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Turning Your Body Into a Fat-Burning Machine

Updated: Jun 8, 2022

If you feel like any extra calories you eat go straight to your belly or thighs, you're not imagining things. Those are usually the areas where you store fat because of your genes, hormones, age, lifestyle, and other factors.

Your body tends to hoard calories as fat to keep you alive and safe. The challenge is learning how to get rid of that extra fat.

You hear a lot about fat-burning gimmicks such as working out in the fat-burning zone, spot reduction, and foods or supplements that supposedly burn more fat. Instead of seeking a quick fix that is not likely to work, learn how to burn fat through a variety of types of exercise.

Basics of Burning Fat

If you're trying to lose weight, knowing how your body uses calories for fuel can make a difference in how you approach your weight loss program. You get your energy from fat, carbohydrates, and protein. Which one your body draws from depends on the kind of activity you're doing.

Most people want to use fat for energy, which makes sense. You figure that the more fat you can use as fuel, the less fat you will have in your body. But, using more fat doesn't automatically lead to losing more fat. Understanding the best way to burn fat starts with some basic facts about how your body gets its energy.1

The body primarily uses fat and carbohydrates for fuel. A small amount of protein is used during exercise, but it's mainly used to repair the muscles after exercise. The ratio of these fuels will shift depending on the activity you're doing.

For higher-intensity exercises, such as fast-paced running, the body will rely more on carbs for fuel than fat. That's because the metabolic pathways available to break down carbs for energy are more efficient than the pathways available for fat breakdown. For long, slower exercise, fat is used more for energy than carbs.

When it comes to weight loss, it doesn't matter what type of fuel you use. What matters is how many calories you burn as opposed to how many calories you take in.

This is a very simplified look at energy with a solid take-home message. When it comes to weight loss, what matters is burning more calories, not necessarily using more fat for energy. The harder you work, the more calories you'll burn overall.

Think about it this way—when you sit or sleep, you're in your prime fat-burning mode. But, you've probably never contemplated the idea of sleeping more to lose weight, as lovely as that thought is. The bottom line is that just because you're using more fat as energy doesn't mean you're burning more calories.

Burn Fat With a Mix of Cardio

You may be confused about exactly how hard to work during cardio. You may even think that high-intensity exercise is the only way to go. After all, you can burn more calories and, even better, you don't have to spend as much time doing it.

But having some variety can help you stimulate all of your different energy systems, protect you from overuse injuries, and help you enjoy your workouts more. You can set up a cardio program that includes a variety of different workouts at different intensities.

High-Intensity Cardio

For our purposes here, high-intensity cardio falls between about 80 to 90% of your maximum heart rate (MHR) or, if you're not using heart rate zones, about a 6 to 8 on a 10-point perceived exertion scale. What this translates to is exercise at a level that feels challenging and leaves you too breathless to talk in complete sentences.

But you're not going all out, as in sprinting as fast as you can. There's no doubt that some high-intensity training work can be helpful for weight loss as well as improving endurance and aerobic capacity.

For example, a 150-pound person would burn about 341 calories after running at 6 mph for 30 minutes.3 If this person walked at 3.5 mph for that same length of time, they would burn 136 calories.

But, the number of calories you can burn isn't the whole story. Too many high-intensity workouts every week, can put you at risk in a number of ways.

Potential Risks If you do too many high-intensity workouts, you put yourself at risk for:

  • Burnout

  • Growing to hate exercise

  • Inconsistent workouts

  • Overtraining

  • Overuse injuries

Not only that but, if you don't have much experience with exercise, you may not have the conditioning or the desire for breathless and challenging workouts. If you have some kind of medical condition or injury, check with your doctor before doing high-intensity training (or any kind of training).

If you're doing several days of cardio each week, which is what is recommended for weight loss, you would probably want only one or two workouts to fall into the high-intensity range.4 You can use other workouts to target different areas of fitness (like endurance) and allow your body to recover. Here are some examples of high-intensity workouts.

  • Exercise at a fast pace: For a 20-minute workout at a fast pace, you can use any activity or machine, but the idea is to stay in the high-intensity work zone throughout the workout. You'll find that 20 minutes is usually the recommended length for this kind of workout and most people wouldn't want to go much longer than that.

  • Incorporate Tabata training: Tabata training is another form of high-intensity interval training in which you work very hard for 20 seconds, rest for 10 seconds, and repeat that for a total of four minutes. If you do this workout right, you shouldn't be able to breathe, much less talk.

  • Utilize interval training: Interval training is a great way to incorporate high-intensity training without doing it continuously is by doing intervals. Alternate a hard segment (e.g., running at a fast pace for 30 to 60 seconds) with a recovery segment (e.g., walking for one to two minutes). Repeat this series for the length of the workout, usually around 20 to 30 minutes. A 10-20-30 interval workout is a good example of this kind of high-intensity workout.

Moderate-Intensity Cardio

There are a variety of definitions of what moderate-intensity exercise is, but it typically falls between about 70 to 80% of your maximum heart rate, which would be a level 4 to 6 on a 10-point perceived exertion scale.

That means you are breathing harder than normal but can carry on a conversation without much difficulty and you feel pretty comfortable with what you're doing.5

The American College of Sports Medicine (ACSM) often recommends this level of intensity in its exercise guidelines. The lower end of this range usually incorporates the fat burning zone. Moderate-intensity workouts have some great benefits. Here are some examples.

  • Better health: Even modest movement can improve your health while lowering your risk of heart disease, diabetes, and high blood pressure.

  • Comfort: It takes the time to build up the endurance and strength to handle challenging exercise. Moderate workouts allow you to work at a more comfortable pace, which means you may be more consistent with your program.

  • More choices: High-intensity workouts will usually involve some kind of impact or, at the least, a fast pace. You can usually get into the moderate heart rate zones with a variety of activities, providing you work hard enough. Even raking leaves or shoveling snow, if you do it vigorously enough, can fall into that category.

For weight loss purposes, you would likely want the majority of your cardio workouts to fall into this range. Some examples include:

  • A 30 to 45-minute cardio machine workout

  • A brisk walk

  • Riding a bike at a medium pace

Low-Intensity Activity

Low-intensity exercise is considered to be below 60 to 70% of your MHR, or about a level 3 to 5 on a 10-point perceived exertion scale. This level of intensity is no doubt one of the most comfortable areas of exercise, keeping you at a pace that isn't too taxing and doesn't pose much of a challenge.

This approach, along with the idea that it burns more fat, makes this a popular place to stay. But, as we've learned, you can burn more calories if you work harder, and that's what you want for weight loss.2

That doesn't mean that low-intensity exercise has no purpose. It involves the kind of long, slow activities you feel like you could do all day. Even better, it includes activities you usually enjoy such as taking a stroll, gardening, riding a bike, or a gentle stretching routine.

Low-intensity cardio doesn't have to be a structured, scheduled workout, but something you do all day long by walking more, taking the stairs, and doing more physical chores around the house.

Exercise such as Pilates and yoga are at a lower intensity but help develop your core, flexibility, and balance. They can be a part of a well-rounded routine

By Paige Waehner Updated on December 06, 2021

Reviewed by Heather Black, CPT

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