I'm aware that many people on the nutrition section know this already. However I'm making this post just to allow for some new comers to understand that a good diet that adheres to sustainable macros and a concrete demand of calories precedes having that "30-45 minute window of oppurtunity after your work out."
So, put simply, if you forget your protein shake the day of your workout, it doesn't matter, go home and drink it.
Please read the following:
So now what are we supposed to base our nutrition on? Enter the most underrated scientific paper in the last 5 years. Tipton and colleagues (2003) examined responsiveness of protein synthesis for a day after a workout, and found it to reflect a 24 hour enhanced level. That’s right folks, a FULL DAY! This means that having a morning shake will have the same impact on muscle protein synthesis as one consumed following the workout!
These results shouldn’t be too surprising because we’ve known for over a decade that postworkout protein synthesis is jacked up for this long (MacDougall et al., 1995), but if you’re discovering this for the first time, then it’s pretty exciting!
Some research suggests that even 48 hours after the workout our protein synthesis levels can be elevated by ~33% (Phillips et al., 1997), giving us an even longer period during which we can maximize our muscle growth with protein drinks.