This is an excerpt from Diet Lies and Weight Loss Truths by Melody L. Schoenfeld & Susan M. Kleiner.
Gym bros have been touting the anabolic window for as long as I can remember. “I gotta down this protein shake now,” they explain from the weight bench at which they just finished their last set, “or I’ll lose all my gains.” The anabolic window is some specific time slot directly after training in which carbs and proteins need to be consumed to make whatever work you did in the gym that day really takes effect.
Eating proteins and carbs after an intense training bout serves the purpose of putting glycogen (i.e., muscle fuel) back into your cells. This can be really useful for people who are, for instance, ultra-endurance athletes (and therefore need to refuel during their many hours of exercise), or who train multiple times per day and need to prime their bodies for their next event or workout (107).
Consuming proteins and carbohydrates after training is also thought to help rebuild and repair muscle after training, particularly by spiking insulin levels (insulin can help increase muscle growth). This hasn’t really been shown to work as expected in research, though—insulin spiking doesn’t seem to affect muscle growth after training that much (107).
For most people, there is no urgent need to refuel muscles in a timely fashion after working out, and neither performance nor physique will really be affected if you wait a few hours after training to eat (107). It’s certainly not going to cause a problem to get your protein in right after training, but don’t stress out about it too much if that isn’t an option. Generally, the time between your pre-workout meal and your post-workout meal should stay within three to four hours if you want to really maximize your results. If you’re training while fasting, it’s probably a good idea to eat something protein-y and carb-y much sooner after your workout. If you ate a really large protein meal before training, you might be able to go up to six hours between fueling sessions after training. Your body is more concerned about you meeting your daily carb and protein requirements, so unless you have very special athletic or physique goals in which even the tiniest change can make all the difference in the world, make that your priority rather than watching the clock (107).