On paper it makes perfect sense:
If food provides fuel for energy.
And there’s no food in your system before a workout.
Then your body has to look for other sources of energy to fuel your workout.
Therefore, if you don’t eat before you do cardio, you will immediately watch the pounds fall right off!
Not so fast. As much as the above statements might make sense, they might actually be the reason why so many people struggle to lose weight. The act of losing fat isn’t as simple as flipping on a switch. It’s actually a much more complicated process that involves a combination of many factors. While fasted cardio might not be harmful to your body, fasting before exercise isn’t necessarily making the fat loss process any more efficient. So that leaves the question: Is fasted cardio really that much better for you than any other way of losing weight?? To really under stand what’s best for your body, it helps to understand how fat loss occurs. Fast loss can be broken down into the following factors:
Total Calories Burned (Calories In vs. Calories Out)
In order to lose weight you obviously have to burn more calories than you eat. But research has shown that fasted cardio does not increase the amount of calories burned as compared to when you do cardio on a full stomach. Even more so, fat loss is shown to be directly linked to workout intensity – which can be severely decreased by not having the energy stores to keep going. So better to eat a little something and push harder than to tap out early because you don’t have the strength.
I’m going to assume your goal here is to lose fat while retaining lean muscle mass? For that to happen, you want to focus on protein retention. But when you exercise fasted, it can actually double the amount of protein being broken down – which means that all this hard work early in the morning at the gym might actually be eating away at your hard earned muscle.
Research has shown that the best way to accelerate the fat burning process is to do cardio at a lower intensity for a long period of time (like hours and hours at a time). But who has enough time in the day to spend hours on the treadmill???? So why not just do a little HIIT workout and bump up the intensity while cutting down on the time?? Well, problem here is, when you perform high intensity cardio fasted, you breakdown fat faster than you can actually use it for energy. And when you have too much fat floating around that can’t be used up for energy, it unfortunately just moves back into your fat cells for storage.****
That Sweet Sweet Burn
The last factor to keep in mind when discussing fat loss is EPOC (Excess Post-Exercise Oxygen Consumption). EPOC is when your body keeps burning fat and calories after you stop training. The main reason why weight training is so effective at changing body composition is it’s EPOC or it’s ability to keep your metabolic furnace burning away after you complete your workout. And while this does happen, it actually happens even MORE if you eat prior to working out than if you workout fasted.
Bottom line: Though you might feel better without food sloshing around your system while doing cardio, fasted cardio does not have undeniable fat loss benefits. Does it work for some people? Sure. But will it work for all people? Probably not. Different people work out best under different conditions, and deciding whether someone should eat or fast before exercising is like telling them what time of day to work out of what diet to follow. These choices all depend on what works best for the individual.
**** Sidenote: Even though steady state cardio workouts burn more calories DURING the workout, HIIT workouts lead to as much as twice the fat loss. Even though the slow-and-steady cardio programs burned more TOTAL calories and fat DURING the actual workout, the HIIT programs somehow led to greater total fat loss. This is because the HIIT workouts burned more calories and fat the rest of the day (EPOC!!!), which adds up to more calories and fat than you can burn during a single workout. (ISN’T EXERCISE SCIENCE SOOOOOO CONFUSING?!?)