Myth – “Fasted Cardio is the Best for Getting Lean”

Posted on Feb 01, 2019

Aside from the notion of having to eat tuna, rice and broccoli 6 times per day, and downing a whey isolate and dextrose shake immediately post-workout, one commonality you’ll always find in bodybuilding cutting plans is fasted cardio.

You flick open the page of your favourite mag, and there it is …

06:00 – 45 minutes low-intensity cardio

Big and bold – what a way to start your day!

It kind of sucks. I mean, who wants to get up early, and for the first thing they do to be hop on a treadmill, or while away time on a stationary bike, especially if you’ve not even eaten.

I don’t know about you, but I’m a foodie, and I love my breakfast – tell me to train beforehand, and it ain’t going to be pretty.

But if we really need to do fasted cardio to get shredded, I guess that’s how it’s got to be … or is it?

Where This Myth Stems From

The idea of fasted cardio being more efficient for burning fat is based around the concept of fuel sources.

After fasting overnight, your levels of glycogen (the body’s stores of carbohydrate) will be lower. Additionally, you’ll have less readily available fuel, due to not having eaten for anywhere from 6 to 10 hours.

This, therefore, had the bro scientists of 40 years ago claiming that by not having as much fuel available to get you through your cardio, that the body would more efficiently tap into its stores of body fat in order to give you energy for your session.

Fasted Cardio DOES Burn More Fat!

Say what?

So it’s true … fasted cardio is better for fat burning.

Let’s take a look -

What happens is, if you were to measure someone’s blood following a bout of fasted cardio, you would find that a lower proportion of carbohydrate would be used as an energy substrate compared to if they’d just eaten a carb-rich meal.

However, it’s important to note that this doesn’t directly equate to an increase in burning body fat.

It could be a case that actually, you’re burning off more dietary fat that you ate the day before, or, worse – you’re burning protein and muscle tissue.

Hence, fuel substrate shouldn’t be used as an indicator of what you’re actually burning.

The Energy Issue

The number one factor in any diet (whether we’re talking about burning fat or building muscle) is calorie balance.

When training to get lean, you’ll get faster results with a bigger calorie deficit – i.e. the more calories you burn through training, the better.

This means that the most effective form of cardio is the one that burns the most calories in the shortest amount of time.

By training fasted, the vast majority of people will find that they simply can’t work as hard, and therefore, will burn fewer calories. Think about it – how much better do you feel training an hour or two after a high-carb meal than you do dragging your butt out of bed, making your way to the gym and hitting up your session while still groggy eyed and drowsy?

Therefore, if fasted cardio means you don’t put in as much effort as doing cardio after a meal, why would it be superior!?

Burning Fat or Burning Muscle?

In the grand scheme of things, performing cardio fasted is unlikely to burn off a huge amount of muscle, but when you’re trying to optimise everything, you don’t want to lose ANY muscle mass.

Hitting up your cardio session before eating is much more likely to lead to muscle wastage than a fed session. The “bros” often try to side step this by recommending a BCAA shake before a fasted session – but if you do that, then you’re not really training fasted.

What the Science Says

Recently, a comprehensive study by super-smart dude Brad Schoenfeld hit the headlines when it was published in the “Journal of the International Society of Sports Nutrition.”

When comparing the results of two groups (one following a fasted training protocol, the other a fed protocol) it concluded that –

“Both groups showed a significant loss of weight (P = 0.0005) and fat mass (P = 0.02) from baseline, but no significant between-group differences were noted in any outcome measure. These findings indicate that body composition changes associated with aerobic exercise in conjunction with a hypocaloric diet are similar regardless whether or not an individual is fasted prior to training.” (1)

Stop the Steady State

Another point to mention is that whenever fasted cardio is suggested, it’s ALWAYS low to moderate steady state.

The jury is out on the efficacy of steady state vs. HIIT (high-intensity interval training) but the research seems to suggest that HIIT is better for muscle preservation, fat oxidation and fitness.

Not just that, but it gets cardio out of the way much quicker!

That’s why I’ll always recommend HIIT first and foremost, and HIIT definitely works better after eating.

Practical Recommendations

If you genuinely enjoy doing steady state cardio fasted, it fits your schedule, and you’re getting the results you want – keep doing what you’re doing.

However, if you’re looking to get the best results possible (and save yourself a hell of a lot of time and suffering) I’d recommend switching over to HIIT cardio and doing it in a fed state.

You’ll have more energy, burn more calories, lose fat faster and get an hour’s extra sleep too.

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