Does Training in the “Fat Burning Zone” Maximize Weight Loss?

Does Training in the “Fat Burning Zone” Maximize Weight Loss?

I have a client who’s interested in building muscle and losing fat. We were wrapping up a session, and while he was cooling down on the bicycle, he asked:

“Andy, I’m in the Fat Burning Zone. That’s good, right?”

I’m sure you’ve noticed on your cardio equipment the mix of buttons and blinking LED lights with a diagram of the “Fat Burning Zone.” But what is this zone, and does it really mean what we think it means?

Well, as you might expect, it's a complicated answer. So let’s take a closer look and clear this whole idea up!

First, it’s important to remember that your body is always burning energy. This use of energy is known as your “basal metabolic rate” (BMR), which refers to the energy required to simply keep us alive. It fuels your brain, organs, and muscle tissue. Amazingly, 60-75% of our total calorie usage occurs without any “activity” at all.

An exercise is a valuable tool for weight loss because it requires the input of more energy from stored resources to match the energy required to complete the task at hand.

Specifically, during low-intensity aerobic exercise, like walking and light jogging, your body will preferentially utilize fat to fuel this type of exercise. This is where the notion of the “fat burning zone” comes from. The fat burning zone represents the intensity level of exercise where your body will burn the majority of calories required to fuel the exercise from fat.

So that’s good, right? Don’t we want to burn calories from fat?  Of course, we do!

On face value, that sounds like a good thing, but not so fast. Although the energy we use at low-intensity exercise does mostly come from fat, the total caloric expenditure is significantly lower. That means, if we want to burn more, we just have to go longer! During low-intensity aerobic exercise, you’re clearly burning more calories than if you were at rest, but because the exercise is not intense, the total caloric expenditure is relatively low.

Let's compare that with higher intensity exercise. At higher intensity levels, the majority of the energy for that activity comes from carbohydrate stored in muscle tissue or available in the bloodstream. When our bodies fuel with carbohydrates, that means less fat burned by proportion. This might sound like a drawback, but higher intensity also means more calories burned! More calories burned equals more potential weight loss.

Wait, what? In the “fat burning zone,” most of the calories burned are indeed from fat. But it’s also true that exercising in the fat burning zone simply uses less calories per minute than exercising in the “cardio zone.” So, what’s the best way to go? Let’s look at an example to clarify:

At rest, nearly 100% of the energy required to keep you alive comes from stored or otherwise immediately available fat.

Now, let’s say we go for a run! As you get up from your comfy couch, grab your shoes, and head out the door, you’re starting to burn more calories because you’re moving. At this point, the balance of fuel sources begins to change. In this case, we’ll say that something like 90% of energy might come from stored fat, and 10% from carbohydrate to fuel the extra movement.

As you break into a light jog (and enter “the fat burning zone”) your body is still selectively burning more calories in the form of fat, while a slightly larger portion comes from carbs. Maybe a 70/30 fat/carb ratio...

As you further increase intensity, your body will begin burning more calories overall. Harder work (faster running) requires more energy. Some of that energy comes from stored fat, and some from stored carbs or carbs pulled in from your bloodstream. The ratio of fat to carbohydrate used is an inverse relationship to intensity.

At around 60-70% of max effort (definitely “running” at this point), we hit what’s called the “crossover,” and our body begins burning a higher relative percentage of energy from carbs than fat. At this point, we would be out of the “Fat Burning zone” on your treadmill or elliptical machine and into the “Cardio” zone. We can continue this trend all the way up the level of effort until at 100% intensity (a full sprint) you’re burning almost 100% carbs and very little stored fat.

So at higher intensities, we may no longer be in the fat burning zone. While that might sound unfavorable, it’s important to remember that we do burn far more calories overall, which leads to greater fat loss overall.

Additionally, at higher intensity exercise, you accumulate what’s called “excess post-exercise oxygen consumption” or EPOC, which marketing has aptly named “the afterburn effect.”

So exercising at a high intensity not only burns more calories per minute, but also builds more metabolic stress. The higher the intensity, the larger the EPOC, and the longer the afterburn. This means more calories burned even after we’re done working out!

Take home message: it would take a much longer workout at a lower intensity to burn the same amount of calories as a shorter, more intense bout.

Neither approach is wrong: remember, any exercise above resting will burn calories, and doing regular low-intensity aerobic work is good for both cardiorespiratory and cognitive health. It also helps us get better at using fat for fuel, which is clearly good.

The fat burning zone is real, but overall you’re burning fewer calories in the same amount of time in the fat burning zone than you could at a higher intensity. If your goal is fat loss, burning more total calories is the name of the game!

So if you’re in a hurry, Increase your intensity, burn more total calories (from both fat and carbs) and get to your goals faster.

For additional ideas and support to help you reach your weight loss goals, reach out to us at GymCloud.

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Andy holds a M.S. in exercise physiology as well as the coveted CSCS certification. He is a self-employed personal trainer and strength coach based in Nashville. When he's not coaching or working out himself, he's got his nose in a book or walking his dog, Jane, at the local park. He likes lifting heavy things, eating BBQ, and drinking local beer.

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