Waking up to make that 7 AM boxing class is enough of a challenge already. Getting out of bed with enough time to eat breakfast before running out the door? That might take a miracle.
Plenty of people work out on an empty stomach (often referred to as a “fasted state”), but whether or not that’s beneficial has been debated for decades, says Steve Ball, Ph.D., associate professor of nutrition and exercise physiology at the University of Missouri. Why? “It is complicated and one size doesn’t fit all.” Here’s what we do know:
Eating carbohydrates before a workout will give your body energy to power through.
Your body turns to carbohydrates when it needs energy. During prolonged exercise your body dips into its stores of glycogen for fuel, says Kelly Pritchett, Ph.D., assistant professor in nutrition and exercise science at Central Washington University. “Glycogen is the storage form of carbohydrate in the body,” she explains. By topping off your carbohydrate stores with a snack, you help ensure your body has adequate energy for a tough workout. This is why experts, including Pritchett, recommend eating “a meal high in carbohydrates, moderate protein, and low in fiber,” about two to three hours before working out.
“Physiologically speaking, it is not dangerous to exercise on an empty stomach,” Ball says. But having a snack might give some exercisers the energy to work out harder than if they were to try on an empty stomach. “I would just ask yourself if you are getting the most bang for your buck during your workout,” Pritchett says.
Some people may not feel like they need food right before a workout, though, and that’s totally fine.
The type of workout you’re doing that day, your level of intensity, and your fitness goals can all change whether or not an empty stomach is sufficient, explains Pritchett. If you feel good throughout your workout and don’t have to sacrifice intensity, then you may be a person who runs well without a pre-workout snack. But mentally, some people just do better with a little food in their stomachs, Ball says.
There has been some research showing the potential benefits of exercising, particularly doing cardio, in a fasted stated in relation to fat burn and endurance. However other research has shown that eating before training is more conducive to fat burn, Ball notes. Because of these contradictory findings, and since there are so many variables at play—including your starting fitness levels and diet, the type of workout you’re doing, and your ultimate goals—there is no conclusive answer. Ultimately, you need to just listen to your body to figure out what works best for you—both physically and mentally.
Either way, staying hydrated is essential for everyone. Working out when dehydrated may increase your risk for cramping (especially if you’re working out for long periods of time and losing a ton of fluids through sweat), and not getting enough H2O in general can make you feel sluggish and sleepy. It may take some experimentation to find the proper hydration needs for you, but registered dietitian Jessica Jones has previously recommended drinking one cup of water for every 15-30 minutes of intense physical activity.
Bottom line: It all comes down to personal preference and doing what helps you perform your best.
Potential benefits aside, there’s no danger in working out on an empty stomach—as long as it doesn’t prevent you from working at your full capacity or alter your ability to be mentally and physically present during your training session. If you get a just-as-good or better workout on an empty stomach, keep doing your thing.
“The post-exercise meal is much more critical,” Ball notes, so make sure you’re refueling with a protein-heavy snack after your sweat to help your muscles repair themselves and maximize the benefits of all the hard work you just did.