with relatively heavy weights, even during a fat loss phase. Using light weights and higher reps thinking that it will help you get more "cut" is a mistake: What put the muscle on in the first place is likely to help you keep it there.

Still petrified of losing your hard-earned muscle, but youíd like to take advantage of the fat-burning and metabolism-boosting effects of morning cardio? One strategy many bodybuilders use is to drink a protein shake or eat a protein only meal 30 minutes or so prior to the morning session. The protein without the carbs will minimize the insulin response and allow you to mobilize fat while providing amino acids to prevent muscle breakdown.

In conclusion, it seems that A.M. cardio has enough indisputable benefits to motivate most people to set their alarms early. But letís talk bottom line results here: Does doing morning cardio in a fasted state really result in more "real world fat loss" than cardio performed at other times of the day or after eating? I have to believe it does. Common sense, research and experience from 28 bodybuilding competions all tell me so. Nevertheless, this will obviously continue to be an area of much debate, and clearly, more research is needed. In the meantime, while the scientists are busy in their labs measuring respiratory exchange ratios, caloric expenditures and rates of substrate utilization, Iím going to keep waking up at 6:00 AM every morning to get on my Stairmaster for some (pretty intense) cardio.


1. Aceto, Chris. Everything you need to know about fat loss. Club Creavalle, Inc. (1997).

2. Bahr, R. Excess post-exercise oxygen consumption Ė Magnitude, Mechanisms and Practical Implications. Acta Physiol Scand. Suppl. (1992) 605. 1-70.

3. Bergman, BC, Brooks, GA. Respiratory gas-exchange ratios during graded exercise in fed and fasted trained and untrained men. Journal of Applied Physiology. (1999) 86: 2.

4. Brehm, B.A., and Gutin, B. Recovery energy expenditure for steady state exercise in runners and non-exercisers. Medicine and Science in Sports and Exercise. (1986) 18: 205,

5. Brybner, BW. The effects of exercise intensity on body composition, weight loss, and dietary composition in women. Journal of American College of Nutrition, (1997) 16: 68-73

6. Landry, Greg. The Metabolism System for Weight Loss. Greg Landry. (2000).

7. Maehlum, S., etc al. Magnitude and duration of post exercise oxygen consumption in healthy young subjects. Metabolism (1986) 35 (5): 425-429.

8. McCarty, MF. Optimizing Exercise for Fat Loss. Medical Hypothesis. (1995) 44: 325-330

9. McDonald, Lyle. The Ketogenic Diet. Morris Publishing, (1998).

10. Melby, C. et al. Effect of acute resistance exercise on post exercise energy expenditure and resting metabolic rate. J Applied Physiology, (1993). 75: 1847-1853

11. Wilmore, Jack, Costill, David. Physiology of Sport and Exercise. (1999) 2nd ed. Human Kinetics

12. Tremblay, A, et al, Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism (1994) 43: 818-818

13. Treuth, M.S., Hunter, G.R., & Williams, M. Effects of exercise intensity on 24-h energy expenditure and substrate oxidation. Medicine and Science in Sports & Exercise. (1996) 28, 1138-1143

14.Wilcox, Harford & Wedel. Medicine and Science in Sports & Exercise, (1985) 17:2

Tom Venuto is a lifetime natural bodybuilder, an NSCA-certified personal trainer, certified strength & conditioning specialist (CSCS), and author of the #1 best selling diet e-book, Burn The Fat, Feed The Muscle. Tom teaches you how to lose fat without drugs or supplements using the little-known secrets of the world's best bodybuilders and fitness models. Learn how to get rid of stubborn fat and turbo-charge your metabolism by visiting, home of Burn The Fat, Feed The Muscle and www.BurnTheFatInnerCircle.Com, the Internet's premiere members-only fat loss support community. .

Copyright, Tom & Fitness Renaissance, LLC. This article was an exclusive for IRONMAN Magazine. No reproduction or this article is permitted without written permission.

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