Should You Eat Before a Workout? Science Finally Has an Answer

Updated: May 27, 2020

If you want to burn the maximum amount of fat when you sweat, you'll want to memorize these findings.

There’s a lot of confusion around exercising and eating. What should you eat before you work out? What’s the best post-workout snack? How long should you wait to eat? How will all of this benefit your goal of achieving more muscle mass or losing more fat? With so many questions, there’s surely a lot of differing opinions from enthusiasts and experts alike.

But scientists have now definitively answered one important question: Whether it makes more sense to eat before or after your sweat session.

Timing matters

In a 2017 study, published in the American Journal of Physiology: Endocrinology and Metabolism, researchers from the University of Bath in the U.K. had a group of overweight males walk for one hour at 60 percent maximum oxygen consumption on an empty stomach; then they had them walk again for two hours on another day after eating a high-calorie, high-carbohydrate breakfast. The researchers collected multiple blood samples after eating or fasting as well as after exercising. They also took adipose tissue (fat) samples directly before and after an hour of walking.

The results showed differences in gene expression of the fat tissue in the two trials. The two genes they looked at, PDK4 and HSL, increased as a result of the volunteers fasting and exercising and decreased when they ate before exercising. The researchers believe that the rise in PDK4 likely shows that stored fat was used to fuel metabolism during exercise as opposed to carbohydrates from food and that HSL increased when the fat tissue used stored energy to benefit a boost in exercise. In short: When the volunteers exercised without a pre-workout snack, they burned off body fat instead of fuel from food.

According to Dylan Thompson, PhD, corresponding author of the study, the results support the view that fat tissue often faces competing challenges. “For instance, after eating it is busy responding to the meal, and a bout of exercise at this time will not stimulate the same [beneficial] changes in adipose or fat tissue. This means that exercise in a fasted state might provoke more favorable changes in adipose tissue, and this could be beneficial for health in the long term.”

What exactly is fasting?

How long do you have to forego food to meet their definition of fasting? “It can take several hours to fully finish the response to digesting a meal,” says Thompson, “so the best advice would be to ensure that your last meal was four hours before exercise to get the effect that we reported. Or exercise in the morning before breakfast—this is exactly what we did.” And for a double fat-burning whammy, add this one food to your morning meal. 

It’s actually less important how you refuel post-exercise, especially if you’re pretty active generally. “This is only really an issue for people who are looking to train more than one time on one day,” Thompson says. “This is therefore important for more serious athletes, but for everyone else, it is probably fine to follow a normal meal pattern without worrying too much about refueling.”

After an intense workout—ideally, on an empty stomach—these are some of the best recovery foods.