Can I Work Out On an Empty Stomach?

From the WebMD Archives

By Cynthia Ramnarace

The Rumor: Working out on an empty stomach burns more fat

I usually run in the mornings, often going from a coma-like sleep to 80 percent of my maximum heart rate in the span of 15 minutes. For a long time, I did this on an empty stomach. I’d read that an empty-belly workout forces your body to burn fat for energy, and wasn’t that my sole motivation for dragging myself out of bed at 5:30 a.m.?

Then I heard that was all wrong -- that we actually need some nourishment before we exercise, because it gives us more energy, leading to more intense workouts. So I started drinking a glass of milk before running out the door. This led to a phlegmy, hacking cough that definitely slowed my pace. After that, I tried orange juice... and I could feel the acid sloshing in my stomach and beating against my diaphragm as I ran.

Frustrated, I went back to my only-water ways. My run might have lacked carb-infused oomph, but at least I wasn’t coughing or acid-refluxing my way through it.

But it turns out that getting some calories in pre-workout was indeed the better idea. I'd just been going about it the wrong way.

The Verdict: Eating the right kind of food before you exercise can improve performance

A routine like mine (exercising first thing in the morning, hours after eating) does force the body to burn fat for fuel. But adopting this approach won’t melt your muffin top. Instead, your body first starts breaking down sugars in muscle tissue.

“Your body doesn’t want to use its fat reserves,” says fitness expert Jenn Zerling, MS, CPT, author of Breaking the Chains of Obesity: 107 Tools. “It wants to use what’s readily accessible. Your body can actually start breaking down sugars from the muscle tissue, and then your liver starts producing sugar. That whole misnomer of, ‘We burn fat as the next-best resource’? It’s not true.” Instead of building muscle during your workout, you could actually be sacrificing muscle in order to fuel it.

Continued

“If you’re doing a killer workout... non-fasting is better,” says exercise physiologist Franci Cohen. “You’ll get to the fat burn because you’re going to deplete carb stores quickly by working out so intensely. You’ll start burning fat within 16 or 20 minutes.”

According to Cohen, there are situations where the fasting workout might work to your advantage -- but they are the exception. “If you’re going for a brisk walk, or even if you’re running or getting on a spin bike, and you’re doing something that’s consistent -- where you’re staying within 70 to 80 percent of your max aerobic [rate] for a continuous hour -- then it’s better to do fasting aerobics,” she says.

But overall, the risks and drawbacks of the fasting workout aren’t worth it. “You risk going into a hypoglycemic episode -- where your body sugar falls -- and passing out,” Zerling says. “Plus, your energy level is not going to be as good as if you had some [fuel] in your body.”

So what should you eat before a workout? Cohen is a fan of low-glycemic, complex carbohydrates that give you energy without causing your blood sugar to spike. Some suggestions include: steel-cut oatmeal; apple slices; carrots with hummus; whole-grain cereal such as Cheerios (no milk); almond butter on whole-grain toast; or an omelet with whole-grain bread. Keep the portion size small, since working out on a full stomach can make you feel nauseous.

Foods to avoid pre-workout include anything that’s going to upset your stomach, such as milk, caffeinated beverages or citrus products. “Any food that’s going to relax the esophageal sphincter is terrible to have before exercise, because you’re jumping up and down and making that muscle jump along with you,” Cohen says. Dairy products are problematic because they encourage mucus production and, for some people, cause upset stomachs -- which can derail a workout.

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