Fasted cardio is exercising on an empty stomach (first thing in the morning - before breakfast is the optimal time). Fasted can also mean three hours post a meal, but that is not as beneficial as the a.m. cardio.
Before we go into the details about the benefits of fasted cardio, let's discuss a few quick things to consider.
1. Cardio timing is not going to make or break the general person looking to lose weight. It might give you a small edge but in the end it's very low on your list of priorities. What you eat, how often you eat, how much you eat, and getting in your workouts with intensity should all be in place before even worrying about fasted cardio.
2. Convenience is also important. Not everyone can get up with the chickens and not everyone is designed to either. Don't start fasted cardio if it might totally derail you on your exercise schedule. It's not worth it.
3. If you do try it and it makes you sick or after a couple of weeks you notice your cardio sessions just stink in the mornings, you should stop. Trade the a.m. cardio for better, higher calorie burning sessions later in the day OR try consuming a protein only shake 30 min. before exercise. Protein only will help you stay in the same fasted state for cardio while protecting your muscle and give you something on your tummy.
The Benefits of Fasted Cardio
1. When you wake up in the morning after an overnight 8-12 hour fast, your body's stores of glycogen are somewhat depleted (especially if you are on a reduced carb diet and you cut back on carbs late in the day). Doing cardio in this state causes your body to mobilize more fat because of the unavailability of glycogen.
2. Eating causes a release of insulin. Insulin interferes with the mobilization of body fat. Less insulin is present in the morning; therefore, more body fat is burned when cardio is done in the morning.
3. There is less carbohydrate (glucose) "floating around" in the bloodstream when you wake up after an overnight fast. With less glucose available, you will burn more fat.
4. If you eat immediately before a workout, you have to burn off what you just ate first before tapping into stored body fat (and insulin is elevated after a meal.)
5. When you do cardio in the morning, your metabolism stays elevated for a period of time after the workout is over. If you do cardio in the evening, you burn calories during the session so you definitely benefit from it, but you fail to take advantage of the "afterburn" effect because your metabolic rate drops dramatically as soon as you go to sleep.
There are plenty of critics too. I'm a believer in it, though. The non-scientific reason is that too many Oxygen models do it like a religion and they have smoking bodies. Strength trainers for ages have been doing it and I like to think that if it's good enough for the people we all admire in the world for looking their best it is good enough for me.
The other reason I don't subscribe to the cons is that their argument is almost always based on the theory of calories in versus calories out. I just don't think simply slashing your calories is the best, most effective way to lose FAT. I promise if you and I ate the same calories everyday, let's say 1700, exercised the same but I ate a clean diet and you ate candy bars, donuts, and soda that I would look better, lose more weight, and out perform you day in and day out. I'd also live longer but that's another article.
Losing fat is simple and complex. It's simple if you follow a few rules like eating mini-meals, don't eat junk, get in some protein each meal, and drink water, water, water. It can be complex when you time that protein, look at how many and what kinds of carbs you are consuming, etc. Just like fasted cardio, each person needs to decide where their own head is at and then go in that direction. It's funny because most people do best taking the simple approach and they look pretty darn good doing it.
As Tom Venuto says, "there are other reasons for doing cardio first thing in the morning besides just burning fat sources."
1. It makes you feel great all day by releasing mood-enhancing endorphins.
2. It "energizes" you and "wakes you up."
3. It may help regulate your appetite for the rest of the day.
4. Your body's circadian rhythm adjusts to your morning routine, making it easier to wake up at the same time every day.
5. You'll be less likely to "blow off" your workout when it's out of the way early (like when you're exhausted after work or when friends ask you to join them at the pub for happy hour).
6. You can always "make time" for exercise by setting your alarm earlier in the morning.
7. It increases your metabolic rate for hours after the session is over.
What Counts As Fasted Cardio?
There are a few general guidelines you can follow for fasted cardio that will help you stay away from burning through muscle.
1. Do about 30 min. of cardio; much more than that and you risk crossing over into burning through some lean muscle tissue.
2. All cardio counts from circuits to HIIT, to intervals and steady state. Just make sure you sweat and work hard.
3. Have a cup of coffee without sugar. It should help you burn more fat and less glycogen.
4. Make sure you are eating enough protein (30% of your total calories) spread out all day long, taking a multivitamin, and eating a healthy diet. Most people lose muscle because of what they choose to eat, not when they do their cardio.
5. Train with heavy weights if you want to keep muscle. Going light with high reps (15+) doesn't mean you are toning, maintaining, or not bulking. It just means you are wasting your time in the gym.
6. Drink a protein only shake 30 min. prior to exercise.
Can I Do My Weights Fasted?
It depends. When you are in fat loss mode AND you are doing PNP style workouts (lots of circuit style training) you can train on empty stomach, take in a protein only shake if needed, OR you can eat a small piece of fruit if needed.
When you are building muscle you should avoid doing weights fasted because you will not have the energy to lift heavy and make progress.
I typically do my cardio fasted with weights later so that I have eaten at least one meal if not a few. If I do weights and cardio first thing in the morning, I drink an energy beverage called Speed Stack to give me "juice" while working out. After strength, I eat a grapefruit, drink some water, do my cardio and then have my shake. Occasionally I will start my shake 20 min. into cardio if it is a long session.
Optimally, I like to train with protein in my system because I want to make sure I get the best bang for my buck. I would say 75% of the year I train this way and get great results. If I am trying to cut a little fat off I may opt to go straight into the workout.
In the end, each person has to play around with works for their schedule, their life, their energy levels, and how their body responds. There is no absolute, but this should give you a good idea where to begin.