You likely already know that diet and exercise is the best way to begin burning fat. But do you know when that actually happens? When do you stop burning the calories from your breakfast or your lunch, and begin to start burning actual fat stored on your body?
In this guide, you’ll learn:
- The different types of fat your body stores
- Which types of fat burn more easily than others
- When your body begins to use fat as fuel
Are you ready for a mini-course in physiology? Let’s get started!
What is your metabolism?
You’ve probably heard the word metabolism as you prepared to start dieting and exercising. Metabolism is the process by which your body turns food into energy. Your metabolism is what helps your body burn fat, but it’s more than that, too.
Your metabolic processes include the energy you use when you breathe and when you stand. They include the energy burned when you digest your food. Your metabolism includes the energy used to pump blood through your body and your heart. Your liver, your kidneys, your intestines, your lungs and even your growing fingernails depend on your metabolism.
Whether you’re exercising or not, your metabolism is hard at work. In fact, imagine you’re a 40 year old man who’s six feet tall and 180 pounds. Your body burns, on average, around 1,767 calories every day … just by sitting there! So while you’re at the office or even while you’re asleep, your body is burning calories. That same man, walking a mile at a 2.5 mile per hour pace will burn just 96 calories.
Your body is working hard! However, that doesn’t mean you’re burning fat. There are three main types of metabolism. Here’s how they work.
Basal metabolism
Basal metabolism is the metabolism we just talked about. It’s what your body does on its own that keeps you functioning as a living, breathing human. Whether you’re staring at the ceiling in bed at night, watching television or having a conversation with a friend, your basal metabolism is hard at work. This accounts for around 65% of your total metabolic activity every day. (And night.)
Thermic effect of food (TEF)
The second type of metabolism is your digestive metabolism, also called the thermic effect of food. It takes your body energy to break down the foods you eat. Sugar is made from carbs and amino acids from protein, and that takes quite a bit of effort. Different foods take different amounts of energy. For instance, digesting protein burns more than digesting fat. Assuming you’re eating a normal, healthy diet, this metabolic activity accounts for around 15% of your daily calories burned.
Exercise metabolism
The remainder of your caloric activity is what you initiate when you exercise and move. Again, different activities will result in different caloric burn. Here are some examples of what our 180 pound friend would burn doing various activities:
- Stair step machine – 266 calories
- High impact aerobics – 311 calories
- Stationary rowing – 377 calories
- Playing golf – 155 calories
- Skateboarding – 222 calories
- Boxing – 400 calories
- Raking the lawn – 178 calories
As you can see, different activities will net differing caloric burn.
How exercise impacts your metabolism
As your weight changes, the number of calories you’ll burn will change, too. Your resting metabolic rate will change. For weight loss purposes, we’ll state this: the lower your weight, the lower your RMR. That differs from individual to individual, though.
As you exercise and build muscle, your RMR will change as well. The reason for this is that muscle requires more energy to maintain itself than fat does. So, as you build muscle, your resting metabolic rate will increase.
What is fat?
Now, let’s look a little bit at the different types of fat – some are good and some are not. There may be as many as six different types of fat that you’ll read about, but for the purposes of this guide we’re going to talk about the main three: subcutaneous, white and visceral.
Subcutaneous fat
Subcutaneous fat is extremely important fat. Everyone has it, and serves a few functions. First, it protects your organs. Pretty important, right? Next, it protects you when you fall. It helps transport blood to your skin and your muscles. It helps to regulate your temperature. And, finally, it’s what keeps your skin and your muscles attached.
As you can see, subcutaneous fat is super important. But as with all fat, too much can be a bad thing. As you gain weight, you’re more likely to have higher amounts of subcutaneous fat. Your weight loss plan should aim to bring this fat down to a normal level.
Visceral fat, or white fat
Visceral fat is often called “belly fat” but that’s an inaccurate name. In fact, visceral fat accumulates deep within your body, surrounding your muscles and abdominal organs, causing serious consequences. While visceral fat is referred to as belly fat, you can have a completely flat stomach and still have dangerously high amounts of visceral fat.
Some visceral fat is necessary to protect our organs. But too much visceral fat can lead to an enlarged liver, heart disease, type 2 diabetes and other diseases. Visceral fat is also referred to as white fat, generally speaking.
Brown fat
Brown fat is a “good” fat. It’s the type of fat most kids are born with a lot of, and it’s fat that actually burns fat. Kids and babies are the most likely to have brown fat present in their bodies, but adults have been shown to have small amounts of this good fat, too.
Brown fat works sort of like a muscle, burning energy even when you’re at rest. Even if you don’t have a lot of brown fat now, you can actually create it through exercise. When you work out, your muscles excrete a hormone called irisin, which works to convert white fat to brown fat.
When does your body start burning fat?
Alright, that’s enough about physiology. You want to know, “when will my body start burning fat?”
It’s pretty obvious, but we’ll just state the obvious anyway: you’re not likely to burn through your fat reserves when you’re doing nothing. Your resting metabolic rate is usually reserved solely for your bodily functions like breathing, pumping blood and so on. The exception to this would be if you had so little body fat that your body literally had no choice. In that case, you’d likely be hospitalized.
It’s also pretty obvious that you’re not going to start burning fat while you’re eating. Your digestive metabolism is just that: it’s for digesting your food.
So when does it begin? During exercise.
When you exercise, your body goes through several five stages. Some people call them zones. They’re all determined according to your heart rate, which differs for different people. At the end of this guide, we’ll teach you how to find your specific heart rate zones. For now, though, let’s look at the five stages.
Zone 1 – Very light
When you first begin to exercise, you’ll be in zone 1. Most people would consider this a moderately easy walk but again, that will vary depending on your physical activity and fitness level. No matter who you are, though, zone 1 is reached when you’re at 50-60% of your maximum heart rate. Again, we’ll talk about heart rate in a moment. For now, let’s move on to…
Zone 2 – Light
Zone 2 happens with a little more intensity, but you’ll still be able to carry on a conversation with your workout buddy. Your general endurance is improving when you train at the zone 2 rate, and your body is getting better at oxidizing your fat. Zine 2 is defined as 66-70% of your maximum heart rate.
Zone 3 – Moderate
Most doctors and scientists agree that adults should get around 150 minutes of moderate activity each week, and that’s when you’re at 70-80% of your maximum heart rate. For some, this would be a jogging activity. Remember though, if you’ve never worked out before this could simply be walking for you.
Zone 4 – Hard
Also sometimes called “vigorous,” zone 4 is defined as when you’re at 80-90% of your maximum heart rate. You’re probably running at this point, or swimming fast. Maybe you’re sparring. Any way you look at it, you’re breaking a sweat and breathing hard.
Zone 5 – Max
If you’re just beginning to work out, there’s really no need to exercise at your max just yet. Zone 5 is when you’re at 90-100% of your maximum heart rate. You’re unable to carry on a conversation, because your body is using your oxygen. This is not a sustainable zone, nor should you try to sustain this. Lactic acid will build up in your blood, causing you to breathe rapidly and perhaps even experience stomach pain.
Which zone is best for burning fat?
So, if you were to consider each of these fitness zones, which would you think is the “fat-burning” zone? The zone where you’re working at maximum intensity? The one that’s moderate but you can still carry on a chat with a friend?
Spoilers: It’s zone 2. During zone 2, when you’re at around 60-70% of your maximum heart rate, you’ll be burning the most calories from fat. Now, there are some caveats to that. In zone 1, your body is actually pulling more reserves from fat than from carbs. In zone 5, you’re building muscle and creating brown fat which, in turn, will burn more calories in the long run.
But for a sustainable level of activity you can do to build endurance, burn fat and no kill yourself in the process, zone 2 is where it’s at.
How to calculate your fat burning zone
Calculating your fat burning zone is easy if you’re an otherwise healthy person. Please talk to your doctor, as this is simply a generic formula, not specific to your unique needs. Calculating your maximum heart rate incorrectly can cause serious injury and complications.
If you’ve cleared it with your doctor and are ready to find your fat burning zone, here’s what you do.
First, Start with 220 then subtract how many years old you are. This assumes that you’re an adult. That’s your max heart rate. So let’s assume you’re 40. Your maximum heart rate would be 220 – 45 = 175.
Then, find your resting heart rate. As soon as the alarm clock goes off in the morning, take your pulse. Count the beats per minute. That’s your RHR, or resting heart rate. Do that on a few separate mornings to get the most accurate results. And don’t use your thumb – use your middle and index finger.
Now you’re going to need to find your heart rate reserve. Take your max heart rate and subtract your RHR. Let’s say your RHR was 75. That means you’ll do the math: 175 – 75, which equals 100. That’s your HRH and what you’ll use to calculate your target fat burning zone.
Here’s how to find each zone using your heart rate reserve, or HRR:
- Zone 1 = HRR x .5 to HRR x .6 (50 to 60)
- Zone 2 = HRR x .6 to HRR x .7 (60 to 70)
- Zone 3 = HRR x .7 to HRR x .8 (70 to 80)
- Zone 4 = HRR x .8 to HRR x .9 (80 to 90)
- Zone 5 = HRR x .9 to HRR (90 to 100)
Finally, there’s just one more step. Take that final number and add back in your resting heart rate. In our example, it was 75.
Your fat burning zone is zone 2, which lies between 60 and 70% of your heart rate reserve. Add 75 to that number, and that’s your target heart rate to burn fat. 60 + 75 = 135 and 70 + 75 = 145 so your fat burning zone will mean your heart rate will be between 135 and 145.
Remember, everyone’s different. In all actuality, your fat burning zone can be anywhere between 50 and 75% of your maximum heart rate. Be sure to talk to a doctor about your specific needs.
Summary
Your body is always hard at work, burning calories even while you digest food … even while you sleep! But it takes the right kinds of exercise to burn the right kinds of fat. Talk to a doctor or a personal trainer and determine your ideal target heart rate. Then, grab a heart rate monitor and participate in moderately challenging activity, because it’s only then that your body will begin to burn fat.