Figuring out what to eat, whether you’re looking to lose weight or maximize performance, is only one part of the equation. First, you’ve got to tackle the when. Throw exercise into the mix, and the when-to-eat conundrum gets even trickier. Let’s break it down.

pre workout snacks Should You Eat Before Exercising?

There are two camps here: those who don’t eat or drink before morning exercise (save for a cup of coffee because, hello, caffeine) and those who prefer breakfast before a workout. Many in the first group don’t eat to avoid being sidelined with cramps, while the eaters argue their bodies can’t get going without any fuel in the tank. Both are legitimate points.

But there’s more to it than personal preference. Research suggests the breakfast skippers are onto something. In a recently published study, researchers recruited men who were overweight but otherwise healthy. The men completed a one-hour workout walking at a moderate pace, once without eating before and another time after eating breakfast two hours earlier. The guys burned more fat when they skipped breakfast, and the researchers found exercising in that fasted state also had a positive effect on their metabolism. This was a very small study, and more research is needed, but the findings suggest not eating before a workout of 60 minutes or less—or exercising in a fasted state—may be the way to go for fat loss.

If you can handle it, that is. The working-out-on-an-empty-stomach thing is only helpful if you’re able to successfully perform during your workout, rather than phoning it in or tapping out halfway because you feel like you might faint. In general, most of us have enough energy stored in our bodies to complete a moderate-intensity workout of up to 45 minutes first thing in the morning, says Darin Hulslander, a personal trainer, nutritionist, and CEO of DNS Performance & Fitness, though how long and how hard you’re able to go is affected by what and when you last ate the day before.

And it's worth noting that most people will wake up slightly dehydrated from an overnight fast, so drinking a glass of water (at the very least) is a good idea for all in the morning.

But Doesn’t the Type of Workout Matter?

Yes, it definitely does. You might be able to make it through an hour of yoga without stomach growls interrupting your savasana, but you’d be crazy to set off on a 10-mile run without fueling up before.

“Meal timing and whether or not you should eat definitely depends on the type of training being done,” Hulslander says. “If you’re just walking or getting two or three low- to moderate-intensity miles in, you probably have a reasonable benefit if you don't eat before.” Anything more than that—resistance training, a tough HIIT session, or a grueling endurance workout—and you’re better off fueling up beforehand, Hulslander says.

OK, So What Should I Eat?

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The body taps its fat storage to fuel your empty-stomach workouts (hence the fat burn), but it’s also possible to eat for fat loss. Hulslander suggests fueling up with protein (to help prevent muscle damage) and some carbs (for energy) about two or three hours before exercise. Try something like Greek yogurt with fruit or two eggs with one slice of whole-grain toast in the morning.

Or, if you’re a roll-out-of-bed-and-go person and don’t have that kind of time, try a make-ahead protein shake with half a banana within an hour before exercising, Hulslander says. Aim for 15 to 20 grams of protein—that’ll be a bit easier on the stomach but still give you the energy you need. Even a banana with 3 tablespoons of peanut butter would work.

That rec changes if you’re more concerned about performance than fat loss. When prepping for an endurance session, for instance, your carb intake should go up. A study from the University of Sydney in Australia found taking in between 30 and 80 grams of carbohydrates, or about what’s in a cup of oatmeal and a banana, before working out helps you go longer.

What You Eat After Matters Too

Regardless of whether you eat before, you’ll want to take advantage of the window of recovery, which research has shown to be within 30 to 120 minutes after your cool-down. Aim to take in 16 to 25 grams of protein to refuel the muscles, plus minimally processed carbs such as fruit or starches, Hulslander says.

Don’t worry about eating a plateful of bacon and eggs if you can’t stomach a full meal after exercising. Any protein that contains the nine essential amino acids will do. “There’s no evidence that powders versus whole foods are better after training as long as protein is available,” Hulslander says. And recovery continues 24 to 48 hours after a hard workout, so keep that in mind for your meals throughout the day.

The Bottom Line

The latest research tips in favor of exercising on an empty stomach, so long as your workout is low to medium intensity and your goal is fat loss or maintenance. Just be on the lookout for signs your body isn’t feeling it: feeling dizzy or lightheaded, slowing down significantly in the middle of the workout, a decline in the quality of your movements and form, and/or rapid breathing even if the movements don’t call for it, Hulslander says.

If you’re gearing up for a more rigorous workout, eat some protein and carbs beforehand, because feeling dizzy during a set of burpees is not a great start to the day. Give your body enough time to digest, especially for endurance activities like running, as undigested food in the stomach can lead to gastrointestinal issues (a.k.a. runner's stomach or sprinting to the bathroom instead of your planned run).

After a workout, replace lost fluids with water and replenish with a ratio of 3:1 carbs and protein to ensure adequate muscle recovery and repair.

At the end of the day, everyone is different, and it's up to you to experiment with different pre- and post-workout foods to find what works best for you.

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