Illustration of a muscular bodybuilder climbing through the mythical anabolic window.

The Anabolic Window: Both Fact & Fiction

The “anabolic window” is an old bodybuilding term. A few years ago, it was pilloried by the evidence-based fitness community, and perhaps rightfully so—the requirements were woefully strict.

As so often happens, the backlash was overly harsh. There’s some merit to the idea of the anabolic window. The truth is that most people can benefit from taking advantage of it. That’s even more true for naturally thinner people.

A skinny guy building muscle. Illustrated by Shane Duquette for Outlift.

What’s the Anabolic Window?

The anabolic window is the period after lifting weights when your muscles are ready to shift from breaking down muscle (a catabolic state) to building muscle (an anabolic state).

The idea is that lifting weights stimulates muscle growth and that our muscles are the hungriest for protein immediately after training. That’s true. That’s exactly what hypertrophy training does, and that’s exactly when muscle growth spikes the highest (study).

In the classic bodybuilding era, the anabolic window was thought to last for about 30 minutes after training. In the modern evidence-based era, the window is understood to last for closer to 4 hours, opening 1–2 hours before working out and staying open for 1–2 hours afterwards (study, study).

Illustration of a weight lifter climbing through the anabolic window.

Also, keep in mind that if your workouts are challenging enough, you can build muscle fairly steadily for 2–3 days after working out. It’s important to eat enough food during that entire period (study). That’s less of a window, though. More of a doorway.

The Myth of the Anabolic Window

If you browse the more archaic corners of the internet or listen to the wisdom of greying bodybuilders, you’ll hear of the awesome power of the anabolic window—of how you have 30 minutes to chug a massive post-workout shake, stimulating a huge surge of muscle growth and warding off fat gain. Some of these shakes were enormous. It wasn’t uncommon for guys to pound back over a thousand calories. (More on that in a moment.)

These old bodybuilders weren’t wrong about the benefits, but they were wrong about the timing. The anabolic window is actually quite a bit more forgiving than that. If you eat a balanced meal every few hours, you’ll have a steady supply of amino acids, carbs, and fatty acids gradually digesting while you train. There’s never any great urgency to chug a post-workout shake.

The Truth of the Anabolic Window

There’s actually quite a bit of research showing that having a protein shake after working out increases muscle growth (study, study, study, study, study). If you’re working out before breakfast, if you aren’t eating steadily throughout the day, or if you’re falling behind on calories, then the benefits are even more dramatic (study).

A study graph showing the muscle-building benefits of consuming protein powder during the anabolic window.

For example, Hulmi and colleagues gave some participants a protein shake during the anabolic window and other participants a zero-calorie placebo shake. The participants who had the protein shake gained 20% more muscle (study). After all, having a post-workout protein shake increases your protein and calorie intake, both of which improve muscle growth.

If you’re falling behind on calories, the anabolic window can be the difference between muscle loss and muscle growth. Working out can burn 300–400 calories. Most people can clamber out of that pit without much trouble, but many thinner people find themselves stuck there, especially if their workout causes them to skip or delay a meal. A thousand-calorie workout shake can bring you from a 500-calorie deficit to a 500-calorie surplus. That can save your bulk.

What to Eat During the Anabolic Window

There are two dogmas. The first dogma says to eat a balanced meal as you normally would, though perhaps somewhat larger. The second says to have a high-calorie, high-protein, high-carb, rapidly digestible post-workout shake.

Both approaches can work. It all depends on what you’re trying to do.

For Fat Loss

If you’re trying to lose fat, you’re probably struggling to control your appetite. You need to find a way to eat fewer calories more comfortably. Chugging a high-calorie shake is a poor use of your caloric budget. It’s a bad way to manage your appetite.

If you’re trying to lose fat, turn to more filling foods. Don’t chug a shake or rush home to prepare a feast. Instead, eat a balanced meal at your leisure, when you’re hungry, and never past fullness.

Make a meal that’s high in protein, rich in carbs, sufficiently fatty, and packed full of fibre. Think of meals like stir-fries, steak and potatoes, salmon with broccoli and rice, fiery chilis, and steaming stews. Add a side of green salad or fruit salad.

Illustration of man eating a filling post-workout meal to burn fat and build muscle.

For Body Recomposition

If you’re doing a recomp (aiming for simultaneous muscle growth and fat loss), you might hear of calorie cycling and carb cycling, where you eat more during the anabolic window and less on rest days. That won’t make or break your results, but it’s not a bad rule of thumb.

When you work out, you burn around 300–400 calories. You need to eat those calories back at some point. You may as well eat them during the anabolic window, ensuring you have enough nutrients available when your body is the most eager to build muscle.

If you’re a sparrowly eater or have a hummingbird’s metabolism, you might want to have a high-calorie post-workout shake or bulking smoothie after working out. If you have an over-eager appetite, a lower-calorie protein shake or balanced meal will probably serve you better.

For Muscle Growth

If you’re trying to build muscle and bulk up, the anabolic window is an opportunity to get ahead on calories. Since you’re intentionally trying to overeat, it can help to eat foods that digest quickly and easily, keeping your diet easy on your appetite.

This is where high-calorie shakes and smoothies become a godsend. I had 600–1,200 calorie shakes during my workouts when I was underweight. I would sip on them while resting between sets. I kept bringing those shakes to the gym with me until I’d gained 40 pounds. Then I eased back, switching from workout shakes to post-workout feasts.

Illustration of a man drinking a post-workout shake/smoothie to build muscle and bulk up.

How to Make a Post-Workout Shake

If you’re making a post-workout shake, you want at least one scoop of protein powder, some powdered carbs (like maltodextrin or ground oats), and maybe 5 grams of creatine. Use quantities that get you up to your calorie goals.

For a simple homemade mass gainer, you could combine 60 grams of whey, 90 grams of maltodextrin, and 5 grams of creatine. That would get you about 55 grams of protein, 95 grams of carbs, and 600 calories.

Frequently Asked Questions

Should You Have BCAAs While Working Out?

Protein gets broken down into amino acids. Those amino acids are what we use to build muscle. Different protein sources digest at different speeds, but we can skip that entire process by supplementing with amino acids directly. That’s what branched-chain amino acids (BCAAs) are for. It’s a mix of amino acids thought to be ideal for building muscle.

Historically, drinking amino acids while training seemed like a good idea. If the anabolic window is narrow, then you have only a limited opportunity to feed your muscles. The quicker a protein source digests, the faster you can flood your muscles with amino acids.

However, the anabolic window isn’t so narrow as that. You can use any protein source, with whey protein being the most popular.

Should You Have Whey Protein After Working Out?

Early research supported the idea of consuming quickly-digested protein after training, with whey protein outperforming casein (meta-analysis, study). Other papers called those findings into question, making the overall body of evidence too murky to draw any strong conclusions (study, study, study).

I think what’s happening is this: it’s crucial to consume enough protein overall, and it helps to have protein within 1–2 hours of working out, but the type of protein you consume doesn’t matter very much. So, if you want to buy a supplement, whey is the most obvious choice. But if you prefer something else, that’s fine, too.

Should You Have a Protein Shake Before or After Working Out?

It takes protein a little bit of time to be broken down into amino acids, and it takes those amino acids some time to flow into your muscles. It might make sense, then, to have a protein shake before working out.

However, there’s no great rush to feed your muscles immediately after training, especially if you ate 1–2 hours before your workout.

So, yes, you should have a protein shake before or after working out. But we can do a bit better than that:

  • If you’re working out before breakfast, have a protein shake before working out.
  • If you’re hungry while lifting, have a protein shake (or a snack).
  • If training on a full stomach feels bad, eat 2 hours before training, then have a protein shake afterwards.
  • If you’re struggling to eat enough calories to gain weight, have the protein shake before your workout. That way, you’ll be ready to eat again sooner.

Do Cardio Workouts Have an Anabolic Window?

Cardio doesn’t stimulate very much muscle growth (anabolism), so there’s no real anabolic window to speak of. You need to eat enough protein, but you don’t need to stress about the timing of it.

However, cardio is a metabolic fireplace. If you’re a 180-pound guy going rucking for 2 hours, you can burn close to 1,500 calories. That’s a devastating number of calories to lose. If you’re trying to build muscle, you need to eat back the calories you burn, lest you fall into a deficit.

You can get your calories from regular meals, from smoothies, or from post-workout shakes. If I’m doing long, sweaty cardio sessions outside, I’ll often have some Gatorade to help me keep up with calories, water, and electrolytes. Still, you might need more.


If you’re already eating every few hours, eating enough protein, and eating enough calories, then you don’t need to worry about the anabolic window. You can still have a post-workout shake, and it will still help, but not more than a meal would. Relatively few people satisfy all these requirements, though.

If you’re having trouble eating enough food to build muscle, if you’re eating less than 0.7 grams of protein per pound bodyweight per day, or if you’re falling behind on your meal schedule, then the anabolic window is a glimmering opportunity to build more muscle. Have a post-workout shake, a smoothie, or race home to prepare a grand feast. You need those nutrients. They can make all the difference.

Most regular people who lift weights can build more muscle by having a protein shake after working out. It increases their calorie and protein intake, and it satisfies the anabolic window. You could get those same benefits through your diet, but most people don’t. Having a protein shake is popular for a reason. It’s easy and it works.

Cover of our Outlift intermediate bulking program.

If you want the latest muscle-building research and methods, we have a free newsletterIf you want a full foundational bulking program, including a 5-month full-body workout routine, diet guide, recipe book, and online coaching, check out our Bony to Beastly Program (for men) or Bony to Bombshell Program (for women). If you want a customizable intermediate muscle-building program, check out our Outlift Program.

Shane Duquette is the co-founder and creative lead of Outlift, Bony to Beastly, and Bony to Bombshell, and has a degree in design from York University in Toronto, Canada. He's personally gained 65 pounds at 11% body fat and has ten years of experience helping over 10,000 skinny people bulk up.

Marco Walker-Ng is the co-founder and strength coach of Outlift, Bony to Beastly, and Bony to Bombshell, and is a certified trainer (PTS) with a Bachelor's degree in Health Sciences (BHSc) from the University of Ottawa. His specialty is helping people build muscle to improve their strength and general health, with clients including college, professional, and Olympic athletes.