Should You Work Out on an Empty Stomach?

Photo: Stocksy/Katie Daigneault

To eat or not to eat before a workout? That has long been the question when it comes to timing. There are arguments to be made for both sides (and studies of various credibility to back them up), and this debate is nothing new. But this spring, a new study by researchers at the University of Bath in England found that working out on an empty stomach may have beneficial effects on fat cells. (In this case, “beneficial effects” basically means getting rid of them—it’s hard to understand the specifics without a degree in organic chemistry.) 

Here's the thing: Research is rarely that simple, and besides, losing fat is hardly the main reason to work out.

The small study looked at 10 overweight but healthy men in their 20s (with a jeans size of roughly 41 inches), so it's hard to generalize from its findings alone. Still, it caught the wellness world’s attention, leading to stories like this one, about how “exercising on an empty stomach is the secret to weight loss.”

But here's the thing: Research is rarely that simple, and besides, losing fat is hardly the main reason to work out. However, if you’re considering timing your sweat seshes to your meals, you might as well get some informed opinions. Here, two experts share their different perspectives—and explain how you might want to plan your next fuel-up.

The case for empty-stomach workouts

Cate Shanahan, MD, the physician who created the eating program for the Los Angeles Lakers, says working out on an empty stomach is the way to go. She says that the problem with high-intensity workouts, such as those in the ultra-intense triathlon scene, is that your blood is being diverted away from the gut and toward the muscles. "That is a protective response of the gut," she says. "It can’t digest anything; it would much rather squeeze it right out."

That’s why Shanahan says to put down the fork. “If you’re a regular person going to a 45-minute workout class, it’s absurd to eat [beforehand]," she says. She notes that people store thousands of calories in body fat, and once you start exercising, adrenaline will help your body burn it up.

“If you work out on a full stomach, your body can’t burn body fat very well," she says. "Simply not eating before a workout eliminates the problem of having stuff in your gut and helps you burn body fat better.”

The case for pre-sweat snacks

Superstar trainer Jillian Michaels (with a growing brand—and app—to match), isn't into empty-stomach workouts. "Absolutely not," she says. "The misconception is that if you don’t have any blood sugar available, your body will burn more fat calories while you exercise, but this is not the case." 

She points out that when you work out on an empty stomach, your body's blood sugar dips. "That compromises your intensity and power," she says. “Your inability to train harder, longer, and faster will compromise your calorie burn during the workout, and the bump in metabolism after the workout is over." Plus, she adds, the body needs a certain amount of glucose while exercising—and while fat can't convert into glucose, muscle can. Train on an empty stomach, she says, and you might compromise your gains. 

Of course, observing how your body responds when you've eaten before or after a workout may be the best way to plan your workout regimen—at least until more wide-ranging research is done and a consensus is reached. Meanwhile, as with so many other things, a little intuition can help fill in the gaps.

Whether you chow down before or after your workout, find healthy-eating inspiration from these Instagrammers—then discover the easy way to get out of your workout rut

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