Sure, you’re always fueled up for your workout itself. But what happens after that last piece of iron has been dropped into the rack? After a serious sweat session, your body is pretty much running on empty. Unlike a car engine that stops burning through gas once you turn off the ignition, your body keeps moving, repairing, and replenishing long after you’ve left the gym.

If you don’t follow up your workout with the right intake of macronutrients, your body can’t stop the breakdown of muscle proteins and begin refueling itself, according to fitness and nutrition scientist Cassandra Forsythe-Pribanic, Ph.D., RD, CSCS. The consequence: lackluster results.

So about 15-30 minutes after you crank out your last rep (wait any longer and your blood sugar will plunge), eat some clean, lean protein to help rebuild muscles—and mix in some carbs to get your energy back, Forsythe-Pribanci says. Yes, you need carbs. A lot of them, in fact.

Carbohydrates are the most efficient way to fill up your tank. When you eat, glucose that’s not immediately needed gets stored in the muscles and the liver in the form of glycogen, exercise’s main energy source. If you go low-carb for your post-workout meal, your glycogen-depleted body may actually break down muscle tissue to fuel itself, says Jim White, RD, American College of Sports Medicine fitness instructor and spokesperson for the Academy of Nutrition and Dietetics.

And while healthy fats are key to overall nutrition when you’re hitting the gym, you shouldn’t try to hit your allotment of fat grams in your post-workout grub. Dietary fat slows carbohydrate and protein absorption and minimizes the anabolic effects of insulin in the body, he says.

Now that you know the nutrients you need, here are 12 post-workout smoothies that will help you get them. Bottom’s up.