In 30 seconds
- The window exists, but it is much wider than was thought: the effect of training on muscle lasts at least 24 hours.
- In a meta-analysis of 23 trials, the advantage of taking protein right next to training disappeared once total daily protein was matched.
- The practical rule: if more than 3-4 hours have passed since your last meal, have at least 25 g of protein when you finish.
- In older people the clock may count for more: in 13 men aged 74, protein taken just after training built muscle, and protein taken 2 hours later did not.
The “anabolic window” is the idea that, once you finish training, there is a short window in which to take protein and make the most of the session. The studies say that this window exists, but that it is much wider than was thought, and that what counts most is your total protein for the day. With one nuance: in older people, the clock may matter more.
Where the idea comes from
The window hypothesis was based mainly on studies in which people trained fasted. In that situation, the muscle's amino acid balance stays negative after training, and it makes sense to take protein soon 1.
But most people do not train fasted. If you ate something 1-2 hours beforehand, that meal serves both as your pre-training meal and as your meal for immediately afterwards 1. Then the urgency disappears.
Level of evidence by outcome
| Outcome | Evidence | What the data show |
|---|---|---|
| Total daily protein is what matters | High | The effect of timing disappears when total protein is matched, across 23 hypertrophy trials. |
| Same result before or after training | Moderate | Similar results in a 10-week trial with 25 g of whey protein. |
| Good response up to 2 hours later or more | Moderate | ISSN position. The effect of training on muscle lasts at least 24 hours. |
| Servings of about 20 g every 3 hours | Preliminary | More muscle protein synthesis over 12 hours than 8 servings of 10 g or 2 of 40 g. |
| In older people, taking it straight after | Preliminary | One small trial, with 13 men aged 74, in favour of taking it within the following 5 minutes. |
| Protein before bed | Moderate | 30-40 g of casein increases muscle protein synthesis overnight, according to the ISSN. |
The rating is our own, based on the number of studies, their quality and the consistency of the results.
The key studies
| Study | Type | Sample | Outcome |
|---|---|---|---|
| Esmarck et al., 2001 | Trial | 13 men aged 74, 12 weeks | 10 g of protein just after training: 7% more quadriceps area. Taken 2 hours later, no change. 7 |
| Aragon and Schoenfeld, 2013 | Review | Studies on the timing of servings | The window depends on your last meal. If more than 3-4 hours have passed, it is advisable to have at least 25 g of protein when you finish. 1 |
| Schoenfeld et al., 2013 | Meta-analysis | 23 hypertrophy trials and 20 strength trials | The benefit of taking protein right next to training disappeared once total daily protein was taken into account. 2 |
| Areta et al., 2013 | Trial | 24 trained men | With 80 g of protein over 12 hours, 4 servings of 20 g every 3 hours gave 31-48% more muscle protein synthesis than 8 of 10 g or 2 of 40 g. 8 |
| Schoenfeld et al., 2017 | Trial | 21 trained men, 10 weeks | 25 g of whey protein just before or just after training: similar results in strength, muscle and fat. 3 |
| Wirth et al., 2020 | Meta-analysis | 65 trials, 2,907 adults | More lean mass with protein supplements, with no advantage for any particular timing. 6 |
| Trommelen et al., 2023 | Tracer trial | 25 g versus 100 g of protein after training | With 100 g, the anabolic response was greater and lasted more than 12 hours. 9 |
According to the ISSN
A window of hours: muscle after training
A window of hours, not minutes
The International Society of Sports Nutrition (ISSN) sums up what is known as follows 5:
- Muscle protein synthesis rises after training, peaks at about 3 hours and stays elevated for 24 to 72 hours.
- Muscle is more sensitive to protein for at least 24 hours, and probably most so in the first 5-6 hours.
- Before and after training, both options have benefits.
In its position on meal timing, the ISSN adds that taking good-quality protein from just after training up to 2 hours later produces a good response 4.
The clock versus the daily total
One meta-analysis pooled 23 trials on muscle mass and 20 on strength. Taking protein right next to training seemed to give a little more muscle, but that advantage disappeared once the researchers took into account how much protein each group ate per day 2.
In the studies that did not match protein, the shake group ate more: 1.66 g per kilo a day on average, compared with 1.33 g 2. The authors conclude that the effect came from eating more protein, not from the timing 2.
A later meta-analysis, with 65 trials and 2,907 adults, confirmed that protein supplements increased lean mass without any particular timing giving better results 6.
Before or after: the direct test
In a 10-week trial, 21 trained men took 25 g of whey protein isolate just before or just after training. To make the difference clear, they ate nothing in the 3 hours on the other side of the session 3.
The result: strength, muscle thickness and body fat changed in a similar way in both groups. The authors conclude that the window is not that narrow and that you can choose the timing for convenience 3. One nuance: the participants lost fat during the study, so the results fit best with phases of calorie deficit 3.
It all depends on your last meal
The review by Aragon and Schoenfeld turns this into simple rules 1:
- Good-quality protein before and after, about 0.4-0.5 g per kilo of lean mass at each meal. With 70 kg of lean mass, 28-35 g.
- No more than 3-4 hours between your meal before and your meal after, for a 45-90 minute session. If they are large, mixed meals, the margin can stretch to 5-6 hours.
- If you train after more than 3-4 hours without eating, have at least 25 g of protein as soon as you finish.
What about carbohydrates? According to the same review, if you train once a day, replenishing glycogen quickly is not urgent: it recovers in less than 24 hours 1. The ISSN reserves rapid refuelling, with 1.2 g of carbohydrate per kilo per hour, for when there are less than 4 hours between two sessions 4.
Trial with 24 men
Spreading your protein counts too
How to spread protein over the day
If the exact timing matters little, the distribution matters a bit more. In a trial with 24 trained men, all of them took 80 g of whey protein over the 12 hours after training, split in three ways 8:
- 8 servings of 10 g every hour and a half.
- 4 servings of 20 g every 3 hours.
- 2 servings of 40 g every 6 hours.
All three raised muscle protein synthesis, but splitting it into 4 servings of 20 g gave 31-48% more than the other two 8. Along the same lines, the ISSN recommends servings of 20-40 g every 3-4 hours 4.
Is there a ceiling per serving? For years it was said that anything above 20-25 g was wasted. A 2023 study calls this into question: after training, 100 g of protein gave a greater and longer anabolic response, lasting more than 12 hours, than 25 g 9. Large servings count too.
Men aged 74, 12 weeks
In older people: straight after or 2 hours later
In older people, the clock matters more
Here is the exception. In one trial, 13 men aged 74 did strength training for 12 weeks. One group took a supplement with 10 g of protein within 5 minutes of each session, and the other 2 hours later 7:
- Straight after: quadriceps area increased by 7% and muscle fibre size by 22%.
- At 2 hours: no significant changes in muscle.
It is a small study with little protein, but it suggests that, with age, taking it close to training may carry more weight. We expand on this in protein in older adults: what the studies say.
And before bed
The night is a long window without food. According to the ISSN, 30-40 g of casein before bed increases muscle protein synthesis overnight. It also raises energy expenditure, without affecting fat mobilisation 5.
What to do, in short
- Prioritise the daily total: 1.4-2.0 g per kilo if you train, according to the ISSN 5. Work it out with our protein calculator.
- Spread it over 3-5 servings of 20-40 g, every 3-4 hours.
- Do not leave more than 3-4 hours between your meal before and your meal after training.
- If you train fasted or you are older, take your protein shortly after finishing.
You will find it explained in practical terms in protein before or after training.
What about our protein?
Our Gourmet Isolate Protein is whey protein isolate. Whey protein is what several of these trials used. It provides 42.8 g of protein per 50 g serving, or about 21 g with a single scoop. Protein contributes to a growth in muscle mass 10. Contains milk and soya. A varied and balanced diet and a healthy lifestyle are important.
Frequently asked questions
Does the anabolic window exist?
Yes, but it is much wider than was thought. According to the International Society of Sports Nutrition, the effect of training on muscle lasts at least 24 hours, and taking protein from just after training up to 2 hours later gives a good response.
How long does the anabolic window last?
It depends on when you ate before training. If it was 1-2 hours beforehand, that meal also covers the period immediately afterwards. If more than 3-4 hours have passed, it is advisable to have at least 25 g of protein as soon as you finish.
Is my session wasted if I do not take protein straight after?
No. In a meta-analysis of 23 trials, the advantage of taking it right next to training disappeared once total daily protein was matched. What counts most is reaching your daily figure.
How much protein can you use from one serving?
The ISSN suggests servings of 20-40 g. A 2023 study found that 100 g after training gave a greater and longer anabolic response than 25 g, so the idea of a fixed ceiling of about 20 g per serving does not hold up.
Sources
- Aragon AA, Schoenfeld BJ. Nutrient timing revisited: is there a post-exercise anabolic window? J Int Soc Sports Nutr. 2013;10:5. View publication
- Schoenfeld BJ, Aragon AA, Krieger JW. The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. J Int Soc Sports Nutr. 2013;10(1):53. View publication
- Schoenfeld BJ, Aragon A, Wilborn C, Urbina SL, Hayward SE, Krieger J. Pre- versus post-exercise protein intake has similar effects on muscular adaptations. PeerJ. 2017;5:e2825. View publication
- Kerksick CM, Arent S, Schoenfeld BJ, et al. International Society of Sports Nutrition position stand: nutrient timing. J Int Soc Sports Nutr. 2017;14:33. View publication
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20. View publication
- Wirth J, Hillesheim E, Brennan L. The role of protein intake and its timing on body composition and muscle function in healthy adults: a systematic review and meta-analysis of randomized controlled trials. J Nutr. 2020;150(6):1443-1460. View publication
- Esmarck B, Andersen JL, Olsen S, Richter EA, Mizuno M, Kjær M. Timing of postexercise protein intake is important for muscle hypertrophy with resistance training in elderly humans. J Physiol. 2001;535(1):301-311. View publication
- Areta JL, Burke LM, Ross ML, et al. Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. J Physiol. 2013;591(9):2319-2331. View publication
- Trommelen J, van Lieshout GAA, Nyakayiru J, et al. The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Rep Med. 2023;4(12):101324. View publication
- Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product.
