Our gym’s cross trainer and treadmills have a program called “fat burning.”
Whenever I instruct a new member in our gym on how to use the machines, I passionately educate them about why most programs they see on the cardio machines are useless, especially the fat-burning program.
We are a women ‘s-only gym, and while many of our members are educated enough to include strength training in their fitness program, many still think that cardio – especially in the fat-burning zone – is the key to achieving the fat-loss results they are after.
And so I often find myself explaining what the “fat-burning zone” really is, why it’s not the holy grail for fat loss, and what you really need to do if you want to lose body fat.
In this article, I share the five things I wish everybody would understand about the “fat burning zone” so that cardio equipment manufacturers would eliminate the “fat burning” stickers.
Your Body Never Burns Only Fat
To understand why the fat-burning zone is not all it’s cracked up to be, you must first understand how your body uses the available fuel.
Your body uses energy every second of the day (and night). No matter if you’re fighting through your 20-minute morning jog or chilling on your couch watching Netflix.
Your body needs energy as long as you breathe and your heart beats. This energy can come from fats, carbohydrates, protein, and phosphates. However, your body’s energy source depends on various factors, such as age, sex, how hard and how often you exercise, and your dietary pattern.
As a general rule, the lower your heart rate, the more fats your body utilizes, and the higher your heart rate, the more carbohydrate is used to provide energy. That means when you’re at rest, most of your energy supply comes from fat. On the opposite end of the spectrum would be sprinting, where most of your energy supply comes from carbohydrates.
So, if you want to work out in your “fat-burning-zone,” you’d need to find an exercise intensity above your resting state but below the point where you’re predominantly metabolizing carbohydrates for energy.
If you keep your heart rate below around 60-80% of your maximum heart rate, your body gets around half of your energy from fat.
However, looking at the relative amount of body fat burned is somewhat misleading. As we have seen, you burn the most fat (relatively speaking) when you lie in bed, doing nothing.
But as you can imagine, you don’t burn many calories. Which brings me to my next point.
Just Because You’re Exercising in the “Fat-Burning Zone” Doesn’t Mean You’re Burning a Lot of Fat
What most people miss when they try to lose fat by exercising in the ominous fat-burning zone is that it doesn’t matter how much fat you burn during your exercise session.
First, the total amount of fat you burn is surprisingly little. For example, a study by Tan et al. (2018) showed that the average person burns between 0.1 and 0.4g of fat / minute if they exercise at an intensity where their bodies use most of the energy from fat.
This would equate to a mere 6-24g of fat per hour burned. If you now remember that one pound of fat weighs around 454 g, you won’t be surprised why many people struggle to lose body fat and why the saying “you can’t outexercise a bad diet” is true.
Secondly, exercising in the fat-burning zone burns less total calories and less total fat overall. The following table illustrates this point:
That means even though you might burn relatively more body fat during your workout in the “fat-burning” zone, you actually burn more total calories and, hence, more calories from fat if you work out at higher intensities.
Do you begin to see why the relative amount you burn during your exercise session – and hence the “fat burning zone” matters very little for fat loss?
Your Body Is Smarter Than You
Another crucial aspect that most people trying to exercise in “the fat-burning zone” aren’t aware of is that our bodies calibrate how much fat and carbohydrate we burn over a day. And it doesn’t matter if you burn 500 calories of primarily carbs during a higher intensity 40-minute run or 500 calories of mostly fat during a 2-hour leisurely walk – at the end of the day, you’ll burn around the same number of calories.
Besides, your body regulates how much body fat it burns during a specific exercise intensity depending on your age, weight, diet, and fitness levels.
Highly trained endurance athletes usually burn more fat at higher exercise intensities than couch potatoes, and ketogenic dieters generally burn more fat during exercise than high-carb athletes.
In other words, no one magic “fat-burning zone.” Instead, the “fat-burning zone” is a moving target you can never hit. And so, it is somewhat pointless to base your workout intensity on a heart rate where you’d theoretically burn mostly body fat.
What Really Matters for Fat Loss
So, we have established that the fat you burn during your workout is mainly irrelevant for fat loss. If you can’t precisely target your optimal “fat-burning zone” anyway, what should you focus on if you want to lose body fat?
The most obvious answer that, sadly, many don’t want to hear is a caloric deficit. If you eat below your maintenance, you will lose weight, some of which will be body fat.
However, there are smart and not-so-smart ways to go about losing weight.
If you do it smartly, you will lose mostly body fat and only minimal muscle mass. You will lose muscle if you pick one of the not-so-smart routes. The smart route includes thinking long-term, eating a decent amount of protein, and regular strength training with heavy weights.
The not-so-smart route includes wanting a quick fix and severely undereating calories and protein, focusing on cardiovascular exercise, and neglecting strength training.
Even though many fitness gurus promise weight loss without counting calories to sell you their favorite diet, the truth is that calories matter.
Why You Should Still Do Low-Intensity Cardio
If, after reading this article, you wonder if you should skip your weekly hikes or daily morning jogs and instead switch to doing only High-Intensity Interval Training and lifting weights, it depends.
Contrary to what some fitness influencers would have you believe, low-intensity cardio doesn’t “kill your metabolism” or “destroy your hormones.”
And engaging in low-intensity cardio is an excellent way to move your body with minimal risk of injury. If you do it outdoors, you have the added benefit of spending time in nature.
If you like it, do it.
Just be sure to not cling to the idea that you must stay under a specific heart rate to burn fat and include regular strength training (no Pilates doesn’t count) in your fitness and health regimen.