Fasted Workouts: The New Thinking and Latest Science

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Morning workouts are awesome: Aside from the convenience of getting it done and being on with your day, first-thing-in-the-a.m. sessions have been shown to boost energy all day long. But one of the much-debated and heated arguments in the fitness and nutrition world revolves around whether or not you should eat before those early sessions. So, we spoke to the experts, combed through the latest research, and compiled the pros and cons of fasted workouts.

The pros of fasted workouts:

You may burn more fat

There’s some evidence that fasted cardio workouts (i.e., not eating before you hit the gym) can burn more fat. “Glycogen is the stored carbohydrate that your body uses as its preferred fuel source during exercise,” explains Men’s Fitness Training Director Sean Hyson. “The fasted cardio crowd says that because glycogen is somewhat depleted in the morning after the night’s fast, your body will burn a greater percentage of fat during training as its next resort. Most of us have some sort of meal within two hours before we go to bed and we rarely sleep for more than eight hours; so if you get up and start training 10 or so hours after your last meal, your glycogen will be low, but it won’t be gone. So it could be argued that you’ll have just enough glycogen left to train hard, but low enough levels that you’ll burn more fat than normal to compensate for it.”

It prevents indigestion

Eating breakfast right before you hit it hard at the gym is, in most cases, indigestion waiting to happen. “Too large a meal within a two-hour time frame of activity can slow you down and draw blood from the body to aid with digestion,” says Sam Accardi, R.D., a performance dietitian at Philadelphia-based AFC Fitness and The Charge Group.

You can train yourself to feel less hungry

If you’re the type that wakes up ravenous, have faith that it is possible to get through a workout without eating something first (assuming that you ate dinner the night before.) “You can ween yourself off breakfast if you want to—it just takes time,” says Hyson. “Start drinking water first thing in the morning, and you’ll keep satiated.” And bring gels or a banana along with you if you’re doing a long endurance run (60+ minutes) in case you feel like your fast is impacting your performance too much.

The cons of fasted workouts:

You could “bonk”

Food is fuel, and if you don’t have enough stored up from the night before, it’s possible you could “hit a wall” mid-workout. “I advise having a small snack consisting of protein and simple carbohydrates,” Accardi says. “An example might be a protein bar or a banana with a protein shake.” If you can’t stomach even that much, opt for a small glass of juice, which Accardi says is perfect for boosting blood glucose levels to get you through that morning run. If you’ve only got, say, a half-hour to an hour before go-time, pick solids that digest more quickly, and whatever you do, limit fiber, which is rough on digestion. And again, if you choose to go in fasted, it may be smart to have some portable, easily digestible fuel (like a gel) on hand. (This is less necessary during, say, a 45-minute strength session than it is for something like a 15-mile run.)

You may not be able to train as hard

It’s possible that you couldn’t run sprints as fast or do some other high-intensity exercise as the lack of glycogen in your system wouldn’t allow for it. You’d feel tired and you wouldn’t be able to train hard. Try keeping a log of your workouts and note how you felt during each one and whether it was fasted or not. If you find that you’re just better when you eat first, the benefits of a fasted workout may not be enough to compensate for your performance losses.

You could hallucinate the dumbbells are made of Ding Dongs

Ever been so hungry during a workout that you briefly stop to ponder the nutritional content of a leather weightlifting belt? This is one of the risks you run if you don’t eat something before a workout. But, if happens to you, there are some things you can do. Rather than trying to distract yourself from your hunger, give in to your food-focused musings (well, sort of). “Essentially, you want to shift the hopeless and desperate outlook of ‘I’m hungry’ to a mind exercise involving food planning,” says Juliet A. Boghossian, Behavioral Food Expert and Founder of Food-ology. “Think about what you will eat, the ingredients necessary, preparing it, who you want to share it with: The food is a reward to plan and look forward to following your workout.”

The bottom line:

The real, honest, take-home message is that it really doesn’t matter, says Hyson. “If you want to eat breakfast before a morning workout, go ahead. But if you don’t, it won’t hurt you. You have enough protein and carbs in your system from the night before (assuming you ate dinner) so you don’t absolutely need to load up on more,” he says. Still, one thing to consider is the type of exercise you’re doing. If it’s a super-long cardio workout, you may want to eat a carbohydrate-dense meal about an hour beforehand. And, as mentioned, if you choose to go in fasted—especially to a longer endurance workout—bring along some portable “emergency” fuel. Really, it comes down to weighing the pros and cons yourself and deciding what works best for you and your fitness goals.

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