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Protein Timing and the Anabolic Window: What the Evidence Shows

10 min read

You finish your last set and reach for a shaker before your heart rate settles, because you have heard that protein has to go in within a short window after training or the session is wasted.

This guide covers where the anabolic window idea came from, what trials comparing protein before and after training found, what the evidence says about your daily protein total, and how to set up your meals. In the research here, eating protein before or after training made little difference, and in a 2013 review total protein predicted muscle gains better than timing.

5
Trials, lasting 6 to 16 weeks, that compared protein straight before training with protein after
Casuso and Goossens 2025, Nutrients
1.6
g of protein per kg a day, the best estimate of where fat-free mass gains levelled off, likely range 1.0 to 2.2
Morton et al. 2018, 42 study groups, 723 adults
0.30
kg more fat-free mass in healthy adults who added protein supplements to 6 weeks or more of resistance training
Morton et al. 2018, 49 trials, 1,863 adults
23
Trials in a 2013 timing review, where timing showed no significant effect once total protein and other factors were allowed for
Schoenfeld et al. 2013, muscle size analysis
Sources: Casuso and Goossens 2025, Nutrients. Morton et al. 2018, British Journal of Sports Medicine. Schoenfeld et al. 2013, Journal of the International Society of Sports Nutrition.

Where the anabolic window idea came from

A 2013 review by Alan Aragon and Brad Schoenfeld describes the idea. Nutrient timing means eating protein and carbohydrate in and around a training session. Some researchers referred to an anabolic window of opportunity, a limited time after training to get the most from your session. The review notes that some people even argued timing mattered more than how much you eat across the day.

The problem is the jump from short lab measurements to long-term results. Muscle protein synthesis, the rate at which your body builds muscle protein, is measured over a few hours after a meal. Aragon and Schoenfeld note that these short-term measures do not necessarily predict long-term muscle growth, which takes weeks of training. To test the window, you need trials that run for weeks and measure muscle and strength.

What the timing trials show

A 2025 review by Rafael Casuso and Lennert Goossens in Nutrients included only randomised trials that gave one group protein straight before each session and another group protein after, with training at least twice a week for at least 4 weeks. Five trials qualified, lasting between 6 and 16 weeks. Three were in untrained older adults or sedentary adults with type 2 diabetes, and two were in young trained adults. Doses were between 21g and 27g of protein, or 0.3g per kg in one trial. In all but one trial, protein came straight before or straight after the session. The other trial compared straight before with 2 hours after. Both groups in every trial ate protein within about 2 hours of training, so the trials did not test longer gaps or skipping protein.

Lean body mass, your weight minus your fat, did not differ between before and after. For chest press strength there was no difference either. The authors rated their confidence in these results as low. For leg press strength, protein before training gave a larger gain, with an effect size of 0.70, a measure of how far apart the groups ended up, where 0.5 is usually called moderate. That result narrowly reached significance, meaning it was unlikely to be due to chance, but it came from only 2 trials with 53 adults, and the authors rated their confidence in it as very low. A test of whether leg and chest results differed was not significant. The authors concluded that the timing of protein, within the window from 15 minutes before to about 2 hours after training, did not significantly affect strength or body composition, and that protein before training might help leg strength.

Protein before versus after training Effect size with 95% confidence interval. Right of zero favours protein before. Leg press strength 0.70 Chest press strength 0.07 Lean body mass -0.08 -0.5 0 0.5 1.0 1.5
Source: Casuso and Goossens 2025, Nutrients. Chest press and lean mass: 5 trials. Leg press: 2 trials, 53 adults. Dots are effect sizes. Lines are 95% confidence intervals, the likely range of the true effect. Only the leg press result reached significance, and narrowly.

This fits an earlier review. In 2013, Brad Schoenfeld, Alan Aragon and James Krieger pooled randomised trials of protein timing, with 23 trials in the muscle size analysis and 20 in the strength analysis. A simple pooled analysis showed a small to moderate effect of timing on muscle size and no significant effect on strength. Once the analysis allowed for other factors, timing showed no significant effect on either. Total protein intake was the strongest predictor of the muscle size results. The authors concluded that current evidence does not support the claim that eating protein within an hour of training significantly improves strength or muscle gains.

What the evidence says about daily protein

A 2018 review by Robert Morton and colleagues in the British Journal of Sports Medicine pooled 49 trials with 1,863 adults, average age 35, who did resistance training for at least 6 weeks. Protein supplements on top of training increased fat-free mass, everything in your body except fat, by 0.30kg, and one-rep max strength, the heaviest weight you can lift once, by 2.49kg more than training alone. The benefit for fat-free mass was smaller in older adults and larger in people who were already trained.

In a subset of 42 study groups with 723 adults, gains in fat-free mass appeared to level off at a total intake of about 1.62g of protein per kg of body weight a day. The likely range for that point ran from 1.03g to 2.20g per kg, and the authors noted the analysis was not statistically significant. Because of that range, Morton and colleagues suggested about 2.2g per kg a day for people who want the most muscle gain. In our view, about 1.6g per kg a day is a sensible starting target for most people who lift.

For an 80kg adult, 1.6g per kg comes to about 130g of protein a day. Aragon and Schoenfeld suggest 0.4g to 0.5g of protein per kg of lean body mass in the meals before and after training, and note that in short lab studies the largest response came from 20g to 40g of protein in one sitting. The reviews here did not test meal size over weeks of training. Morton and colleagues cite an analysis suggesting older adults need more protein per meal, about 0.4g per kg of body weight against 0.24g in younger adults. In our view, divide your daily total by the number of meals you eat: for 130g, that is about 33g across four meals or about 43g across three.

When timing might still matter

The guidance here comes from Aragon and Schoenfeld's 2013 review, not from long-term trials. They suggest keeping the meals before and after training no more than 3 or 4 hours apart, and say a case can be made for 5 or 6 hours with large mixed meals. If you ate a protein meal an hour or two before training, they say your next protein meal, straight after or an hour or two later, is likely enough. If your last meal was between 4 and 6 hours before training, they write that the gap justifies eating soon after. If you train after an overnight fast, they say eating protein and carbohydrate soon after makes sense, to build muscle protein and limit its breakdown.

How to put it into practice

These steps are ours, built from the reviews above.

1
Set a daily target
Aim for about 1.6g of protein per kg of body weight a day if you train for muscle or strength. For an 80kg adult, that is about 130g.
2
Split it across meals
Divide your daily total by the number of meals you eat. For 130g, that is about 33g across four meals or about 43g across three.
3
Eat within a few hours of training
Keep the meals before and after training no more than 3 or 4 hours apart, as Aragon and Schoenfeld suggest. If you train fasted, eat soon after the session.
4
Use whole foods first
In our view, chicken, fish, eggs, dairy, beans and lentils cover most needs. A shake is a convenient option when whole food is not to hand. The reviews here did not compare food sources.

Common mistakes

These are our views, based on the reviews above.

  • Timing the shake to the minute while falling well short of your daily total. In the 2013 review, total protein predicted muscle size results better than timing.
  • Eating one large protein meal and little protein for the rest of the day. Spreading protein across meals is an easy way to reach the total.
  • Treating a shake as essential. It is convenient, but a meal with chicken, fish, eggs or a large serving of beans or lentils gives a similar amount of protein.

Frequently asked questions

Is the anabolic window real?
The idea that you must eat protein within an hour of training is not supported by the 2013 review. In the 2025 review, whether protein came before or after training, within the window from 15 minutes before to about 2 hours after, made no significant difference to lean mass or chest press strength. Those trials did not test longer gaps.
How much protein should I eat per day?
In the 2018 review, gains in fat-free mass appeared to level off at about 1.62g per kg a day, with a likely range of 1.03g to 2.20g, though the authors noted this was not statistically significant. In our view, about 1.6g per kg is a sensible start, and the authors suggest about 2.2g per kg to get the most muscle gain.
Do I need a shake right after lifting?
No. If you ate a protein meal an hour or two before training, Aragon and Schoenfeld say your next protein meal, straight after or an hour or two later, is likely enough. A shake is a convenience.
What if I train fasted in the morning?
After an overnight fast, Aragon and Schoenfeld say eating protein and carbohydrate soon after training makes sense, to build muscle protein and limit its breakdown.
Is protein before training better for my legs?
In the 2025 review, protein before training gave a larger leg press gain, but the result narrowly reached significance, came from only 2 trials with 53 adults, and was rated very low certainty. The authors called for more research.

The bottom line

In trials comparing protein before and after training, the timing made little difference to lean mass or overall strength, with one borderline result favouring protein before training for leg strength. Those trials gave protein within about 2 hours of training, so they did not test longer gaps. Across 49 trials, protein supplements added muscle and strength on top of training, and in a subset of those trials, gains appeared to level off around 1.6g of protein per kg a day, though that estimate is uncertain. In our view, aim for about 1.6g per kg a day, split it evenly across your meals, and keep your meals before and after training within 3 or 4 hours of each other.

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Related reading

Sources

  • Casuso RA, Goossens L. Does Protein Ingestion Timing Affect Exercise-Induced Adaptations? A Systematic Review with Meta-Analysis. Nutrients 2025. pubmed.ncbi.nlm.nih.gov/40647175
  • Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine 2018. pubmed.ncbi.nlm.nih.gov/28698222
  • Schoenfeld BJ, Aragon AA, Krieger JW. The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. Journal of the International Society of Sports Nutrition 2013. pubmed.ncbi.nlm.nih.gov/24299050
  • Aragon AA, Schoenfeld BJ. Nutrient timing revisited: is there a post-exercise anabolic window? Journal of the International Society of Sports Nutrition 2013. pubmed.ncbi.nlm.nih.gov/23360586
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