Is There Really A Post Workout Refueling Window?
So many sports nutrition experts and resources tell you that there’s a “special window” after a workout where you should refuel. Typically that window is reported as 30-60 minutes. Why? Reasons include preventing muscle breakdown, restoring glycogen, helping with protein synthesis, promoting recovery, etc. I’m not a nurse practitioner, not sports nutrition expert, so I’m not refuting those benefits, nor am I saying that you don’t need to adequately fuel your training. However, I came across some interesting research that shows that this super special refueling window might not be as important or as specific as many of us have been led to believe.
Like all things health and wellness, this is not a straightforward subject. There may be times when it’s fine to wait several hours after a workout to refuel as well as times when getting some calories in immediately post-workout makes more sense. There is research to support both sides of this story (which is unsurprising), but the thing to remember is that there are factors that change what needs to happen. 
Most of the studies done on the topic of post-workout refueling that show that there is a benefit to refueling immediately after a workout were done on subjects who worked out in a fasted or semi-starved state. Knowing this, the importance of fueling immediately post-workout makes complete sense. This is the problem with the way a lot of studies are reported in the media, we don’t get the full story so we might not have any idea that the subjects in the study were fasting when they worked out.
Determining Your Post Workout Fueling Requirements
If you ate something before workout out (as much as two hours before your workout) and it wasn’t a hard workout, or you aren’t hungry after your workout, don’t worry about eating right away. There is no critical need to fuel within 30-60 minutes. Nothing bad will happen. 
If you worked out in a fasted state, eat ASAP regardless of hunger or workout intensity.
If you have another workout later in the day, eat after your first workout even if you also ate before you worked out.
If you are trying to gain muscle mass, you need to eat often, so be sure to refuel after your workouts regardless of hunger.
If you have any kind of HPA axis dysregulation (commonly called “adrenal fatigue”) or any other chronic health issue, you should be eating regularly (i.e. not fasting as that causes additional and unnecessary stress). This doesn’t necessarily mean eating immediately post workout, but don’t skip meals.
Pre-exercise amino acid supplementation is almost always a good idea whether you’re eating or not. You can read my blog post on EAAs vs BCAAs here to learn more about why this is important and which option to choose.
The low-carb/keto community has mixed views on protein. Some say too much spikes your blood sugar because the excess is turned into sugar via gluconeogenesis in your liver and others say that process only happens when there is a demand (if you are not fat adapted, under stress, or need immediate glucose for fuel). I tend to take the latter stance on this issue and believe that protein is critically important, especially for athletes.
One study showed that taking 0.5g of protein per kg of lean body mass (the equivalent of 1.1g per pound of lean body mass) both pre and post workout is a “fail-safe” general guideline.  While it may seem obvious for those who are looking to build muscle to eat more protein, this is also a critical component of endurance training too.
Taking in protein from high-quality sources immediately after a workout (within two hours) stimulates large increases in muscle protein synthesis.  Remember that more is not always better and that 20 grams per meal is generally adequate for most athletes to get their desired results (aim for 1.4-2.0g per kg of bodyweight per day during training cycles). 
When To Carb It Up
If you have trained in a fasted state or it’s been more than 3-6 hours since your last meal, plan on eating a snack or meal that contains both protein and carbs immediately after your workout. The harder your workout (both volume and/or intensity) the more important this is.
If you know that your workout will be one where your glycogen stores will be depleted (as in a long workout or race day), eating a hefty dose of carbs (and some protein) immediately after this event will support glycogen synthesis. This can take place within two hours of completing your workout and still be beneficial.
Taking in essential amino acids along with carbohydrates stimulates muscle protein synthesis, especially when consumed one to three hours after resistance training.  Adding carbohydrates can stimulate further increases in muscle protein synthesis, and pre-exercise consumption of carbohydrate and protein results in peak levels of muscle protein synthesis. 
What Should You Eat and When?
However, it does appear that studies show mixed results on whether carbs or protein are a better choice. Some studies say that the mix of carbs and protein is optimal, while others say that protein alone gives you these benefits and the addition of carbohydrate makes no difference.
One study found that eating protein before a moderate-intensity workout increased post-exercise energy expenditure significantly when compared to carbohydrate. This same study also found that fat oxidation was improved post-workout when only protein was consumed prior to the workout. It also found that fasting did NOT create more fat oxidation when compared to carbohydrate or protein. 
In my opinion, it depends on the workout, and even if you live a lower carb lifestyle, there is still a case for consuming carbohydrates. Athletes who are metabolically efficient and able to burn fat for fuel may not burn through their glycogen stores as quickly. This is due to the fact that they are able to use fat for fuel at higher intensities than someone who is not fat adapted.
I think a mistake that a lot of athletes make (especially those who are fat adapted or low-carb) is being in a state of chronic energy deficit while training. I find that this is a more common problem amongst athletes who are trying to lose weight while training for an event. While this isn’t impossible to do, it’s much easier to focus on weight loss during the off season as you don’t run the risk of being in a hypocaloric state while you simultaneously have a larger training volume (this is a recipe for disaster).