Fasted Cardio for Faster Fat Loss?

How doing cardio in a fasted state can help you lose more weight.

When it comes to fat loss, we’re all looking for tricks or hacks. While there are no shortcuts to getting lean, fasted cardio can be an easy way to boost fat burning.

As with many fat loss strategies, there is mixed information on fasted cardio. The fact is that we don’t fully understand the mechanisms.

However, bodybuilders and fitness athletes have been doing cardio in a fasted state for decades. And I’ve personally seen amazing results using this method.

Of course, it’s not as simple as changing the time at which you do cardio. And there are drawbacks if you don’t do it correctly.

So I’m going to explain everything you need to know about fasted cardio to get the most out of your exercise routine.

fasted cardio faster fat loss?

Taking a break during my morning bike ride to let a family of Canadian geese cross the path. @jeremyfoxfitness

What is Fasted Cardio?

Before we get into the details, it’s important to understand what fasted means. Because it’s not just an empty stomach.

In reality, a fasted state is defined by low insulin levels. Which occurs some time after your stomach empties.

Usually, fasted cardio is aerobic exercise performed first thing in the morning after an overnight fast. But it could be any time of day as long as insulin levels are low.

You see, low insulin levels promote the breakdown of fat for energy. And the more fat you have available for energy, the more fat you can burn.

Benefits of Fasted Cardio

Burn More Fat

The primary benefit of fasted cardio is burning more fat. Multiple studies show that fasted exercise results in a significant increase in fat burning compared to exercise after eating1.

The reason is that when you haven’t eaten in a while your body breaks down fat into fatty acids in a process called lipolysis. Then you can burn (oxidize) those fatty acids for energy.

On the other hand, your body releases insulin when you eat. A hormone that suppresses lipolysis and tells your body to burn more glucose instead of fat.

To illustrate, a University of Texas study compares fat oxidation in fed and fasted cardio. Their data shows the rate of fat oxidation is almost double in the fasted state.

In short, more fat oxidation means more fat loss.

fasted cardio fat oxidation

Adapted from Horowitz et. al2

Promote Insulin Sensitivity

One of the contributing causes of obesity is insulin resistance. Basically, your body develops a tolerance for insulin when you eat too many carbs and don’t exercise enough.

When that happens, insulin levels are continuously elevated. Making it easier to gain fat and harder to lose it.

Fortunately, fasting is the best way to lower insulin. And exercising in the fasted state makes you even more sensitive to insulin.

As a result, you reset your ability to burn fat as fuel.

Build Good Habits

Starting your day on a positive note is another benefit of fasted cardio. When you perform this ritual on a regular basis you affirm your identity as a healthy person.

And that makes building other healthy habits easier.

How Identity Based Motivation Gets Results

Fasted Cardio Workouts

So let’s assume you want to give fasted cardio a try. Do you wake up and just start running like Forrest Gump? Or is there a certain way to go about it to get the best results?

As it turns out, duration and intensity are important factors.

Duration

According to the Nutrition Research Institute fat oxidation reaches a peak after about 75 minutes of exercise3. So there’s no need to go on a cross country trek.

On the other hand, if your cardio session is too short you won’t burn many total calories. For that reason, I recommend at least 30 minutes of fasted cardio for fat burning.

Intensity

Exercise intensity is just as important as duration. Because as intensity increases, your body uses more carbs for energy and less fat.

For that reason, it’s best to target low to medium intensity. Or about 50-70% of your max heart rate.

fasted cardio energy usage

Target 50-70% max heart rate for maximum fat burning

To calculate your max heart rate simply subtract your age from 220. Then multiply by 0.5 and 0.7 to get your heart rate targets.

Example:

If you’re 25 years old you would take 220 – 25 = 195. So your max heart rate is about 195 beats per minute.

From there, multiply 195 x 0.5 = 98. Then 195 x 0.7 = 137. In this case, your target heart rate for fat burning is 98 to 137 bpm.

What about fasted HIIT?

HIIT (high-intensity interval training) is an effective way to burn more fat in less time.

However, that high intensity means your average heart rate is also high. As a result, you burn more energy from carbs than fat during the workout.

In addition, one study found that body composition did not change significantly with fasted vs fed HIIT4. While HIIT is effective for fat loss, doing it fasted does not increase fat loss.

That being said, HIIT is still a good option if you’re short on time. Or if you’re concerned about preserving lean muscle.

What to Eat After Fasted Cardio

Fasted cardio is inherently catabolic, which is good for fat burning. But it can also cause you to lose muscle.

What you eat after fasted cardio determines if you stay catabolic. So the right answer for you depends on your goals.

For example, if you want to build muscle, then you might eat a full meal. Because researchers at Ball State found that protein synthesis increased when participants ate carbs and protein after cardio5.

By the same token, another study showed similar results with EAA’s (essential amino acids) alone6. So you could have a protein shake after your cardio workout. Or supplement with EAA powder to stay in a fasted state.

Fasted Cardio Results

I’ve personally used fasted cardio on and off for years. And I use it with my clients, so I know it gets results.

One example is when I used fasted cardio in preparation for a physique contest. Below is how I looked after dropping about 20 lbs of pure body fat in 16 weeks.

My Fasted Cardio Routine

  • Woke up at 6:30am, supplemented with EAA’s and L-carnitine
  • Performed ~45 minutes of steady state (bike ride) or ~15 mintues of HIIT cardio (hill sprints)
  • Consumed a protein shake with MCT oil post-cardio
  • Had 3 or 4 more low carb meals/snacks throughout the day
  • Performed ~60 minutes of resistance training at 5:30pm
  • Had 1 or 2 higher carb meals post-workout

As you can see, I don’t overdo it with cardio. Usually not more than 45 minutes a day, 6 days a week.

And I don’t waste money on fancy fat burning supplements. Most of which are garbage.

See My Full List of Supplements

Of course, during that time I also lifted weights and followed a strict fat loss meal plan.

Keep in mind there’s no single right way to use fasted cardio. And this doesn’t mean that you should never do cardio in the fed state.

The best routine for you depends on your schedule, body type, and goals.

Key Takeaways

1. Fasted cardio is aerobic exercise when insulin is low

2. Duration should be 30 to 75 minutes

3. Target 50 to 70% of your max heart rate

4. Eat protein or supplement with EAA’s after to preserve muscle

About the Author

Jeremy Fox  –  Founder of Nutritioneering, Engineer, CPT, Bodybuilder, Coach

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