You wake up in the morning, and your stomach grumbles. After eight hours without eating, you might be in the mood for a nice plate of eggs and bacon, or perhaps a tasty bowl of oatmeal topped with honey and fruit. Here’s another idea –instead of sitting down for a hearty breakfast, how about lacing up your shoes and heading outside for a run? Not very enticing? What if working out while in a fasted condition, known as “fasted cardio” could help you burn more fat and hit your fitness goals quicker than ever?
You may have seen headlines about fasted cardio. The concept is gaining popularity even while questions still linger. What is fasted cardio? How does it work? And can it really give you the fat-burning results that its ardent disciples promise?
Breaking Down the Fat – Introducing Fasted Cardio
In a nutshell, fasted cardio means performing cardiovascular exercise (such as cycling, jogging, or using an elliptical machine) in a “fasted state.” That’s different than exercising on an empty stomach. You may feel like your stomach is empty an hour or two after eating, but it takes at least four to six hours after eating to be in a truly fasted state. Many fasted cardio practitioners are even stricter and consider eight hours without eating to be the minimum requirement to be in a truly fasted state.
Why put yourself through all the stomach grumbling pain of working out without eating? Those who promote fasted cardio believe that it can help exercisers burn more fat than those who munch down a donut before hopping on a treadmill.
Basically, if you eat a donut before you exercise, you’re loading your body with carbs and sugar. Your metabolism will happily burn those fuel sources instead of the fat you’ve already stored away. This weird quirk of the body harkens back to our caveman days when famine was a common occurrence. Those who could pack on fat and keep it safe were more likely to survive during long, hard winters. For this reason, your metabolic system doesn’t want to burn fat unless it must. By working out on an empty stomach, you deprive your metabolism of its first choice of fuel sources and force it to start breaking down your fat stores to keep your body moving.
A Deeper Dive into Faster Cardio
The idea that your body will automatically switch to burning fat when you exercise on an empty stomach is a somewhat simplistic version of how fasted cardio works. In reality, your body is a complex system, and additional factors help explain why fasting puts your body into a state that promotes “fat oxidation,” which is the scientific term for burning fat.
Eating food, especially sugary snacks or meals, jacks up the body’s insulin levels, which inhibits its ability to burn fat. The beauty of fasted cardio is that since you haven’t eaten anything for at least four hours, your body’s insulin levels are naturally low. This makes it much easier for your body to burn fat.
Low Blood Sugar
Blood sugar, also known as blood glucose, is one of your body’s favorite fuel sources. Right after you eat a meal, your body is awash with glucose. If you head to the gym, your metabolic system will be all too happy to use the easily accessible glucose to power your workout while keeping your fat stores safe. By fasting before working out, your body won’t have any glucose (blood sugar) to burn and will have to dig into your fat stores instead.
When Is the Best Time to Perform Fasted Cardio?
Generally speaking, as long as you can hold off on eating for up to four hours before working out, you’ll be able to put your body in a fasted state and take advantage of the fat-burning benefits of fasted cardio. However, most of us don’t particularly enjoy going for long periods without food during the day, especially if we know an exercise session is just around the corner.
For most exercisers, the easiest and most natural way to perform fasted cardio is to work out as soon as you get up in the morning. After all, you’ve already have not eaten for eight hours. Now you just have to add in a cardio workout, and you’re home free. Many fasted cardio adherents also believe that longer periods of fasting can improve fasted cardio results. It may be better to work out in the morning after eight hours of fasting rather than trying to fast for four or five hours during the day.
Finally, many people are natural morning exercisers. If you and the early bird are best friends, then it will be easy for you to pop out of bed and hop onto your exercise bike. By working out first thing in the morning, you can develop a habit of exercising. Also, there’s no motivation to finish that last mile on the exercise bike like knowing that breakfast is waiting!
Does Fasted Cardio Actually Work?
Ask around the fitness and bodybuilding message boards, and you’ll find plenty of people who swear by fasted cardio, but what does the cold hard science say?
A study in the British Journal of Nutrition seems to back up the anecdotal evidence in support of fasted cardio. Researchers Dr. Emma Stevenson and Javier Gonzalez put the fasted cardio theory to the test by having half their subjects perform a treadmill workout after eating breakfast. The other half of the subjects performed the same treadmill test sans breakfast. The research team discovered that the fasting group burned almost 20% more fat than those who had enjoyed breakfast before their workout.
A second study published in the Journal of Nutrition and Metabolism also found that fasting exercisers burned more fat and also reported less hunger than their snacking peers.
This research suggests that fasted cardio could indeed be a fat-burning booster, but that doesn’t mean this system is right for everyone.
Potential Downsides of the Fasted Cardio Exercise Model
Like any other eating or exercise system, fasted cardio won’t be a perfect fit for every individual. The system also comes with some downsides that you should take into consideration before you give it a try.
One of the biggest downsides of exercising when you haven’t eaten anything for a while is that you may feel sluggish or tired during your fitness routine. This could make it extra difficult for you to maintain the intensity of your workout, and you may even find that you can’t keep up your usual pace.
At the end of the day, losing weight still comes down to burning more calories than you consume. If cardio fasting slows your workout intensity, you’ll end up burning fewer calories, which won’t get you the results that you want. Keep in mind that it will take your body some time to adjust if you usually work out in a “postprandial” or “fed” state. When you make the switch to cardio fasting, give yourself a couple of weeks to get used to the feeling of working out on an empty stomach. If you still feel like you can’t muster enough energy to hit your workouts hard, then cardio fasting might not be right for you.
If you aren’t careful, cardio fasting can be a double-edged sword. When your body doesn’t have an abundance of glucose to burn from your last meal, your metabolism won’t just mind your fat stores for energy. It can also begin to break down your muscles for fuel. Shrinking your muscles is not the result you want, especially if one of your goals is to increase muscle mass.
There are a few things you can do to prevent muscle loss. First, focus on high-intensity interval training (HIIT) rather than long, drawn-out cardio workouts. HIIT workouts entail short bursts of all-out effort followed by low-intensity recovery. (Example – sprinting for 30 seconds followed by two minutes of slow jogging.) HIIT workouts are designed to be short but extremely intense. This will allow you to rev up your metabolism without burning through so much energy that it starts eating away at your muscles.
Next, make sure to incorporate resistance training into your workout routine to promote muscle growth. Resistance training may utilize resistance bands or include weight training with dumbbells or a barbell with weights.
Finally, add plenty of protein into your diet. Think lean meats, eggs, beans, and green veggies. Protein will help you rebuild any muscle that you lose during fasted cardio training.
Is Fasting Cardio Right for You?
Fasted cardio is certainly a promising tool in your journey towards improved fitness and better health, but don’t consider it a magic bullet. If you still eat a stack of pancakes every morning after your fasted cardio workout followed by fast food for lunch and dinner, you won’t lose weight.
Instead, treat fasted cardio as part of a larger fitness plan, which includes dialing in your diet and exercising on a regular basis.
If you don’t like the sluggish feeling you get from working out on an empty stomach, or if you prefer to work out in the evening and don’t want to skip lunch, then that’s fine. Fasted cardio isn’t right for everyone. Even if you work out in a postprandial state, you’ll still burn calories and improve your fitness. In other words, you can still reach all your fitness goals without fasted cardio as long as you adopt good eating and exercising habits.