Is the anabolic window a real thing?

The old idea of the "protein within 30 minutes after working out" window went...well, out the window! There are a lot of old ideas out there that multiple studies have concluded don't actually matter, but most of them don't hurt anything.

@mewpichu hit the nail on the head, the most important thing is getting enough protein and calories to fuel you and rebuild muscle mass regardless of any strategic timing. As long as you do this, you're doing well.

If you are trying to maximize your timing still, there are some specifics you can consider:

Absorption: Most studies say the body can absorb about 20-35 grams of protein in one meal -- eating more than your body can use turns the rest into waste or worse, gets stored and can lead to extra body fat. Eating three cheeseburgers in one sitting to try and get the full day's worth of protein at once, or chugging down two scoops of 50grams of protein powder to attempt a big boost isn't going to add anything useful.

Different proteins absorb at different rates too. Whey Protein Isolate, for example, absorbs at about 10 grams an hour generally. So a 20-30 gram isolate protein shake takes roughly 2-3 hours to absorb. Egg protein and Casein protein is slower and absorbs at like 3-5 grams an hour.

Don't you still need to refuel after a workout?: Most studies will say as long as you eat something within 2 hours of your workout that it provides the same benefits as the original 30 minute window with no difference. Like @mewpichu said, studies have shown protein before a workout is fine. If you're feeling sluggish or need an extra boost, have more protein before a workout (usuaully wait at least an hour before working out though so your stomach isn't trying to use that blood to digest when you need it to work out). If you're already energized, save protein for sometime after your workout to refuel so you don't get sleepy after an intense session.

Carbs: It also used to be believed that you need to consume fast carbs right after a workout along with protein to bring your blood sugar up and take your cortisol down so the body can absorb and send the protein to the right places. However, recent studies have shown protein alone provides enough of the metabolic effect to do this on its own (I don't remember if that means complete proteins or if some lacking proper amounts of BCAA's are included in that). It's not bad to do it though. Sometimes it's good for energy, though too much food can slow protein digestion so think about what balance you want if that matters to you.

The actual important thing about carbs is to just make sure you get enough to fuel your workout and refuel afterward so you don't feel like an exhausted ton of bricks the next day. A very intense workout might need more carbs before and after (and slow carbs from whole grains, fruit, vegetables, are better). A yoga day or rest day, mild exercise day, etc., doesn't need the extra. And as far as I've seen, carbs do assist in making sure protein is sent to the right places (along with healthy fats in a sense) so it's recommended to get at least some at some point depending on your goals (not knocking the 'no carb' diets if it works for you but I don't recommend them personally).

What about eating every 3 to 4 hours?: The thought behind this is that muscle protein synthesis spikes and falls after 3-4 hours. Can this help maximize protein absorption if you spike every time it falls? Sure. Can it help enough to make a big difference? Most likely not. Again, like @mewpichu said, getting enough protein throughout the day does pretty much the same thing. Depending on your body type, training schedule, etc., maximizing muscle protein synthesis every 3-4 hours can have some benefit but for most of us not enough to make any kind of significant difference where we need to obsess over it. Therefore, If you like breaking up your protein and nutrition into 6+ meals, that's totally fine to go for the 3-4 hour schedule. If you'd rather space it out further and eat 3-4 bigger meals to get your day's worth, that's perfectly fine too. Just get enough throughout the day.

Protein amount for each day: Totally varies depending on your goals. I'll add that consuming too much protein gets dangerous and consult with your physician if you feel like you need higher than what most sources recommend (as someone recovering from overworked kidneys, definitely don't overstrain them with something useless like more protein than you need or can benefit from).

Sources: You'll find a ton of this stuff everywhere, but there is so much that it can get overwhelming to cross reference it all. Places like livestrong.com, verywellfit.com, healthline.com, etc., will all have multiple articles each saying about the same thing. I really like this incredibly comprehensive post from NutritionTactics. It sources a ton of different studies, compiles a lot of this information into one place, lays it out so you can find what you need, and creates graphs and charts that visually show you why there are some benefits to timing but how they are usually so minimal that it doesn't matter so much.

TL;DR @mewpichu is right. There are some other things to consider with timing and some specifics that might make a small difference but ultimately just get enough for pretty much the same effect. Check out the comprehensive NutritionTactics post on muscle protein synthesis to see more with graphs, charts and listed sources if anyone is interested enough.

My understanding is that the anabolic window may or may not be a thing depending on the source, but with how digestion works, you can't really line up the moment absorption with said window. I believe there are some studies out there showing that the timing of eating pre vs. post workout didn't have a large impact on muscle gain as opposed to just making sure you're getting enough calories and protein on a daily basis.