For some of us, the thought of waking up earlier than usual, skipping breakfast, and heading straight to the gym makes us want to slam "snooze" or order a bagel on Ritual ASAP. But, believe it or not, lots of people prefer working out on an empty stomach, because they believe that "fasted" workouts are better for you.
There's actually some solid science behind the concept of "fasted workouts." Typically, your muscles get energy from carbohydrates in food, explains Tiffany Chag, MS, RD, CSCS, a performance coach and registered dietician at Hospital for Special Surgery. But first thing in the morning, after you've been fasting (and sleeping) for several hours, you've run out of these sources, she says. "If you haven't eaten, your body will have to go find fuel, and it'll go to fat for fuel," she says.
Over time, your body will get used to using fat for energy, and will learn to prioritize fat over other sources of fuel, "which is really good," Chag says. Many people prefer fasted cardio because they believe it will help them lose fat quicker. But actually, the benefits of fasted cardio are deeper: If your body learns how to increase its response to fat, then you'll be able to work out for longer periods of time. "You become more efficient with fuel," Chag says. This shift won't happen overnight, and typically takes a few weeks. But the good news is that you don't have to work out fasted everyday in order to reap the benefits; even two fasted workouts a week can make a difference, she says.
While fasted workouts can be very effective for some people, they're not for everyone. "In some cases, it could be a bad thing to introduce," Chag says. For example, if you're someone who usually works out in the evenings, then attempting to fast all day would be difficult and potentially dangerous. Or if you're training for a marathon and have to run for many hours a day, then fasting beforehand wouldn't be a wise choice because your body needs more fuel. At first, working out on an empty stomach is going to make you feel exhausted, because you're just not used to it, Chag says. "If you're doing a super hard workout, you're pushing your body to an area that it's not prepared for," she says. "That transition period can be tricky and challenging."
That said, if you're eager to try this whole fasted workout thing, you should start with two fasted workouts a week, and see if it works for your schedule and makes your body feel good, Chag says. Technically, you can do any workout in a fasted state, but many people prefer fasted cardio in particular. But you may want to aim for a lower intensity than you're used to the first few times you work out on an empty stomach, she says.
The thing to remember as you experiment with this method is that fasted workouts aren't necessarily "better" than fed workouts — they're just different. "If it fits your lifestyle, give it a shot," Chag says. "And if not, then move on." Plus, there are so many reasons to exercise that have nothing to do with "burning fat." Your workouts should make you feel good, and if doing them on an empty stomach takes away all of the joy, well then that's a pretty clear sign that you should switch your approach — and eat a quick pre-workout snack.