Fasted Cardio – Does it REALLY Work?

Everybody is looking for a way to burn more fat in less time, am I right? In this article I am going to destroy a myth that has been flying around since the last century and instead help you become more productive when you workout.

So it all stated in 1999 when Bill Phillips published his bestselling fitness book, Body-for-LIFE, which promised a body transformation in 12 weeks.

In the chapter about cardio exercise, Phillips published his theory that performing aerobic exercise first thing in the morning on an empty stomach maximizes fat loss.

Ever since then every wannabe athlete has been shuffling off to the treadmill each morning before eating as they strive for the best fat-burning workout EVER!

The rationale behind Phillips’ idea was as follows: A prolonged absence of food (like the one you get when you’ve been asleep all night) brings about a reduction in circulating blood sugar, causing glycogen (stored carbohydrate) levels to fall. That leaves your body no choice but to rely more on fat, rather than glucose, to fuel workouts.

He then said that the low insulin levels associated with fasting allow even better fat breakdown, increasing the availability of fatty acids to be used as energy during the exercise session.

I’m sorry to say it but the whole zombie-before-dawn-at-the-gym thing was a big mistake, and I’ll explain why.

Measuring Your Morning Cardio And Metabolism

Above all, we can’t simply look at the number of fat calories burned during an exercise session. Your metabolism doesn’t operate in a vacuum. It’s not a motor or machine that simply turns on and off. The body continually adjusts its use of fat and carbohydrate for fuel depending on a variety of factors.

As a general rule, if you burn more carbohydrates while exercising, you’ll ultimately burn more fat in the post-workout period and vice versa. Now I know you may be thinking, “Who Cares if you burn a few extra fat calories while exercising if an hour later, the ratio shifts to a greater carbohydrate utilization?”

In the end, it doesn’t make a bit of difference. You need to evaluate fat burning over the course of days—not hours—to gain a meaningful perspective on its impact on body comp.

Let’s say you’re a sceptic and figure it’s better to burn more fat now rather than later. Sadly this isn’t right in this case.

While I accept that the research does show that fasted cardio can increase fat utilization during exercise compared to performing cardio in the fed state, this only happens at low levels of training intensity and after a long duration (keep reading to see more about this).

During moderate-to-high intensity levels, the body continues to break down significantly more fat when fasted compared to after you’ve eaten. This sounds good, right? Again not in this instance. This is because you free up more fat than you can actually use for energy, so you have a lot of extra fatty acids floating around in the blood that can’t be used by working muscles.

After your workout ends these fatty acids are shuttled back into fat cells and stored in your body again. So you’ve gone to excessive lengths…only to wind up at the same place.

Fasted Cardio Doesn’t Mean Fast Results

Okay, so after what I’ve just said I bet you’re thinking that you’ll just perform fasted low-intensity cardio to burn those few extra fat calories. Nope, that’s not going to help either. You see, training status also has an effect on the fasted cardio strategy.

If you exercise on a regular basis the benefits of fasted cardio on fat utilization are negligible even at low levels of intensity.

Horowitz and colleagues found that when trained subjects exercised at 50 percent of their max heart rate (this equates to a slow walk) there was no difference in the amount of fat burned regardless of whether the subjects had eaten. 

These results held true for the first 90 minutes of exercise; only after this period did fasted cardio begin producing a favorable shift in the amount of fat burned.

So unless you’re willing and able to slave away on the treadmill for a couple of hours or more, fasted cardio provides no additional fat-burning benefits no matter how fast or slow you go.

Fasted cardio makes even less sense when you take into account the impact of Excess Post-exercise Oxygen Consumption. EPOC, known to some as the “afterburn”, represents the number of calories the body burns after training. Guess what? Eating before exercise promotes substantial increases in EPOC.

And guess where the vast majority of calories expended in the post-exercise period come from? You got it, fat!

What Can We Learn From This?

“The greater the EPOC the more fat we burn, and EPOC is higher if you’ve eaten something before your cardio session”

OK Then, What Should I Eat Then Simon?

The answer depends on several factors, including: 

  • Session duration
  • Session intensity
  • When did you eat before the session
  • individual genetics

As a rule of thumb consume approximately 1/4 gram of carbohydrates and 1/8 gram of protein per pound of your ideal bodyweight (not what you weigh now, what you want to weigh).

For example, if your ideal bodyweight is 200 pounds, then your pre-workout meal should consist of approximately 50 grams of carbs and 25 grams of protein. A shake made of natural fruit juice and whey protein is a good option, particularly if cardio is done early in the morning before breakfast.

Please remember that your individual response to macronutrient intake could be different from this, so use this recommendation as a starting point and adjust it to your own needs accordingly.

You can listen to more about this in the podcast below.

Remember, if you have questions or want me to coach and train you to burn fat, lose weight and get real results look at the packages I typically offer or get in touch today.

Speak to you soon,



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