Evidence explainerWhey protein (and other protein powders)

The Anabolic Window: A Meta-Analysis Found Total Protein Mattered More Than Timing

The 30-minute post-workout shake is gym folklore. Trials that controlled for total protein found no extra benefit from timing, though protein before bed has one intriguing trial behind it.

By Kymata Health editorial teamPublished October 9, 2026Last reviewed October 9, 2026

Medical review pending. Written by our editorial team from the studies cited below; a credentialed clinician has not reviewed it yet. Educational only, not medical advice.

Key takeaways

  • In a meta-analysis of 23 trials, protein taken in and around training did not change strength or muscle gains once total protein intake was accounted for [2].
  • Total protein intake was the strongest predictor of muscle growth [2].
  • ODS describes the window when protein supports muscle repair after exercise as lasting up to 24 hours [1].
  • One 12-week trial in 44 young men found larger strength and muscle gains with 27.5 g of protein before sleep than with a calorie-free placebo [3].
  • Whey and soy produced similar gains in long-term trials [4].

Safety at a glance

From our Whey protein (and other protein powders) monograph. Published interactions and cautions only, each with its source.

Who should be careful

  • High intakes. No UL exists for protein, but the Food and Nutrition Board advises caution with high intakes from foods and supplements combined. In healthy adults, diets of two to three times the RDA did not appear to harm kidney function or bone health (ODS). A systematic review linked chronic, excessive whey use to kidney and liver effects.[1][10]
  • Milk-derived products. Whey and casein are proteins isolated from milk (ODS); check the label if you avoid milk products.[1]
  • Before you start. Talk to your pharmacist or clinician before adding this supplement, especially if you take prescription medicines, are pregnant or breastfeeding, or have a chronic health condition.[1]

Full Whey protein (and other protein powders) safety section

The evidence, graded

Pulled from our monograph evidence tables. Grades follow our evidence-grading policy.

  • No effectNo effectProtein timed around workouts vs other timesWhey protein (and other protein powders) · Meta-analysis · n=525 · 2013 · PMID 24299050After adjusting for covariates, protein taken in and around training did not change strength or muscle-size gains versus control; total protein intake was the strongest predictor of hypertrophy.
  • Grade DImprovedProtein before sleep during a 12-week training programWhey protein (and other protein powders) · RCT · n=44 · 2015 · PMID 25926415Strength gains (+164 vs +130 kg on one-rep-max testing) and quadriceps cross-sectional area gains (+8.4 vs +4.8 cm²) were larger with protein than placebo.
  • Grade BNo effectSoy versus animal protein (including whey): strength and lean mass gainsWhey protein (and other protein powders) · Meta-analysis · n=266 · 2018 · PMID 29722584Strength rose with both soy and whey, with no difference between them; lean mass gains also did not differ between soy and other proteins.

Where the window idea comes from

Exercise breaks down muscle protein, and muscle protein synthesis rises for up to a day or two afterwards [1]. Protein timing tries to exploit that by drinking protein in and around the session [2]. The question is whether it changes results over weeks of training.

What 23 trials found

A 2013 meta-regression pooled randomized trials of protein timing: 20 studies and 478 people for strength, 23 studies and 525 people for muscle size [2]. A simple pooled analysis showed a small to moderate effect on muscle size and none on strength [2].

Once the model controlled for other factors, timing made no significant difference to strength or size [2]. Total protein intake was the strongest predictor of muscle growth, and the authors concluded that eating enough protein alongside training is the key factor [2].

How long the window lasts

ODS notes that muscle protein synthesis appears optimal with high-quality protein (about 10 g of essential amino acids) within 0 to 2 hours after exercise, but also that a meta-analysis found protein within an hour before or after exercise did not significantly increase strength or size [1]. It describes the period of anabolic opportunity as lasting up to 24 hours [1].

In practice, sports nutrition groups suggest about 0.3 g/kg of protein after exercise and then every 3 to 5 hours, which spreads intake across the day rather than racing a clock [1]. How much in total matters more; see how much protein builds muscle.

Protein before bed

In a 2015 trial, 44 young men did 12 weeks of resistance training and drank either 27.5 g of protein with 15 g of carbohydrate every night before sleep or a calorie-free placebo [3]. Strength rose more with protein (+164 vs +130 kg on one-rep-max testing), as did quadriceps size (+8.4 vs +4.8 cm²) [3].

The placebo had no calories, so the protein group also ate more protein and energy overall. That makes it hard to credit bedtime timing itself; we grade it D. ODS notes these bedtime studies used casein, a slower-digesting milk protein [1].

Does the type of protein change the answer?

Whey digests faster than casein [1]. Over 6 weeks or longer, though, a meta-analysis of 9 trials (266 people) found soy and animal proteins, including whey, gave similar gains in strength and lean mass [4]. ODS adds that soy lacks methionine and rice lacks isoleucine, which is why many products blend sources [1].

Quick answers

Do I need a protein shake right after a workout?

Trials that accounted for total protein found no added benefit from timing protein around training [2]. ODS describes the useful window as lasting up to 24 hours [1].

Is casein better before bed?

The bedtime studies cited by ODS used casein, which digests slowly [1]. No trial in our sources compared casein with whey at bedtime.

Does a shake before a workout work as well as after?

A meta-analysis found protein taken within an hour before or after exercise did not significantly increase strength or size [1].

Keep reading

Full monographs

Related articles

Browse the full Supplement & Nutrient Encyclopedia or all supplement articles.

References

  1. [1]Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2024.
  2. [2]The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. J Int Soc Sports Nutr, 2013. PMID 24299050
  3. [3]Protein Ingestion before Sleep Increases Muscle Mass and Strength Gains during Prolonged Resistance-Type Exercise Training in Healthy Young Men. J Nutr, 2015. PMID 25926415
  4. [4]No Difference Between the Effects of Supplementing With Soy Protein Versus Animal Protein on Gains in Muscle Mass and Strength in Response to Resistance Exercise. Int J Sport Nutr Exerc Metab, 2018. PMID 29722584

Whey protein (and other protein powders) and other dietary supplements are not intended to diagnose, treat, cure or prevent any disease, and these statements have not been evaluated by the FDA. Talk to your clinician or pharmacist before starting a supplement, especially if you take prescription medicines. This page has no product or affiliate links.