Fat Burning: Long Duration/Low Intensity Vs. Short Duration/High Intensity

by Mark Mayes Certified Health Fitness Specialist
What is the best way to burn fat—low intensity for a long time or high intensity for a shorter time? This has been an area of controversy and misconception for a long time, mainly because the two concepts are rarely fully explained.

The human body is a very complex machine, and just like any other machine, it needs fuel to perform activities. The fuel the body burns includes fats, carbohydrates and proteins. The body uses each fuel differently, and each—including fats—plays an important role in the proper functioning of the body.

You may be surprised to learn that fat is an important fuel, but fat is not as bad as it is made out to be. It’s actually a high-octane fuel source needed by many systems of the body. Fat delivers the biggest bang for the buck when it comes to energy production. It’s slow burning and produces a large amount of energy per gram. Carbohydrates and proteins, by contrast, are fast-burning fuels that produce less energy.

Consuming the right amount of fuel in all three forms is necessary part of our bodies’ daily function. The problem so many of us face, though, is that we take in more fuel than our bodies can use, so our bodies store the excess fuel. And they store it as fat.

When people want to lose weight—when they want to burn off excess fat that their body has stored—they must produce a large amount of energy; this energy is measured in calories. At nine calories per gram, burning fat releases the most calories. Burning carbohydrates and proteins releases four calories per gram.

Seems straightforward, right? If you want to drop weight, focus on burning fat. Work out for a longer period at a lower-intensity to avoid burning fuels other than fats. Unfortunately this is where things get confusing; the calculation isn’t as simple as it seems.

Most research shows that bodies need to burn a large number of calories each day in order to lose weight. Where the calories come from—fats, carbohydrates or proteins—does not matter. Keep that in mind: the type of fuel is less important than the number of calories burned. It turns out that burning only fat can slow down your weight loss because you actually burn fewer calories. Let’s look at a couple examples to illustrate how this works.

Catherine works out for an hour at a relatively modest intensity and burns 500 calories. Of those 500 calories, 80 percent come from burning fat. An 80 percent return is fantastic, right? Now consider Paul, who works out for 45 minutes at a higher intensity. Paul burns an impressive 900 calories, but only 60% come from fat. It looks like Catherine’s workout is the more effective at burning fat calories, but when we calculate the actual number of fat calories burned, we see a surprising result. Catherine has burned 400 fat calories (500 × .80), but Paul has burned 540 fat calories (900 × .60)!

To date, most research in the area of weight loss supports the conclusion that Paul’s approach—higher intensity for shorter times—is the better approach for effective and efficient weight loss. Not only did Paul burn more calories overall, a higher number of those calories came from fat.

The next question to ask is, “How do I determine the intensity at which I’ll burn the most calories?” What you’re really asking is at what rate do you need to keep your heart beating. The first step in to determining the proper intensity for you is to calculate your target training zone (TTZ). Use the following formula to calculate the lowest and high highest heart rates in your TTZ.

220 minus your age = Maximum Heart Rate (MHR)

MHR × .65 = low end of TTZ

MHR × .85 = top end of TTZ

In order to burn the most calories, work out intensely enough to elevate your heart rate into your target training zone and keep it there for twenty minutes. If you heart rate is outside of your target training zone, you won’t be getting the most effective workout. And as you get into better shape, you will notice that it will take longer for you to enter your target training zone.

To summarize: A person burns a higher percentage of fat calories at lower intensity—in fact you are burning more fat than carbohydrates as you read this—but in higher intensity workouts, that same person burns more calories, and even though the percentage of fat calories burned is lower, the actual number of fat calories burned is higher. Concentrate on higher intensity workouts for shorter periods of time to reach your weight loss goal faster.

Mark Mayes is the owner of Fitness Resources, Inc. in Harrison West. To learn more about how he can help you reach your weight-loss goals, visit http://www.fitness-resources.com.

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