Ep. #783: What Is the “Fat-Burning Zone” and Does It Matter?

Howdy. Welcome to Most for life. I’m Mike Matthews. Thank you for joining me today. And if you like what I’m doing here, please do subscribe to the show in whatever app you’re using because it helps boost the rankings of it so other people find it more easily, and it makes sure that you get notified when I publish new episodes, so you never miss a vital installment of Muscle for Life.

All right. In today’s episode, we’re gonna be talking about the fat burning zone. Something I’m sure you’ve heard about many times. I know I have. Going all the way back to the beginning of my foray into fitness when I was 17, 18 years old. I remember reading in the body building magazines, how if you’re gonna do cardio to get lean and you have to do cardio to get lean, of course, then you need to be doing it in the fat burning zone.

If you are not in the fat burning zone, then your cardio is going to be a lot less effective for losing fat or might be completely ineffective. It might only burn the glycogen in your muscles, for example. Or it might only burn carbohydrates in your blood from the food that you ate. Common claims right.

Now this idea has had impressive longevity. It has been around for at least 50 years now, and in that time many other workout trends have come and gone, and some do make comebacks because of the cyclical nature of things, but the fat burning zone. Idea myth as you’re about to learn has remained pretty steady, pretty constant in regular circulation.

Again, for several decades, people still think. That’s the ticket. That’s how you get lean. And yes, this is largely a myth, at least the way that most people understand it. And what that means then is if you’re doing all of your cardio workouts in a low to moderate intensity, yes, you can lose fat with that, but that is not necessarily better.

For losing fat than doing higher intensity cardio. And again, as you’re gonna learn in this episode, the higher intensity cardio is strictly speaking, more time efficient for losing fat because you’re gonna lose more fat in a shorter amount of time. But that doesn’t mean that you have to do a bunch of high intensity cardio either.

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And the idea is by working mostly in this zone, which is related to your heart rate, and I’ll get into that in a second, you are going to mostly lose fat in your workouts, and that is going to result in more fat loss over time than doing cardio in. A different zone in a carbohydrate burning zone, For example, a higher intensity zone.

Now, this is also referred to as the fat burning heart rate zone because the intensity of the training is often expressed as a percentage of your maximum. Heart rate. So this is where it takes a technical term and it has a scientific flare about it. Now, in order to understand how this idea came about, you have to understand how your metabolism works when you exercise.

So when you’re training, your body is using several different sources of energy. To power your workout and to stay alive. And the main ones are carbohydrate in fat. Now it uses different physiological processes, and these are known as energy systems to transform carbs and fats into usable energy for your cells.

Cause your cells can’t use molecules of carbohydrate or dietary fat. They have to be broken down. Into smaller things that your cells can use. Now when you are at rest, when your heart rate is low, your body is getting almost all of its energy from fat, and that is a very efficient, and it’s a very plentiful fuel source.

It is very easy to transform body fat into usable energy at a cellular level. Now at rest, of course, you’re not burning many calories. It doesn’t cost much energy to just sit there and as body fat is pretty energy dense, a pound of body fat contains about 3,500 calories. And to put that in perspective, I’m 193 pounds and I’m a lot more muscular than the average person.

So my 193 pounds costs more energy. To use and to maintain. Then someone else who weighs 193 pounds, but who has a lot less muscle. And Monday through Friday, I’m in the gym lifting weights for about an hour per day, and I do about 30 minutes of low intensity or low slash moderate ish intensity cardio. I hop on an upright bike and I usually make or take work phone calls during that time.

And then on the weekends, Saturday and Sunday, I usually do just the cardio 30 minutes or so and to maintain my weight. So my maintenance calories are around 3000 to maybe 3,200 per day. And so one pound of body fat has over an entire day’s worth of energy for me going into the gym, doing my cardio.

Otherwise, I’m not very active. I’m just sitting on. Computer typing or recording podcasts. But on the whole, if you look at my activity level, it is pretty good because I’m exercising 12 to 13 hours per week, and I’m fairly lean. I’m around probably 9% body fat, maybe 10%. So let’s just say I have 20 pounds of fat.

That’s what I’m carrying around. That’s probably about a. Worth of energy at my current activity level, meaning I could survive off of just my body fat for probably about a month, no food. So anyway, my point with all of that is body fat is very energy dense and it’s very easy to turn into cellular energy.

So that is the first resort of our body. Whenever it needs energy for anything, if it doesn’t have energy available from food that we just ate or ate some time ago, that it is still digesting. Absorbing. All right, so let’s come back to this point of us being at rest and our body getting most of the energy it needs from body fat.

Again, assuming that it can’t get in, get the energy it needs from food that we ate because it’s already done processing it. You can. Burn more energy, of course by moving around and you can move around more intensely to burn even more energy. But there is a side effect here. Yes, fat burning goes up.

However, the energy system that burns fat for energy isn’t able to keep up with the demand for energy, and particularly from your muscles as you are. Lifting weights or doing cardio or playing a sport or whatever. And so then what happens is the body starts to metabolize more and more carbohydrate. That energy system kicks in to pick up the slack.

And once you’re exercising at about 60 to 80% of your maximum heart rate studies show that your body gets about half of its energy from carbohydrate stores and. From fat stores, and this is a point that scientists refer to as your maximal fat oxidation rate or mfo. Now, if you push even further than that, if you are pushing to near maximal intensities in your training think sprinting for example, or a higher rep set of maybe squats taken close to muscular failure, think like a 10 rep set for example.

What happens is, Your muscles start getting the majority of the energy that they need to do that from carbs and very little from fat. And so if you just connect those dots, you see how this fat burning zone idea came about. The theory was if we want to lose as much fat as possible from our workouts, maybe we should work out at the intensity at which our.

Burns as many calories as possible while still getting the majority of those calories from fat and not carbs. Sounds nice, but there are a few reasons why it’s all hat and no cattle. So the first and biggest problem with this idea is that the amount of fat you burn during a workout isn’t all that important when it comes to long term fat loss.

You see when you burn more fat and less carbs during a workout, you just burn less fat and more carbs later in the day, and vice versa. And the reason for this is studies show that our body will calibrate how much fat in carbohydrate it burns over a 24 hour period to make sure that it’s burning. The same amount in terms of proportions, regardless of what we burn during our workouts.

So for example, let’s say you burn 400 calories during an intense 30 minute run, and most of those calories are coming from carbs because it’s high intensity and your body’s fat-based energy system just can’t keep up. And then the next day you burn 400 calories on a 90 minute walk, and most of those calorie.

Will come from fat because that’s a low intensity activity that your body’s fat-based energy system can keep up with. Now, which of those workouts will burn more body fat? Many people who believe in the fat burning zone will say, Oh, the 90 minute walk, but they’re wrong. You’ll burn about the same amount of body fat.

The key takeaway here then is in the context of fat burning. All that really matters in your exercise, in your training, in your workouts is calorie burning. That is what drives fat loss, not the intensity of the training. Now, the intensity of training drives calorie burning. Very true. But calories are calories.

Energy balance works very simply regardless of what type of exercise you’re. . The second problem with the fat burning zone idea is the way that most people implement it. So what they are often told is they need to hold themselves back in their training. They need to do relatively easy workouts, and that’s what the fat burning zone workouts are if you are even moderately fit, and they then will not do.

Moderate or higher intensity workouts because they think that those sessions are not gonna be as effective for fat burning because they are not in the fat burning zone. As I mentioned a few minutes ago, though, technically the fat burning zone is up to 80% of your maximum heart rate, and that’s something that most people would consider a pretty difficult workout.

That’s a moderate or even a fairly high intensity training session. So for instance, let’s say you do something very easy. Let’s say you go for a walk and you burn off a hundred calories and the majority of those come from fat. Let’s say 85 of them come from fat. That is not going to be as effective as spending that time doing something more difficult.

Let’s say running at a moderate pace, which yes, will burn fewer calories from fat, relatively speaking, but more in an absolute sense. So let’s say in the same time you. 400 calories on that run and 250 of them come from fat. Or maybe you burn 600 calories on a slightly more intense run, or maybe a bike ride or something like that.

And half of them, just 50% come from fat, but that’s 300 calories come from fat. So in a relative sense, yeah, the a hundred calorie walk was. Quote, unquote, more efficient for fat burning. But in an absolute sense, the higher intensity workout was a lot more effective. Now, the last problem with the fat burning zone myth is that it implies it’s a static intensity that occurs at a very specific heart rate.

And cardio machines often reinforce this by showing pretty graphs, and they try to indicate exactly where your heart rate should be for fat burning versus cardiovascular training and the reality. Though is the fat burning zone, or more accurately the term I shared earlier, your maximal rate of fat oxidation can vary widely depending on your fitness level and sex specifically.

People who are in better shape burn a higher percentage of fat at a higher intensity than people who are less fit because studies show that exercise improves your ability to metabolize fat for energy at. Intensities. And on the flip side, studies show that very low intensity exercise can max out the fat burning abilities of obese people that they can reach their maximal rate of fat oxidation at, for example, just 24% of their VO two max, which is the maximum amount of oxygen you can metabolize during exercise.

It’s a another measure of exercise intensity. And then if we look at research on very fit people, on endurance athletes, we see that in some cases they don’t reach their maximal rate of fat oxidation until they’re close to 80% of their VO two max studies also show that women burn a higher percentage of calories from fat than men do at most exercise intensities.

So my point with all of this is the fat burning zone is a moving target. You’re never gonna be able to pinpoint it. Exactly. Now, fortunately, You don’t have to because it’s not necessary. It’s not even useful to do and all that Then brings me to a question, which is, what kind of cardio is best for burning fat?

And the answer is something you’ve probably guessed by now. It’s very simple. It is whatever burns the most calorie. That’s it. Now, that doesn’t mean I’m telling you to only do very high intensity cardio. You only do hit, for example, because while HIT does burn the most calories in the least amount of time, it is also pretty hard on your body.

Even if you choose something that is low impact like biking or rowing or swimming, it places additional recovery demands in your body. And if you’re listening to this show, you’re probably doing a fair amount of weightlifting, a fair amount of strength training, and your priority is to progress there and to make sure you are fully recovering from those workouts.

And in that case, I would not recommend doing a bunch of hit if you want to do some because you want to get the extra calorie burning or the extra. Cardiovascular endurance, then I’d recommend capping it at probably about an hour per week, and I would split that up into two or three sessions. So then the best fat loss cardio regimen for you is gonna be the one that allows you to burn the most additional calories.

Over time. So let’s say you’re gonna be cutting for a few months. We have to look at it from that perspective. And when we look at cardio through that lens, we realize that just a couple of hit sessions per week is inferior to twice or maybe even three times as many lower intensity sessions per week.

If we’re just looking at fat burning, assuming you’re not trying to do one hour hit sessions, you’re not trying to die basically. And the longer term perspective also makes it clear that you need to be doing cardio that you enjoy, or at least that you don’t hate. And unless you have a masochistic streak, you probably don’t really enjoy very high intensity cardio.

You probably more enjoy. What I do, hop on a bike 30 minutes, work up a sweat, push yourself to an effort level of maybe a four or five out of 10, where you’re breathing more heavily throughout your workout, but you can still have a conversation. Maybe you have to catch your breath now and then, and burn a few hundred calories and take a shower and move on with.

And so then that’s my general answer. When people ask what type of cardio they should do or what type of cardio routine they should do to lose fat faster, a fair amount of low slash moderate intensity stuff with small amounts of high intensity stuff, if they feel up to it. All right. That’s it for this episode.

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