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Cardio on empty stomach? YES OR NO?



Aug 11, 2010
Let's take a look at the reasoning for doing cardio in the morning on an empty stomach...

1. Glycogen is depleted therefore more fat is burned - This is the major benefit people who push this method use to support their position. What they fail to realize is that anyone with weight training experience has (or should have) more muscle than is needed to sustain a healthy life. All of this extra muscle is detrimental to the survival of a human! Why? First of all, the individual body has one purpose in life. That purpose is survival. Fat is a much more efficient energy source for survival because it is not energy costly - it does not require calories to sustain. On top of this, fat is slower burning, as it is more calories dense. Therefore muscle will be burned before fat when in a state of starvation, as fat would keep you alive longer! That's the catch - just because glycogen stores are depleted that doesn't mean the body will just go straight to fat stores for its energy. How great that would be! Unfortunately, it's just not that simple. In the morning, glycogen is substantially depleted, in effect, so is ATP. If you have read some of my other articles you would know that ATP is the only source of energy for muscular contraction.

Heavy productive weight training depletes glycogen and ATP with each contraction. ATP is not only the fuel for muscular contraction, it also plays a large role in protein synthesis and repair itself. After weight training ATP and glycogen are depleted (heavy weight training uses the anaerobic glycolysis mechanism on ATP production),and time is needed for glycogen stores to replenish. Glycogen replenishment can take up to 3 days to complete! If you deplete more glycogen than is necessary you are putting your body through unnecessary stress, which will inhibit your bodies ability to build muscle! Less ATP means less energy for proteins synthesis. It's apparent that you want to stimulate as much muscle growth as possible, with the smallest amount of glycogen and ATP depletion, which means that you should train as little as possible, while still achieving the desired results.

So how does this matter in this situation? Cardio in the morning on an empty stomach means cardio with little glycogen, and thus little ATP. Remember that cardiovascular work requires muscle fibers to contract. Just because an activity is aerobic doesn't mean it does not require muscle fibers to perform the work. The primary source of contraction during aerobic work is the Type I muscle fibers. They are called upon during aerobic work because they have a long fatigue threshold meaning - they can maintain contraction for long periods of time. Type I fibers use the oxidative phosphorylation (Kreb's cycle and electron transport) - an aerobic mechanism for energy production. This is the method of energy production in which the body metabolizes carbohydrates and fats to produce energy. The body may also use protein when carbohydrate and/or fat energy are not available through a process called gluconeogenesis. Carbs are used primarily for this, and consequently in aerobic work. This method of energy production produces, bar far, the most amount of energy. You can literally keep going forever until you pass out with this energy system. The reason for this is because the body will catabolize itself in order to meet energy demands. You guessed it - IT WILL BREAK DOWN MUSCLE TISSUE FOR ENERGY. Don't get me wrong here, the body will also break down fat for energy. I'm sure you have been taught in high school biology that fat is the preferred energy source during aerobic exercise. This is completely true for those who do not have any "excess" muscle sitting on their bones. You see, when we weight train we create an environment in which the body is forced to synthesize new proteins in order to protect itself from future stress. This is a basic principle in weight training - super compensation and overload. Overload is the means in inducing progressive super compensation. The body will not synthesize protein it doesn't need. This matters because during aerobic exercise the body has three choices in going about meeting the energy requirements. It can...

1. Use stored glycogen.

2. Use stored fat.

3. Use stored amino acids (muscle).

When we do cardio in the morning on an empty stomach we pretty much eliminate option one. Muscle glycogen stores can never be 100% depleted, if they were we wouldn't be able to move. But, there are three places where glycogen can be found in the body (remember - we don't actually eat glycogen). The first place is in the liver, the second place is in the muscles, and the third place is in the blood stream. In the morning, after your 6-10 hours with no energy (food) liver glycogen will be just about depleted, blood glycogen will have been burned for energy, and muscle glycogen will have been severely depleted. What this means is that your body is in a state of extreme catabolism, it is literally breaking down muscle at an alarming rate. This is because when the liver runs out of glycogen it takes alanine, arginine and the other substrates, from the muscles in order to make more. This is muscle breakdown (atrophy). After waking up, you start to do activities (yes, going to the bathroom and watching TV is an "activity"). What this means is that you are increasing the bodies immediate energy requirement, which means - more muscle being broken down to meet energy needs. Then, the worst thing you can do at this time is to introduce aerobic activity. This means another increase in energy requirement, and further increase in muscle catabolism. Not a good situation to put your body in. Simply having a light meal before this activity would prevent all of this. The body would be taken out of its extremely catabolic state, it would have immediate energy other than muscle to use as fuel, and you will also have more energy to do your cardio with. More effort going into your cardio equals more benefits coming out of it.

2. Increased metabolism for the rest of the day - This one is completely sensible. The thing is - the amount of food and the amount or glycogen you posses have no effect on this. Cardio in the morning is NOT a bad thing; cardio in the morning on an empty stomach is the bad thing. The solution to muscle catabolism? Eat before your cardio.


Dec 12, 2010
Yes I try as much as I can to do it on an empty stomach but usually never in the morning and when I say empty I mean I drink a protein shake before I go so it is not totally empty just not full.


TID VIP Lady Member
May 1, 2012
i do it without eating anything. As long as i'm on an AS i'm GTG. but im doing low steady cardio , walking , bike


VIP Member
Nov 1, 2010
I do cardio both with food and not...lose most BF on empty stomach though...


Jun 6, 2012
Try doing it with a kebab in one hand and a energy drink on the other


Sep 10, 2012
I think as an assisted athlete it's probably the best type of fat burning you can do (on an empty stomach) - However, for somebody natty I think you have to be very careful as to when you do cardio, and how much as it's a very fine line between burning fat and eating away at hard-gained muscle.


TID Board Of Directors
Jan 18, 2011
supposedly it's somewhat of a myth that you burn more fat per se.... while you will burn more fat/glycogen stores depleted, you will store more fat during the day to make up for it...Logically speaking i think the way to mitigate this problem is with a CKD diet, where your refeed day has no cardio or exercise..... the depletion phase will allow a 2-2.5 x update in glycogen from carbohydrates during refeed, and as long as ketosis can be achieved rather quickly, during the trace carb days, your body will constantly be burning fats for energy.... even if it isn't fully "keto-adapted" long as you test even in the low end of ketones present in your urine with a keto stick I think you will continue to lypolize more adipose tissue throughout the day, as opposed to building stores. Somebody correct me if I am wrong!!!!!! Especially if you are eating quality fats from eggs, fish, red meat, peanut butter, flax and Omegas.... you can even be eating 25% more fats than you typically would and still see exellent results while minimizing cravings.

The above point is valid, however it fails to indicate that nutrient absorbtion (protein, carbohydrates, fiber) happens not only in the stomach subsequent to a feeding but it also occurs in the small intestine... this can occur for many hours (30+) before the food has been categorized as waste and excreeted... Your body isn't starving... your body is feeding long after you eat..... I will site intermittant fasters now, who can maintain muscular physiques and a decent amount of muscle mass, with long fast periods and small feeding windows.....cardio outside of the feeding window is fine because the body is still 'feeding.' 8 hours after your last protein rich meal, and you are still breaking down and absorbing nutrients... all the while they are becoming bioavailable in the blood stream, and carried to cells.
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TID Board Of Directors
Sep 30, 2011
Doesn't really matter it is the calories that matter the most.


Aug 2, 2013
I've heard both sides on this topic so I don't really know which is broscience or fact. Personally, I do my cardio when I first wake up, and always on an empty stomach. However I do it this way bc it tends to wake me up and make me more focused during my work day. Currently I'm on a clean bulk so I only do cardio on my days off, but I do like to do body weight stuff every morning and it seems to have the same effect (not the fat burning but the wake up/focus). If I'm on a cut it works like a charm for BF loss.


TID's Official Donut Tester
Oct 14, 2012
I've also heard both ways, but I don't think it matters too much.

Bottom line, as long as you do your cardio, I don't think it matters which time or when you do it. As long as you do it.

When I did my last cut I did cardio on an empty stomach when I first woke up. It worked

When I was bulking, I was doing cardio in the evening (HIIT) after I had eaten all day. It worked also.

I think whatever you prefer.

Just my .02


VIP Member
Oct 25, 2011
Calories burned during cardio mean nothing. It doesn't do shit for you. You burn fat while at rest. That being said I generally do fasted cardio because the body will release GH when doing fasted cardio to keep you from going hypoglycemic. I do HIIT cardio for about 16min and then another 4min to bring my total to 20min. I generally don't ever go beyond that unless I'm doing something like hiking with a pack or some other activity which I don't do for cardio I do for fun.