Is Cardio a Good Tool For Fat Loss?

There’s a ton of conflicting information about cardio, which makes it far more confusing than it has to be.

Let’s clear up the confusion and get to the bottom of all your cardio questions.

What is “Cardio?”

Cardio isn’t riding a bike or walking on a treadmill with the incline setting.

Cardio is aerobic exercise, meaning that it uses the Aerobic energy pathway (officially called the oxidative phosphorylation system)

It’s one of the three main energy systems in the body:

• The ATP-Pcr System

• The glycolytic system

• Oxidative Phosphorylative system

The third system is the only one that uses oxygen (the first two are too intense — oxygen production can’t keep up).

Performing aerobic exercise requires the heart to pump blood to distribute the oxygen bound in hemoglobin to muscles.

This is why cardio (aerobic exercise) increases your heart rate and trains your heart.

If exercise gets too intense, it crosses the anaerobic threshold (the most intense exercise you can perform sustained by oxygen) and will require one of the other two energy pathways.

Exercise that remains below this threshold is aerobic, meaning you can fuel the exercise with oxygen intake.

This type of exercise (below the anaerobic threshold) is called cardio: jogging, hiking, brisk walks, cycling, etc.

Does Cardio Burn Calories?

Obvious answer here: 

Heck yes it does.

Using oxygen for energy requires work from the body.

Even the breathing you would do if you spent an entire day laying in bed would still burn calories.

But the more oxygen required to fuel activity that recruits effort from more muscles, the more energy you burn.

Hence jogging on the treadmill burns more calories than lying in bed.

The unit to measure exercise intensity from oxygen demand is a MET (metabolic equivalent).

A MET is the oxygen cost of energy expenditure — 1 MET is equal to 3.5 ml of oxygen per kilogram of body weight per minute.

While sleeping or lying in bed, you’re using 1 MET.

But when you wake up and do your morning workout of interval sprints, you require much more oxygen. Now you’re using around 7–8 MET.

The higher the MET, the more energy you use and calories you burn.

Is Cardio Good For Fat Loss?

Well, of course it is. 

Right?

We just established that it burns calories.

This is where things get a bit hairy, and many misunderstand or misrepresent coaches who say that cardio isn’t good for fat loss.

There are a few problems with relying on cardio for fat loss.

You don’t earn dividends from cardio

I love using finances as an analogy for fitness.

You can think of doing cardio for fat loss as similar to working a day job to gain financial freedom.

But in this analogy, you’re not investing any of your earnings.

You’re living paycheck to paycheck.

As long as you keep working, everything is okay — you’re earning enough to keep the lights on. 

But if you reduce your hours or start thinking about retirement, you have a big problem.

Lifting weights and building muscle, on the other hand, is like investing.

We established that muscle requires oxygen, and you’re oxygen requirements determine your energy expenditure.

This works out to:

When you lift weights and increase muscle mass, you increase the energy you consume while lying around in bed.

It’s like earning while you sleep.

Cardio provides some form of dividends, such as a higher red blood cell count and an increased V02 max, but not in terms of fat loss.

Yes, doing cardio can burn calories and cause you to lose fat. But it relies on you continuing to do the same volume of cardio. If you stop or reduce, you have a problem.

For this reason, many coaches will prioritize weight training as a better exercise for long-term fat loss since weight training burns calories at the moment (like cardio ) but also contributes to higher energy expenditure in the long term.

Cardio for Fat Loss distracts from the most important point

The main driver of fat loss is nutrition, not cardio.

This becomes painfully clear when you compare the amount of time it takes to burn off an item of food with cardio.

Let’s say that it’s Thirsty Thursday at your office. 

You go and have two beers and a mini-bag of Lays chips.

That’s 500–600 calories (depending on the beer).

It works out to an hour spent on the treadmill or elliptical machine.

A muffin with your morning coffee = a 3-mile jog

The donut at the office = 45 minutes on the exercise bike.

I don’t want to scare you away from enjoying food, and my philosophy for a balanced life is that you should say yes to these things once in a while.

But when you start comparing the energy in certain foods to the required cardio activity to burn them off, it becomes painfully apparent that 97% of your fat loss progress will come from the choices you make in the kitchen.

As the saying goes:

When you hear a coach (or anyone) saying that cardio isn’t good for fat loss, what they’re really saying is that it’s not the best approach for long-term fat loss.

The best long-term fat loss approach is lifting weights, having a sustainable cardio routine for your heart and lung health, and eating a diet that supports your goals.

What Cardio Should You Do?

The fact that cardio is not the ideal exercise for fat loss doesn’t mean that you shouldn’t do cardio.

Keeping an active cardio as a habit supports a higher energy expenditure and will help you stay lean.

Remember — cardio does burn calories; it should just be seen as less crucial for fat loss than lifting weights and nutritional choices.

Like you’re diet, the essential part of your cardio routine is that it’s sustainable. It should be something that you can stick to for life.

Let’s return to the financial analogy.

Cardio for fat loss is like working a day job to get rich.

If you go through a phase where you’re working overtime 7-days per week, and lifestyle creep adjusts to that volume, what will happen when you burn out and need to go back down to something more reasonable?

You might go into debt from less cash flow.

When people adopt unsustainable cardio habits, a similar thing happens.

 They get a lot leaner as they’re working out excessively for that wedding or vacation, but once they return to their old habits, they’ll regain the weight (and possibly more).

The first answer to “what cardio should you do” is something you can do forever. 

This rule excludes activities like training for a marathon, where you would inevitably increase your cardio training.

But that’s training for sports performance.

Weight loss and weight maintenance cardio should not exceed what you can do consistently as a habit.

What’s the best approach for a typical cardio habit?

I love longevity expert Peter Attia’s approach to this.

Peter frames how he looks at exercise through the lens of training to be the fittest 90-year-old. 

He takes a practical approach to the demands of life, and he suggests that you focus on Zone 2 and Zone 5.

Zone 2 cardio is when your heart rate is at 60–70% of its max; you might get this from walking on the treadmill on an incline at 3.7 MPH or using the elliptical machine on a setting over 10.

Zone 5 cardio is training at your max heart rate. You’ll get to Zone 5 doing exercises like sprinting or going full-out on the assault bike or row machine.

Zone 5 is taxing and challenging to recover from, so it shouldn’t happen too frequently.

Get into Zone 5 for about 10 minutes two times per week.

Zone 2 is a lot easier to recover from. You can’t overdo Zone 2, so the biggest restraint is time.

If you can fit it in, shoot for 40 minutes of Zone 2 cardio four times per week.

Do you have to do Cardio to get shredded?

No.

Many people lift weights and use nutrition (a calorie deficit) to lose fat.

The extra calories from cardio can help, but it’s not necessary.

Does Cardio Kill Your Gains?

This needs to be a whole post in itself — but the short answer is that it comes down to the dose.

Moderate cardio does not interfere with muscle development. It will help because the more able you are to pump oxygen to your muscles, the more you’ll be able to push into higher rep ranges and maximize hypertrophy.

But extreme cardio is difficult to recover from.

Your body can only make so many adaptations, and the adaptation to become bigger and stronger differs from the adaptation to improve endurance.

Going for a few jogs isn’t going to kill your gains, but you won’t be able to build optimal muscle while training for a marathon.

But what about all the jacked dudes who run marathons?

They built muscle first and maintained it while training for a marathon.

Maintaining vs. building are very different.

You can maintain muscle mass while doing intense cardio if you eat enough. But it will be tough to build muscle if you do too much cardio.

Everyone should do cardio for optimal brain, heart, and lung health.

And a sustainable cardio habit helps support long-term weight maintenance.

But the most bang for your buck with long-term body composition is lifting weights and focusing on nutrition.