As you may know, you must burn more calories than you consume in a day in order to lose any weight or body fat [1]. As a result, exercise becomes a relevant intervention to achieve this goal. However, what if there were ways to optimize exercise for fat loss specifically?

Well, that’s the thinking behind fasted cardio or fasted exercise for fat loss. It’s thought to be better than doing your cardio or exercise in a fed state to lose fat. Although, does the research support this? Throughout this article, we’ll talk about why people get behind fasted cardio, if it actually works better for fat loss, and more.

What’s the hype behind fasted cardio?

Let’s say you stopped eating at 8:00 pm one night and then woke up at 6:00 am the next morning to do cardio before your first meal. This would fall in line with the working definition of fasted cardio (although, you likely still aren’t in a true fasted state at this point yet). In this state, you have significantly less carbohydrates available to use as energy to fuel the exercise. As a result, you end up using more fats as fuel while training [2].

Related: Intermittent Fasting Explained

Does this mean fasted cardio works better for fat loss?

At first glance, the thought process behind fasted cardio makes sense. However, there is a problem here. This thinking assumes that fat being used for exercise directly means you are actually losing more fat. Unfortunately, this assumption is incorrect.

If protein and calorie intake are equated, there seems to be no difference in body composition whether you do your cardio fasted or fed [3].

At the end of the day, you burn a certain number of calories and you consume a certain number of calories. If you do your cardio fasted, your body seems to restore that extra energy afterwards once it is consumed. Also, your body will lower energy expenditure throughout the day after a bout of fasted cardio (i.e. fidgeting less, lower respiratory rate, etc.) [3].

Truthfully, the best way to maximize fat loss and minimize muscle loss in a calorie deficit is to eat a high protein diet and resistance train. Everything else has very diminished returns compared to these two.

Related: 8 Tips to Make Fat Loss Easier

Pros and cons of fasted cardio

Even though fasted cardio doesn’t have the increased fat losing capabilities than many people think it does, there are reasons why you might or might not want to do it.

Let’s start with a pro. In terms of time management, I think fasted cardio is great. If you eat a meal before training, you’re ideally going to have some digestion time even if the meal is very small. I don’t know about you, but I’d rather not add that extra time to the morning before I can get to work. So, I incorporate fasted cardio every now and then for this reason.

The big con is a decrease in performance. Carbohydrates are our bodies’ preferred source of fuel for exercise of any intensity. Without them, we are inevitably unable to perform as well. Although, I’d only say this is a big problem if you are training for a race or are a more serious endurance athlete. If you are just recreationally trying to improve your endurance or are doing the extra activity for extra calories burned thorough the day, then I wouldn’t worry about this performance decrement too much.

References

1. Energy Balance and Obesity

   • PubMed ID: 22753534

2. Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis

   • PubMed ID: 27609363

3. Exercising fasting or fed to enhance fat loss? Influence of food intake on respiratory ratio and excess postexercise oxygen consumption after a bout of endurance training

   • PubMed ID: 21411835