Why exercising on an empty stomach won’t necessarily burn more fat and other weight loss myths


The past year and a half has been difficult for everyone, with a new level of stress that many of us have never experienced before.

A common response to stress is snacking, reaching the comfort of a delicious bag of salty crisps or a block of rich, sweet chocolate.

Combine that with zippers and your jeans could be a bit tighter, or if you’re like me, you live in sweatpants anyway.

Someday, maybe soon, you might want to put those jeans back on.

But don’t be fooled by the untruths on the internet about burning fat through exercise.

Let’s break down three common myths around exercise and weight loss.

First of all: what is fat?

Body fat takes many forms, but visceral fat, which is found around your organs, and subcutaneous fat, which is found just under the skin, are the two that a lot of people want to reduce through. diet or exercise.

Almost the entire volume of each fat cell or fat cell is made up of a single fat droplet.(

Getty Images: Steve Gschmeissner / Scientific Photo Library


Your fat deposits increase when you consume more energy than you use and, conversely, decrease when you use less energy than you use.

To deplete these reserves, you burn or “oxidize” fat. This provides energy for your body to do things like move your muscles during exercise and repair your body tissue afterwards.

Myth 1: I should exercise in the “fat burning zone” to burn as much fat as possible

If you’ve even hopped on a treadmill or elliptical trainer at the gym, you may have spotted a setting that tells you how much you need to exercise if you want to burn fat.

The principle of the “fat burning zone” is based on the idea that, if you train at a particular intensity, your body will preferentially use fat for fuel.

While these zones can vary a bit, they do suggest that you should exercise between 60 and 70% of your maximum heart rate (which you can roughly calculate if you subtract your age from 220) to burn as much fat as possible. .

For most people, this feels like a fairly easy workout.

But is it too good to be true?

Row of people running on treadmills in a gym
Should we get out of the “fat burning zone” so as not to lose pounds in the long term?(

Getty Images: Erik Isakson


If your goal is long term fat loss, I have bad news for you.

While it is true that you will burn more fat by exercising at the “fat-burning” intensity level compared to a much higher or lower level, this is only part of the picture. .

This misconception boils down to extrapolating research data that tells us what is happening at a given point in time, like a snapshot, versus monitoring changes over weeks or months, which reflects real life.

What happens when you stop exercising matters too.

For example, when you train at a higher intensity, you use more other fuels, such as carbohydrates stored in the muscles..

But when you are done exercising, you then use the extra energy to replenish or restore those levels to normal.

You can also use a little more energy to recover from high intensity exercise – a phenomenon known as oxygen debt – and your muscles may also need a little more to recover from higher levels of damage. important during higher intensity exercise.

The result? Little difference in overall fat loss between training in the “fat burning zone” and training at a higher intensity.

And there are some notable benefits to high-intensity training, and it’s not just because it’s faster (because you’re burning the same amount of energy over a shorter period of time).

For example, you retain more muscle and potentially build more muscle with high intensity exercise, which doesn’t happen with long duration low intensity exercise, especially if you eat less and exercise more. in an attempt to lose body fat. .

This doesn’t mean that you shouldn’t be doing low-intensity exercise or exercising in the fat-burning zone. You may be recovering from an injury, having a light day of exercise, or starting a new exercise program.

It just means you need to know that it’s not necessarily best for “fat loss.”

Myth 2: Exercise on an empty stomach for maximum fat loss

Have you heard this one? Exercising early in the morning, before eating breakfast, will help you lose body fat.

The idea is that if you haven’t eaten, fat is the only fuel available for your body to use. That pesky fat will melt away – at least that’s what the internet is telling us.

Like the previous myth, although there is a kernel of truth here, it is not that simple.

When you exercise on an empty stomach, after a night’s sleep, and before you eat breakfast, you are actually using more fat as a fuel source during exercise.

Woman sitting on bed tying her shoe laces
Eating breakfast before you exercise won’t undo all of your hard work. (

Getty Images: Geber86


But my team’s research has shown that exercising on an empty stomach or on an empty stomach does not have a significant impact on body fat in the medium to long term.

So why is this? If you exercise on an empty stomach, your body might compensate by burning less fat after you complete the exercise and eat a meal. This effectively balances the overall levels of fat that you use for fuel.

Interestingly, eating before exercise seems to augment how much energy you use after exercise.

However, there is also a caveat here. Again, most of this research has focused on short-term effects. We don’t know if this translates to more fat loss in the long run.

So if exercising on an empty stomach is something you love to do, then go ahead and do it.

But don’t do it thinking you’re getting the extra benefits.

Myth 3: If I want to lose fat, I have to do cardio

Another common conversation among users is that if you are trying to lose body fat you should focus on cardiovascular exercise.

Well …

The biggest impact on fat loss comes from better eating and drinking habits, rather than exercise – cardio or whatever.

Programs that combine a “nutritional change” with regular exercise seem to have the most benefit.

Young woman taking a break after exercising outdoors
It’s not just cardio when it comes to fat burning. (

Getty Images: PeopleImages


Of course, exercise is part of a healthy lifestyle, regardless of weight loss goals. It just might not have the effect you think it has on your waistline.

And you might not need to do cardio if you’re trying to lose fat.

In research that has yet to be published, my team found that strength training had a modest effect on fat loss in people who were not actively trying to lose weight.

The amount of fat loss we measured was similar to that found in studies of fat loss with continuous aerobic exercise – or even high-intensity interval aerobic exercise.

So what should I do?

The key to successful fat loss is not just exercise, but also creating a significant calorie deficit over time.

In other words, energy in, energy out – which is a pretty good overall summary of how to go about losing fat.

And the take home message: there is no quick fix.

Fat burned during exercise is only part of the complex puzzle of metabolism and weight loss, but there are many ways to achieve your goals.

Just find the one that’s right for you and don’t get carried away by everything you read online or what you hear at the gym.

Dr Mandy Hagstrom is an exercise specialist at the University of New South Wales.

She is also among the ABC’s Top 5 Scientists for 2021.

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