Anabolic Window
Although I am unsure as to how long this idea has been around, there has been a pervasive theory (and I use that word loosely) that we accrue more muscle and increase recovery if we consume protein immediately after a workout – this has been aptly named, the anabolic window. In this article, we will discuss if such a window exists, as well as understand the physiology explaining its existence or lack.
What is the Anabolic Window?
The anabolic window is the idea that timed protein consumption is necessary to see “optimal” muscle growth.
Does the Anabolic Window exist?
Cutting to the point, yes.
The idea came about some time ago that a post-exercise protein intake is key to complementing growth, and the sooner one can consume said protein, the sooner the body will be able to take advantage and get to rewarding your physical labor. This notion is correct, but not contextually regulated as it should be.
So, let’s add context.
There are a couple studies that show the protein timing is necessary to see increases in muscular hypertrophy and strength [1][3]. However, there are also several studies that show an opposite conclusion; essentially, that protein timing isn’t as big a deal as we’d initially thought [2][4][5][6][7][8]. It turns out, they’re all correct – say what??
The key ingredient is in the details as the studies that found an effect tended to have particular confounding variables left unaccounted for, like total caloric intake may have been measured, but was insufficient to see substantial gains in either condition; or, protein intake was woefully low for resistance training individuals, or even the subjects were elderly, needing more protein to see benefits [1][3]. This means that smaller factors like protein timing may play a more important role, because foundational practices (energy needs, total protein intake, quality protein intake, etc.) were not necessarily met.
On the other hand, if protein values meet sports nutrition recommendations for strength training individuals, the effects of protein timing disappear as both energy intake and protein intake are set at appropriate levels, leading to similar hypertrophy and strength gains in those who consume nutrients immediately post workout or those who wait hours before eating [4][6][7][8]. However, this does not mean protein timing does not matter, just not as much as more important variables; yet, there is one situation in which protein timing may matter more, even in a day to day nutrition rich environment.
If a person consumes protein prior to exercise, there is no need to consume protein again immediately post workout [6]. However, if a person exercises fasted, then it may be beneficial for protein to be consumed quickly after training [5]. It will also matter on the quality of protein, so focusing on proteins rich in leucine (ex. Whey protein) is recommended, no matter the situation [8].
So, for practical understanding: Eating a meal consisting of 25-30g of protein (some carbohydrates), including the leucine amino acid, anytime within 2 hours, pre or post work out, as well as consuming adequate total protein by the end of the day is the best possible scenario for maximizing muscle growth; however, if the latter is met, this is the most important variable to meet.
Understanding the
Physiology
Context matters, because it is dictated by your physiology – of course.
If you are fasted and exercise, there is a substantial increase in proteolysis (aka, protein breakdown), up to 50% increase and can stay elevated for over 24 hours [8]. So, while some proteolysis is necessary, we’d rather not be in a negative nitrogen (protein) balance for too long, as this is counterintuitive to the goal of muscle growth. Fortunately, increases in serum amino acids and glucose can attenuate this increase in proteolysis due to their promotion of muscle protein synthesis through amino acid entry to the cell, as well as insulin’s anabolic effects to shuttle glucose (energy) into the cells. These two actions, and at the very least the increase in amino acids from consumption of protein, helps keep us in a positive nitrogen balance – leading to muscle accretion over time.
So, taking a step out of our cells, if we eat nothing for hours (fasting, possibly overnight?), and then we exercise, proteolysis increases to attenuate the need for muscular repair, as well as oxidation for energy. If you are not feeding the body amino acids and glucose through protein and carbohydrates, it will find them other places across the body – this is a problem, if repeated over and over again. However, if you were to consume protein and/or carbohydrates, the body now has supply to tap into, located in the blood stream – problem solved. Fortunately, this is true for more than a short time as it is true for hours. So, consuming protein pre-workout elevates blood amino acids throughout the workout and after. Or, if you choose, consuming protein immediately post workout will accomplish the same goal, just on the back end. So, muscle protein synthesis will increase and proteolysis will decrease – the perfect scenario.
However, if the total protein for the day is not adequate for your goals and activity, then proteolysis will not be knocked down sufficiently to see the best results – hence why some studies show improvements to taking advantage of the most critical period (anabolic window) post workout, where protein timing is the most important, but not the only relevant point of emphasis. In this way, we need protein around our workout (within reason), as well as total protein to be met for the day (like an acute and chronic effect).