Both experts agree that the best choice for you depends on what you want to get out of your workout and exercising in general, how long and hard you’re going to work, and how you feel exercising with or without food.
If Your Goal Is Weight Loss or Fat Burning
While it’s true that the body burns more fat during a fasted workout, there isn’t compelling data showing that regularly exercising fasted leads to greater long-term fat loss, says Creasy, though more research is needed in this area.
“For weight loss, I’d focus much more on exercising consistently and finding a routine that feels good, supports a good workout, and doesn’t lead someone to compensate by eating more later,” he says.
“If training on empty leaves you feeling sluggish or unable to get the most out of your workout, there’s really no advantage to doing it,” Ansari adds.
If You Want to Build Muscle or Do HIIT Workouts
Proper nutrition, adequate protein, and resistance training matter much more when it comes to building muscle than whether you eat immediately before lifting, says Creasy. “But eating beforehand may help some people lift more, complete more repetitions, or otherwise get more out of a hard workout,” he says.
The same applies to high-intensity interval training (HIIT): The benefits come from putting your best effort into the session, and if you don’t have enough energy, you may not get as much out of it, says Ansari.
“If your goal is to build muscle and you want to make sure you have the energy to train well, my strongest advice is to get some fuel beforehand,” she says.
That being said, if you feel strong doing a short HIIT workout fasted, you don’t necessarily need to eat beforehand, she says.
If You Have Diabetes or Take a GLP-1
Fasted exercise isn’t automatically better for blood sugar. Exercising after eating may help reduce the rise in blood glucose caused by a meal, says Creasy.
For people who take insulin or diabetes medications that stimulate insulin release, the timing of food and exercise becomes more important because exercise can contribute to low blood sugar, says Ansari.
Medication type, workout intensity, and your usual blood sugar response all matter, so decisions about snacks or medication adjustments should be made with your healthcare team, she says.
Currently, there isn’t much evidence to guide GLP-1 users about whether or not to eat pre-workout, says Creasy.
“Because these medications can substantially reduce appetite and food intake, I’d be more concerned about getting enough protein, nutrients, and fluids and maintaining muscle than about trying to increase fat burning by exercising fasted,” he says.
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