If you’re in the practice of slurping down a protein shake the second you finish your workout, you’ve probably heard of an intense-sounding concept called the ‘anabolic window.’ And you’ve probably wondered just how much refueling immediately post-workout makes or breaks your results.

The anabolic window (also called the ‘metabolic window’) is a window of time right after a workout when your body is able to restock energy (called glycogen, which we get from carbs) and repair and build the proteins in our muscles at a faster rate than usual, according to a review written by all-star exercise scientists Alan Aragon, M.S. and Brad Schoenfeld, Ph.D., C.S.C.S., and published in the Journal of the Society of International Sports Medicine.

Studies show that without proper fuel, that glycogen restocking slows down and protein breakdown kicks up a few hours after working out.  To combat this—and rev your recovery and results over time—experts recommend you eat carbs and protein immediately after you sweat.

“Our body is like a gas tank, and carbs are the gas,” says Jim White, R.D., owner of Jim White Fitness and Nutrition Studios. Our body breaks down carbs into glucose (a.k.a. sugar), which used throughout our body and stored in our muscles and liver as glycogen so that we’re stocked on energy when we need it later. Meanwhile, protein—which our body breaks down into amino acids—is used to build our muscles and other structures, he says.

Related: Keep your essential amino acids stocked with a supplement.

So the anabolic window is real, but it doesn’t necessarily mean you need to slug a shake or eat as soon as you put down that last dumbbell.

Lots of research supports timing protein and carbs around your workouts—not just after. For example, one study published in Science and Medicine in Sports and Exercise followed guys through 10 weeks of a structured strength training program. Half took a protein, glucose (sugar), and creatine supplement before and after working out, while the rest took it in the morning and at night. The guys who timed their supplements around their gym sessions gained more muscle and strength, and improved their body composition and glycogen storage more than the guys who didn’t.

Though the jury’s still out on the carb sweet spot, studies suggest 20 to 40 grams of protein both before and after exercise offers the most benefit.

How To Make The Anabolic Window Work For You

So what does that mean for you? Well, it depends on a bunch of things—especially when you last ate.

If you down a protein shake or eat a snack an hour or so before hitting the gym, that fuel pretty much covers you through that post-workout anabolic window. In fact, protein or amino acids consumed before exercise can keep the supply available in our blood high for even two or more hours after the workout, according to the review.

So if you have time to fuel up and plan on training for an hour or so, do it with about 200 calories split between carbs and protein (that’s about 25 grams of each), says Pamela Nisevich-Bede, M.S., R.D., C.S.S.D., owner of Swim, Bike, Run, Eat! Nutrition. (If you’re going light or keeping it shorter than 30 minutes, nix the carbs.)

Related: 7 Protein Bars Top Trainers Swear By

If your most recent meal is three or more hours before your workout, though, restocking your glycogen and protein during that anabolic window becomes more important—especially if your main goal is maintaining or building muscle. Go for a snack that’s a two-to-one ratio of carbs-to-protein (like 50 grams of carbs and 25 grams of protein, for example), suggests White.

But if you’re working out first thing in the morning and haven’t eaten since the night before, that’s when your post-workout nutrition is the most important, say Aragon and Schoenfeld. When you’re depleting glycogen and breaking down the proteins in your muscles with nothing in the tank, refuel with something that contains at least 25 grams of protein as soon as you can to prevent muscle breakdown. Keep a protein supplement handy or make sure your breakfast offers enough of the stuff by blending up a protein and fruit smoothie or even mixing protein into yogurt, White suggests.