Why Meal Timing Matters When You’re Working Out While Intermittent Fasting

Intermittent fasting is the worst-kept secret in the wellness world, with doctors (like Well+Good Council member Robin Berzin, MD), dietitians (fellow W+G Councilwoman McKel Hill), influencers (ahem, Alison Wu), and celebs (what’s up, Kourtney K) all swearing by its ability to help clear up brain fog, bestow more energy, and manage weight.

There are a few different ways to partake in this nutrition craze, which is especially favored by keto diet fans. Some people eat all of their meals within an 8-hour time frame each day, while others forgo food for an entire 24-hour span each week. No matter how you approach IF, though, it definitely takes planning. And that goes double if you want to make workouts happen, too.

So when, exactly, should you eat when you’re also trying to fuel (and recover from) a workout? According to certified sports nutritionist and former exercise science professor Gabrielle Fundaro, PhD, it depends on the type of sweat sesh you’re into.

“If you’re doing 30 minutes of cardio, that’s fine to do fasted,” she says. (In other words, you can plan your workouts whenever you want.) “But if you’re doing cardio for much longer than that, your body is going to rely on stored glycogen—sugar used for energy for intense activities—to fuel your workout and your performance may not be as good,” she says.

That means if you’re competing or trying to get a PR, going hungry isn’t the best way to do it. Dr. Fundaro works with athletes on the reg, many who love IF, but she always tells them the same thing: “If you do a fed workout instead of a fasted one, you’ll feel a lot better and have better endurance because you’ll have full glycogen levels.” Pro tip: Eat a small meal or snack anywhere between three hours and 20 minutes before your workout so your body has ready glycogen for fuel. If you’re not doing keto, this can be something like peanut butter on toast or an apple with nut butter, and if you’re avoiding carbs, it could be a yogurt (or alt-yogurt) with nuts.

Dr. Fundaro adds that scheduling workouts around your eating window is even more important if you’re doing weight training. In this case, you should eat one to two hours both before and after your session. “You don’t want to do anything with weight and then fasting because you’re actually damaging the muscle tissue, causing microtears,” she explains. Also, make sure that your post-workout meal includes ample protein. “You need protein to rebuild your muscles,” she says.

Yes, IF can be a bit tricky to master, but its biggest rule of thumb is nothing new: Listen to your body. “If you’re hungry, it’s okay to eat,” Dr. Fundaro says. And that goes before a workout, after a workout, or times when you haven’t worked out in weeks.

Some experts actually think intermittent fasting can be unhealthy for some women—here’s the scoop. And no matter when you decide to schedule your meals, everyone can benefit from these snacks fitness trainers stash in their gym bags.