man making protein shake before workout

Is It OK To Work Out On An Empty Stomach?

Fasted workouts, in which you exercise on an empty stomach (usually first thing in the morning before breakfast) have long been a controversial topic among fitness experts.

While a fasted jog may not sound so bad, a heavy lifting session sans fuel might seem downright awful. And what about your gains? Here, experts weigh in on whether working out on an empty tank is a good idea.

Why Skip The Pre-Workout Fuel In The First Place?

Many people who exercise fasted do it hoping they’ll burn more calories from fat during their workout. The idea: Without a hefty supply of carbohydrates (as muscle glycogen or blood sugar) for energy, the body turns to fat stores. Over time, this promotes greater fat loss.  

Some research suggests the theory holds water: A 2016 review in the British Journal of Nutrition, for example, found that people who exercised fasted burned more energy from fat during their workout than people who ate beforehand. Similarly, a 2016 Journal of Nutrition and Metabolism study found that men who performed 60 minutes of fasted cardio not only burned more fat during exercise, but also ate fewer calories later in the day than men who had breakfast before their workout. 

Related: Is The ‘Fat-Burning Zone’ A Sham?

Just how much of a difference this makes, though, is up for debate. A 2014 study published in the Journal of the International Society of Sports Nutrition found no difference in the weight lost by fasted exercisers and non-fasted exercisers after a month of either well-fueled or fuel-free workouts. 

The Case For Eating Before Your Workouts

In addition to having a lackluster effect on fat loss, fasted workouts may ultimately work against your fitness. 

First of all, many people struggle to get through a sweat without any fuel in their bodies. “If you haven’t eaten for several hours, you may not have as much energy to get through your workout,” says New York City-based dietitian and wellness coach Alissa Rumsey, M.S., R.D.,C.S.C.S. “This is especially the case if you’re doing a long or intense workout.”

Eating beforehand may cause you to burn slightly less fat during your workout, but it will make you feel better—and ultimately help you reap greater benefits from your workout. “If you’re able to move a little faster and have a little more bounce in your step, you’re going to burn more calories than you would if you were really dragging,” says board-certified specialist in sports dietetics, Susan Kitchen, R.D., M.P.H.

In the end, that means more fat loss. Remember that Journal of the International Society of Sports Nutrition study? It’s not the only one to suggest that fasted cardio doesn’t give you a leg up on weight loss. 

In fact, a study of overweight and obese women found that both fasted and ‘fed’ participants lost similar amounts of fat after a six-week high-intensity interval training (HIIT) program. Another study found similar results in women who swapped HIIT for an hour of steady-state aerobic exercise.

Plus, if you’re training for a race or competition, exercising fasted limits how well you adapt to your workouts. “If the goal of the workout is to break the body down so that you adapt and become fitter from that effort, then you have to give your body something to work with,” says Kitchen. 

Not to mention, if you go long and/or hard enough, your body may start breaking down muscle tissue to use its proteins for fuel. “When you break down muscle, you don’t maximize your training adaptation,” Kitchen adds. In fact, you literally prevent the gains you’re working for.

To Fuel Or Not To Fuel

Ultimately, pre-workout nutrition is really individual. “Some people find they get through a workout fine without anything in their stomach,” Rumsey says. “Others, though, find that their workout suffers if it’s been more than a couple of hours since they’ve eaten.”

Your ideal workout fuel (or lack thereof) depends on your preferences, schedule, and the type of workout you’re doing. 

If you’re doing a lower-intensity workout that’ll last less than an hour, don’t stress about squeezing in a pre-workout snack or meal. “If you’re going for a light jog or getting on the elliptical for 30 minutes, eating beforehand is not as important, because those activities don’t require as much fuel,” explains New York-based sports nutritionist Heidi Skolnik, M.S., C.D.N., F.A.C.S.M.

Otherwise, going into your workouts with some fuel in your stomach is a good idea.

What To Eat Before A Workout

The longer (think 60 minutes plus) and more intense (think CrossFit®) your workout, the more you’ll benefit from eating beforehand. Even just a snack makes a difference.

Related: How To Build Muscle And Lose Fat At The Same Time

Kitchen recommends fueling cardio with quick-digesting simple carbs (like a banana) instead of slower-digesting complex carbs (like oatmeal). A few go-to’s: applesauce or half a frozen waffle drizzled with pure maple syrup or honey.

If your workout involves a strength component, add 20 grams of protein to your pre-workout snack, Kitchen says. (This will help offset any muscle breakdown.) A cup of Greek yogurt or easy-to-digest protein powder usually gets the job done.

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Whatever workout you’re heading into, experiment with your pre-workout fuel to figure out what works best for you.

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