Anabolic Window Myth?

Post-Workout Meal Timing Explained By a “Nutrition Engineer”

By: Jeremy Fox, CNC, CPTPublished: March 1, 2021

You may hear conflicting advice about what and when to eat after your workout.

Some swear by chugging protein shakes immediately following training. While others shout that nutrient timing is a myth, and it doesn’t matter when you eat.

In my opinion, both sides need to take it down a notch. And that’s why I’m taking a level-headed look at the controversial post-workout anabolic window.

As an engineer, I’m trained to take experimental science and apply it to real-world solutions. In this article, I review what the science really says and help you figure out how to optimize your diet for better results.

Anabolic Window Explained

What Is The Anabolic Window?

The anabolic window is a term used in bodybuilding for the period immediately following a resistance training workout when nutrition can shift the body from a catabolic to an anabolic state. It’s theorized that consuming carbs and protein during this time is an important factor for increasing muscle size and strength.

Is The Anabolic Window Real?

Yes, the anabolic window is a real physiological effect brought about by a catabolic state. However, its relevance to you depends on several factors including your training experience and what/when you eat prior to training.

In addition, the anabolic window doesn’t slam shut 30 minutes after your workout. So you won’t lose all your gains if you fail to choke down a huge meal within minutes of your last set.

The Anabolic Window Explained

There are certain aspects of the anabolic window that are pretty well demonstrated in studies. Such as an increase in anabolic activities like insulin production and protein synthesis.

So let’s start by walking through the intermediate steps of anabolism before tackling the end result.

Anabolism Defined

Anabolism is the building up of simple molecules into more complex structures within the body. Such as amino acids building proteins (protein synthesis) and glucose being shuttled into cells (insulin response).

High-intensity exercise causes a catabolic state due to an increase of hormones that break things down. But catabolic hormones also prime your body to react to anabolic hormones.

Like a pendulum, the further the weight swings in one direction, the further it will swing back in the opposite direction. And after a while, the pendulum stops in the middle.

Anabolic Window Pendulum Effect

Figure 1: Our bodies swing between catabolic and anabolic states based on our diet and exercise routines.

The Catabolic State

Certain actions cause your body’s pendulum to swing towards the catabolic side. Some of the most catabolic actions include fasting, low carb intake, and vigorous exercise (>70% max heart rate).

During intense exercise, your body releases a catabolic hormone called glucagon. This hormone is responsible for breaking down glycogen and amino acids to make glucose, a simple sugar that gets burned during exercise.

High glucagon levels also stimulate the production of an anabolic hormone called insulin1. But you have to take another action to swing the pendulum from the catabolic side to the anabolic side.

Anabolic Window

Figure 2: When catabolic hormones like glucagon are high, your body is more sensitive to anabolic hormones. Note, you don’t have to work out for 90 minutes to create an anabolic window. Adapted from Horton et al2.

The Anabolic State

After exercise, your muscles are extra sensitive to the anabolic effects of insulin for up to 2 hours3. But the longer you wait, the less the pendulum swings towards the anabolic side.

Step 1: Insulin Production

Insulin production depends on the amount of glucose in your bloodstream (aka blood sugar). Consuming high glycemic carbs after your workout is the fastest way to raise blood sugar and thereby insulin.

Also, studies show that combining carbs with protein raises insulin even more than carbs alone4.

Anabolic Window Insulin Response

Figure 3: Insulin response to various nutrients in the anabolic window. Adapted from Zawadzki et al.

This is important because insulin inhibits protein breakdown, which increases anabolism. However, spiking insulin does not necessarily build muscle.

For that, you also have to increase protein synthesis.

Step 2: Protein Synthesis

Protein synthesis is simply the building of proteins from amino acids. When your body builds more protein than it breaks down, this is called a positive protein balance and it is necessary for muscle growth.

The best way to maintain a positive protein balance is by eating enough protein throughout the day. In addition, consuming protein immediately after exercise has been shown to increase protein synthesis5.

Anabolic Window Protein Synthesis

Figure 4: Protein dynamics of protein and carbs during the anabolic window. Adapted from Levenhagen et al.

Step 3: Muscle Gain?

As you can see, intense workouts create a temporary increase in sensitivity to anabolic hormones like insulin. And consuming a mixture of carbs and protein after your workout spikes insulin while increasing protein synthesis.

However, increased insulin response and protein synthesis are only stepping stones to the ultimate goal of building more muscle. And it’s the final step where studies are more open to interpretation.

Does The Anabolic Window Matter For Muscle Gain?

Over the years there have been dozens of studies aimed at quantifying the muscle-building effect of post-workout nutrition, with varying results.

To make sense of all that data, it helps to group similar studies together and analyze their results. This is called a meta-analysis and it’s basically a study of the studies.

A Review Of Relevant Studies

In 2013, a meta-analysis compared 23 studies to figure out the effect of protein timing on muscle growth.

After their review, the researchers concluded that protein timing did not appear to significantly enhance muscle gains6. And they found that what actually accounted for any increases in muscle gain was a higher total daily protein intake.

Many in the fitness industry reference this meta-analysis when they claim that the anabolic window is a myth. And, at first glance, it seems like the case is closed.

However, I reviewed all 23 studies in the meta-analysis and I don’t think it’s logical to write off the anabolic window that quickly. The reason is that there are several problems and inconsistencies in the various studies involved.

Problems & Inconsistencies
  • 20 of 23 studies did not hold macros or calorie intake constant between groups

    This is a big oversight because any effect (or lack of effect) could be due to differences in macronutrient ratio or energy balance.

  • 19 of 23 studies used participants with no weight lifting experience

    It’s well known that muscle gain happens much easier when you’re new to resistance training. Novice lifters can make gains even without optimized nutrition. So they don’t make ideal subjects for a study about muscle gain.

  • 18 of 23 studies used young participants (typically college-aged)

    As with inexperienced trainers, it’s easier to gain muscle when you’re in your 20’s. So the anabolic window might not show up as significant in a study of younger people.

  • 13 of 23 studies did not include carbs along with protein after workouts

    Protein on its own can increase anabolism. But not to the same extent as when it’s combined with carbs. So a study that doesn’t have both carbs and protein probably won’t induce the effect of the anabolic window.

  • 7 of 23 studies used limited workout routines

    Several of the studies had participants do just one exercise, like leg extensions. While others performed only bodyweight exercises. This lack of exercise intensity might not create the catabolic environment needed to increase anabolism after the workout.

To add to these issues, the nutrient timing protocol was different between each of the studies. In fact, the researchers acknowledged that inconsistencies in the way the studies were designed made it difficult to draw any firm conclusions7.

In the end, researchers said “we must acknowledge the possibility that protein timing was, in fact, responsible for producing a positive effect”7. And even recommend consuming protein within 90 minutes after a workout to maximize the anabolic effect.

But if the anabolic window does matter, why is it so difficult to prove with studies? To understand this, we have to visualize how it compares to other diet and lifestyle factors.

Anabolic Window vs Other Factors

There are dozens of factors involved in the process of changing your body composition. Such as calorie balance, workout routine, food choices, macronutrient ratios, sleep quality, and stress level to name a few.

Compared to things like calorie balance and exercise, the anabolic window (meal timing) plays a smaller role. And it only becomes noticeable when the bigger factors are optimized.

Anabolic Window Factors

Figure 5: Relative effect of various diet & lifestyle factors on body composition (estimated).

It’s likely that the anabolic window only contributes 5-10% towards changes in body composition. While that may not sound like much, it could be the difference between a plateau and progress.

This means it’s not surprising that studies which don’t control variables like calorie intake are not able to see the effect of the anabolic window. However, there was one study in the meta-analysis that did control the big factors.

In this study, one group of trained bodybuilders consumed a protein and carb shake before and immediately after their workout. While the other group consumed the same shakes in the morning and evening, not around their workout.

Calorie intake and macronutrient ratios were matched between groups. Yet, the anabolic window group gained 6.2 lbs of muscle in 10 weeks while the control group only gained 3.3 lbs8.

Anabolic Window Body Composition

Figure 6: Effect of protein & carbs during the anabolic window for experienced bodybuilders. Adapted from Cribb et al.

This goes to show that the anabolic window does matter for experienced lifters when they consume carbs and protein. Particularly if they don’t eat within a couple of hours before the workout.

Still, there aren’t many studies that show this kind of result. So we have to combine experiments with experience to make informed decisions.

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Anabolic Window Field Observations

During my engineering career, I conducted experiments on multi-million dollar machines to figure out how to make them run more efficiently. But there were times when I couldn’t get definitive answers from my studies.

That’s why I talked to the person that ran the machine every day. An experienced technician knows how to turn the knobs to make the machine run well.

Similarly, bodybuilders are some of the most experienced technicians of the human body. They know how to “turn the knobs” of diet and lifestyle to produce an amazing physique.

Therefore, we can learn from what successful bodybuilders do. As a fitness athlete myself, I’ve seen that at least 90% of elite bodybuilders eat protein and carbs after their workouts. Especially when their goal is to gain muscle.

Of course, this speculation is often referred to as “bro-science”. And it doesn’t stand up on its own as proof that the anabolic window matters for everyone. But it’s worth keeping in mind until the science catches up.

Key Takeaways

  • The anabolic window is a period immediately following a resistance training workout when nutrition can shift the body from a catabolic to an anabolic state
  • It’s not as short as previously thought, lasting anywhere from 45 to 90 minutes depending on exercise intensity and duration
  • Calorie balance and total daily protein intake matter more than the anabolic window
  • The anabolic window becomes more critical if you haven’t eaten for more than 2 hours prior to your workout
  • It’s likely not significant for younger people or those just starting resistance training but becomes important as you gain experience


When your goal is muscle gain, the first things you must do are work out hard and eat enough calories and protein. Once you do that, you will likely see a benefit if you consume carbs and protein after your workouts.

In addition, the anabolic window becomes more important as you get older and get used to the stress of resistance training. For more meal timing tips, check out some of my related articles below!

1) Samols, Ellis, Germano Marri, and Vincent Marks. “Interrelationship of glucagon, insulin and glucose: the insulinogenic effect of glucagon.” Diabetes 15.12 (1966): 855-866.
2) Horton, Tracy J., et al. “Glucose kinetics differ between women and men, during and after exercise.” Journal of applied physiology 100.6 (2006): 1883-1894.
3) Holloszy, John O. “Exercise-induced increase in muscle insulin sensitivity.” Journal of applied physiology (2005).
4)Zawadzki, K. M., B. B. Yaspelkis 3rd, and J. L. Ivy. “Carbohydrate-protein complex increases the rate of muscle glycogen storage after exercise.” Journal of Applied Physiology 72.5 (1992): 1854-1859.
5) Levenhagen, Deanna K., et al. “Postexercise nutrient intake timing in humans is critical to recovery of leg glucose and protein homeostasis.” American Journal of Physiology-Endocrinology And Metabolism 280.6 (2001): E982-E993.
6) Schoenfeld, Brad Jon, Alan Albert Aragon, and James W. Krieger. “The effect of protein timing on muscle strength and hypertrophy: a meta-analysis.” Journal of the International Society of Sports Nutrition 10.1 (2013): 1-13.
7) Aragon, Alan Albert, and Brad Jon Schoenfeld. “Nutrient timing revisited: is there a post-exercise anabolic window?.” Journal of the international society of sports nutrition 10.1 (2013): 1-11.
8) Cribb, Paul J., and Alan Hayes. “Effects of supplement timing and resistance exercise on skeletal muscle hypertrophy.” Medicine & Science in Sports & Exercise 38.11 (2006): 1918-1925.

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