If the length of this article attacks your ADD, then feel free to start skipping paragraphs until you see "in summary." For the rest of you, I have to make the distinction that burning fat directly
is what we're assessing. Indirect burning of fat is a little too big of an issue. Indirect burning of fat being something along the lines of spending 6-8 weeks on a routine designated to increase leg muscle cross sectional area so that oxygen delivery to the legs at rest can gradually increase, by which this oxygen can go through the electron transport chain via the assistance of fat burning in the Kreb's cycle. Something like that. Something with several of steps that takes months to accomplish. We're not getting into that at all. We're concerned only with the direct burning of fat- how to make it happen as fast as humanly possible.
going to be a lot to set up for this, so we'll start from the top. There's a bunch of ways to produce energy for exercise, and each way is essentially designed to simply produce ATP, by which your body will break up the ATP to release that energy and use it for your exercise. Does that make sense? So basically you need ATP to perform any exercise, and your body can make it via several energy cycles.
First, there is free available ATP kind of just floating around. It has nothing to do with carbs, fat, or protein. It's just already ATP, energy that's ready to go- and is obviously therefore the fastest way for your body to produce energy. So naturally you use it first at the onset of any activity. And since it's readily available, the rate is not a limiting factor for power. The slower ATP production cycles cannot produce it at nearly the same rate that your body can potentially use it. So the free ATP has an advantage. The problem is that it's very limited. If you actually did have enough free ATP to complete a workout with, you'd probably weigh 1000lb. You'd be really strong, but it'd be ridiculous. I doubt you'd even be able to walk.
The other first call energy system is the creatine phosphate system. This also has pretty much nothing at all to do with carbs, fat, or protein, just energy in the form of ATP. And it produces it off the broken up parts of ATP pretty much as fast as just having it ready in the first place. But again, this is limited. It only lasts for a period of a few seconds. So you'll be really strong for a few seconds, then you'll move onto the next cycle.
Glycolysis is the next fastest energy cycle. Not as
fast by any means, but it's pretty quick. This is one of two cycles that does
deal with your carbs, fats, and proteins. But this is the anaerobic one. Anaerobic meaning "without oxygen." Using fat requires oxygen. So there's not much point in discussing this cycle except how to avoid it, which we'll get into.
The last energy cycle is oxidative phosphorylation, and it's the aerobic cycle, meaning "with oxygen." So naturally, this is the cycle you burn fat in. And it's a huge drawn out, slow cycle. It takes forever to get through the thing, but it's your best one. And the reason it takes forever is because there's actually a succession of two processes. Kreb's cycle first, which takes the calories mainly from your fat, and produces substances called NADH and FADH from them. So that's the "fat burning" part of the process, but you have no ATP yet, and you need ATP for energy, so you have to take those two things that end in H (ending in H is really all that matters- the H being hydrogen, hydrogen being what gives you your ATP, the rest of the substance is simply a hydrogen carrier molecule), so you take your NADH and FADH and send a pair of hydrogen molecules down the electron transport chain. Electron transport chain being the second process in the energy cycle. Now what happens here, is that there's a series of three different molecules in order which all like the hydrogen. So the hydrogen bonds with the first one, then breaks to bond with the second one which has a higher attraction, then breaks to bond with the third one because the third one has the highest attraction. And the third one is oxygen. So essentially here's your fat burning energy cycle: you burn fat to make hydrogen carriers, which transport the hydrogen to a group of molecules that have an attraction to it, send a pair of hydrogens down the chain, eventually bonding with oxygen, so you got H2O, i.e. water. And every time the hydrogen goes from one molecule to the next, you get an ATP out of it. So you've got the energy production and the fat burning.
But this cycle won't happen if you're short on breath because the required oxygen in the end of the chain comes from your breathing. Hence aerobic, "with oxygen." As soon as you're short on breath, it's back to glycolysis, "without oxygen." And being that oxidative phosphorylation is the only way your body can burn fat, this is the cycle you want to be using. So you can't be short on breath.
Those are the primary ways for your body to produce the energy to exercise. Keep in mind that all
energy cycles are always
working in your body continuously. The thing that changes is the composition. Whether 80% of your energy is coming from glycolysis, or 80% from oxidative phosphorylation depends on several factors- and it's not just breathing.
What you do for exercise, your hormone levels, your diet, and your exercise timing all come into play as influential factors.
As far as exercise goes, it's obvious now that only aerobic exercise will burn fat. Squats, pull-ups, sprinting, and abdominal work are not burning fat. Walking is burning fat. Biking is burning fat. Aerobic exercise is burning fat. This does not mean aerobics classes- those burn no fat either. We'll discuss this later. Point being, fat is a substrate for aerobic exercise, and that's it. Nothing else.
Now that you understand some of the parameters of exercising within oxidative phosphorylation, I'm going to add a couple more steps. My apologies. Okay, oxidative phosphorylation is the only way to use fat as energy. This you know. But using fat as energy implies using free fatty acids, and free fatty acids are only a part
of stored body fat. Stored body fat (adipose tissue) comes in the form of triglycerides. Triglycerides are composed of two different substances: a glycerol molecule, and 3 fatty acid chains. With me so far?
Okay, so of these two components, the glycerol is not a fat, rather an alcohol, of which the function is simply to hold the three fatty acid chains together to make it easier to store as one big unit. You cannot use an entire triglyceride in its storage form. Nor can you use glycerol in oxidative phosphorylation. So you're forced to separate the three fatty acids from the glycerol before you can use any of it. This separation is called lipolysis. Once lipolysis takes place, the fatty acids can be used in the Kreb's cycle to produce the NADH and FADH for the electron transport chain. This is how you use body fat as energy.
But adipose tissue is not the only type of fat available. This is why I bring this up. Triglycerides are also stored in the muscle, and free fatty acids are contained in the blood. And what you want
to burn the adipose tissue because that's the only one you can actually see. In order to do this, you need to modify your exercise to encourage it.
Eliminating the use of muscle triglycerides is fairly easy: don't workout too intensely. You have three types of fibers, fast twitch, medium, and slow twitch. The medium, type IIa, uses muscle triglycerides most. The fast twitch, type IIb, uses no fat, and the slow twitch, type I, uses predominantly adipose tissue and blood triglycerides. We'll talk about separating the use of adipose tissue and blood triglycerides later. In the mean time, use your slow fibers. How? Just like we've been talking about: find your aerobic pace.
And how do you judge this aerobic pace? "You should be able to talk comfortably." You've heard that before, yes? Okay, that's fine. Yes, you should be able to talk somewhat comfortably. Don't though. If you start talking, you're not breathing enough, and if you're not breathing enough, you don't have that oxygen at the end of the electron transport chain, and therefore you're not burning fat. So yes, you should be able to talk, and more important than that, don't take advantage of that ability.
Once you're at this aerobic pace, there are a couple considerations. The most important of these is the physiological steady state. You'll understand why in a couple minutes. I'll start off with this: have you ever noticed when you start something intense, you're not breathing like crazy right away? And then your breathing increases rapidly after a bit of a lag time? And then when you're done with the activity, you're still breathing really hard but you're not doing anything anymore, just breathing tons. There's a reason for that.
The reason you don't start breathing heavily right away is because you have a certain amount of oxygen already available. All day long you're breathing. I hope that's obvious. Daily life is basically a huge, really slow aerobic session. So you're constantly using oxidative phosphorylation- unless you feel really out of breath all the time, but if that's the case, wow, go see a doctor, don't just sit there reading my site. Anyway, you always have oxygen available. Any time you increase the intensity of what you're doing, the metabolic signals of that increase in intensity take a moment, followed by a lag for oxygen's delivery. So you drain the available oxygen, then the signal is sent to start breathing more. By the time that signal arrives, you're already out of oxygen, so your body is in full utilization of the anaerobic pathway. But you're going to stay
in the anaerobic cycle until the blood can transport a sufficient amount of oxygen from the lungs to the muscle cells that need it. And there's no point in breathing heavy before the signal arrives, because oxygen delivery works by concentration gradients, and you can't breathe on purpose to change that. If the concentration of oxygen is lower in the cells than in the blood, the cells take oxygen from the blood until it evens out. This lowers the blood's concentration, so it takes from the lungs until they're even. So the signal arrives to start breathing heavier when your blood oxygen concentration lowers, and continues to lower rapidly enough to justify rapid uptake from the lungs.
So essentially, it takes a period of time for the signal to arrive to breathe heavier, and then more time from there for the oxygen to arrive at the cells that need it. But you don't stop the activity when this happens, you keep going without really noticing. That's because you have glycolysis producing all your energy every time the intensity increases. Glycolysis being the anaerobic cycle that operates without the use of oxygen. And strictly on carbs. Then eventually when your oxygen can catch up, you can return to oxidative phosphorylation, and return to burning fat again.
So what is a steady state? Not having these increases in intensity which create an oxygen deficit and prevent you from burning fat. Every time you increase intensity, you can only burn carbohydrates. Nothing else until the metabolic signal and extra oxygen delivery are complete and your system can catch back up to the demand. So in these aerobics step-classes, every time you change your step pattern, you quit burning fat for a period of time. Then when you're about to return to oxidative phosphorylation, you change your step pattern again. Steady states. Use steady states. Your heart rate, breathing, pace, all of that, all of that should remain steady for long periods of time. Every time you increase your intensity, you interrupt fat burning.
That's not to say never
increase your intensity, we'll talk about that in just a minute. But the take home message so far, is that pacing yourself in a steady state of aerobic exercise is physiologically the only
way to burn fat.
And if you were wondering, the heavy breathing at the end of activity where you're doing nothing is the replenishing of free ATP and the creatine phosphate stores, and the muscle and blood oxygen stores. Plus your metabolic rate remains elevated due to your increased heart rate and breathing, which are both burning calories themselves, causing your breathing to be elevated further. I think it's kind of funny. You probably don't. That's fine. Some other detail stuff plays in too, but it's not that exciting. Lactic acid conversion, hormone release, etc.
As far as hormones are concerned, there are several by which their levels help determine which fuel source your body will prefer. Catecholamines (epinephrine and norepinephrine), insulin, and glucagon all deal with lipolysis. You remember lipolysis right? I.e. allowing triglycerides to be used by breaking them up into glycerol and free fatty acids? That one. Effectively, plasma insulin flat out blocks lipolysis, so you can only use blood triglycerides for fat use. This is bad. This means you burn no body fat whatsoever while exercising. The good news is that insulin is the only bad one. Epinephrine, norepinephrine, and glucagon all promote lipolysis. And
, insulin eventually promotes the release of glucagon. So There's much more in your favor hormonally than against. The problem is that it's easy to get insulin in your system, and harder to get the others.
Norepinephrine is released exponentially proportionate to intensity. So higher intensities cause higher norepinephrine. The problem with this is that if the intensity gets too high, you're not burning fat regardless of the presence of norepinephrine. The roll of intensity guiding the determination of energy cycles is a much more powerful determinant, but it does give you some incentive to increase the intensity somewhat. The incentive to hold an aerobic steady state at a slightly higher intensity.
Epinephrine is virtually the same thing as norepinephrine, but its release also comes with increased duration, encouraging that slightly higher aerobic steady state to be held for a bit longer. The longer you're in that state, the greater the progressive increase of epinephrine levels for more reliance on triglyceride sources all the while. Granted, if you up the intensity too much for the epinephrine, you increase the production of lactic acid, and once that happens you're inhibiting fat metabolism anyway. So a higher aerobic steady state within reason
should be held.
Then glucagon is simply a counter-hormone to insulin, released after insulin. So there's really no purpose to try to increase it. Be glad it's there, but that's about it. The only thing that really has an impact on it is your diet, but only because of direct insulin effects. Eat a carbohydrate. Insulin. Eat more carbohydrates. More insulin. See where I'm going? There's problems with eating before exercise. As soon as you eat, your body's releasing insulin, which can hang around in your system for a few hours interrupting your ability to perform lipolysis, and therefore your ability to burn any body fat. So if you are going to eat first, at least wait a couple hours afterwards to let the insulin drop down and the glucagon to be in the system. If you do this, the insulin that's left in your system can be diminished during the first 30 minutes of your exercise. After that it's usually low enough to not have to worry excessively. But do you see where this would make cardio below 30 minutes moderately unproductive? If at 30 minutes you're finally burning enough fat to make it worthwhile, why would you want to quit there? Other than that, if you eat a big meal, blood needs to go to your stomach to digest the food. You only have so much blood in your system. If tons of blood is going to your stomach to digest tons of food, you're obviously detracting blood from other areas. And this effect may be minimal, but consider that you do need blood flow to the adipose tissue in order to use any of it.
As far as the most effective time to perform this exercise, first thing in the morning. Wake up and go. You obviously haven't eaten in several hours, so insulin plays virtually no role at all, the catecholamines can be released, and you have a very low metabolic rate that should be remedied anyway if you want your body to burn more fat during the course of the day. But being as you've done nothing for hours, getting these processes up and running takes time. When you start using your muscles, their uptake of free fatty acids increases immediately, but lipolysis does not increase right away. So you're not burning much adipose tissue in the first 10 minutes or so. Instead, being as your pace will be appropriate to utilize fat, you'll use the free fatty acids in the blood. Although these could supply enough energy for you to use them at any pace in this phase, they won't. Bastards. They'll only give up about half their supply, so there's really no need to go fast during the first 10 minutes. You won't burn body fat and you don't have tons of free fatty acids in the blood to go through. But when lipolysis catches up to speed, you can use your adipose tissue at that point, so up the intensity and hold a moderate steady state for the rest of the session.
In summary, only aerobic exercise uses fat. Anaerobic does not. That said, cardio is really the only way to do it. This does not mean cardio classes. Those do nothing. It means, walking, biking, elliptical trainers, etc. If possible, you want to do this first thing in the morning, before you eat anything. Start relatively slow for the first 10 minutes, then increase the pace to a moderate intensity and hold that pace constant for as long as you can without dying of boredom. The longer the better, considering you gradually use more and more body fat as time progresses. If your cardio does not take place first thing in the morning, this 10 minute warm-up time should last only 2-3 minutes and try not to eat for a couple hours prior.
To judge intensity in the period following your warm-up, rely on the "can you talk comfortably" rule. But seriously please don't talk comfortably while you're exercising. Use it as a theory
. If you start talking, you interrupt your breathing, then you have to take the intensity down to be able to continue talking at the same physiological energy demand. Just don't talk, and while you aren't talking, think about what intensity you could
talk at if you needed to. Then hold that exact pace, speechless for the whole session. If you up the intensity, then lower it, then increase it again, you aren't burning fat. Short warm up, long steady-state phase, don't eat beforehand. That's it. Go become grossly lean.