Fasted cardio has long been touted as a viable solution to help you burn more body fat faster than doing cardio after eating. Is this actually true, and if it is, what are the potential benefits and how can you get started?
What is Fasted Cardio?
Fasted cardiovascular exercise is exactly what it sounds like: doing your aerobic work on an empty stomach. While fasted cardio can, technically, be done any time of the day as long as you are in a fasted state, it’s typically done in the morning before breakfast.
But, what is the premise behind doing fasted cardio? Why would anyone want to hit the gym first thing in the morning before breakfast?
The answer is that, for many years, it was surmised that doing cardiovascular exercise on an empty stomach allowed you to burn more body fat than doing cardio in a fasted state. The theory stood that instead of having to burn through all the glucose (sugar) in your bloodstream (from the food you eat) for the first 20 minutes of exercise before it can tap into fat stores, by starting your exercise on an empty stomach, there would be no glucose to use for energy in the blood, so you could tap into fat stores right away.
It’s important to note: if you’re going to do fasted cardio, make sure it’s truly fasted. That is, make sure your body has legitimately had time to digest and process any food you’ve eaten. This is going to be first thing in the morning after a night without eating or at least four hours after eating.
Is Fasted Cardio Really Effective at Burning Extra Body Fat?
This almost sounds like a miracle cure for fat loss—is it too good to be true? Could you actually burn more fat with fasted cardio than by doing cardio in a fed state?
As a matter of fact, it turns out that yes, you do see an increase in fat oxidation (or more fat burning) during fasted cardio exercise. 1
One study from North Umbria University found that those who “exercised in a fasted state burned almost 20% more fat than those who had consumed breakfast before their workout.” 2
But… not so fast.
If there’s one thing we know about the human body, it’s that it is complicated. And while there are benefits to fasted cardio, additional weight loss overall might not be one of them.
Scientists and exercise coaches continue to argue back and forth as to the benefits of fasted cardio over non-fasted cardio with study results often landing on both sides of the fence.
For example, as reported in the JISSN, both fasted and fed groups lost significant weight when combining calorie restriction with morning aerobic exercise, but there were no significant differences between the group that had a meal replacement shake before exercise (fed) and the group that waited until after exercise (fasted). 3
Researchers still insist that it takes your body 20 minutes to start using body fat as a fuel source if you have eaten recently. This is assumed because the food you eat breaks down into what is known as glucose (aka blood sugar). Typically, your body will draw energy from this source (sugar) first before it switches to using fat for fuel.
All true… however…
Scientists remain divided as to the comprehensive advantages of fasted cardio. The body is so adaptable that switching things up in this manner in order to fool it into burning fat for fuel may be a futile effort. Don’t be dismayed, though, as any form of cardiovascular training is going to have immense benefits over no form of training. That said, the benefits of fasted training may be other than what was initially expected. 4
What are the Benefits of Fasted Cardio?
Clearly, any type of cardiovascular training is going to have its benefits. But, fasted cardio may have some additional benefits you can take advantage of if you’re willing to step outside your comfort zone.
According to a study in the Journal of Nutrition and Metabolism, scientists concluded that, “The combination of skipping breakfast and exercising in the fasted state may have an additive effect on suppressing energy intake hours after exercise is completed.” 5
This means doing fasted cardio may set you up for success for the rest of the day. According to their research, exercising in the morning (especially while fasted) can help suppress your appetite throughout the day. A suppressed appetite can lead to eating less over the course of the day, which can indirectly assist with your weight-loss efforts.
Additionally, scientist say fasted cardio can help you burn off fat in troublesome or stubborn areas like the abdomen for men and hips and thighs for women because blood flow typically is increased in these areas during this type of training. 6 So, while you may not burn off more fat in the overall scheme of things, you may just burn off more fat in the stubborn areas.
What Is the Truth About Fasted Cardio and Your Metabolism?
Researchers say that fasted cardio may help by using more body fat for fuel during exercise. But, that doesn’t necessarily mean you’ll burn more fat, percentage-wise, than you would doing cardio when in a fed state. Why?
The truth about fat burning is that your body is a well-oiled machine and has the ability to adapt to stressors. It constantly adjusts its use of carbohydrates for fuel versus using fat for fuel throughout the day.
The Bottom Line
So, what’s the final verdict when it comes to adding fasted cardio to your workout regimen? Well, if you’re looking for additional weight loss by doing fasted cardio over normal fed cardio, you may be disappointed. Recent studies tend to show there is no significant difference in the amount of weight lost (overall) by choosing fasted or non-fated cardio exercise. That does not, however, mean that it has no benefits. And there are other benefits of fasting—whether you enjoy morning cardio (fed or fasted) or not.