Whey vs Casein: An Evidence-Based Comparison
Both come from milk, but they behave like two completely different proteins in the body. Here's how whey and casein compare on absorption speed, leucine content, muscle protein synthesis, body composition outcomes, and when to actually use each.
Last reviewed June 28, 2026 · Reviewed by the SuppIndex research team (editorial policy) · Educational only — not medical advice.
The 30-second answer
- Speed: Whey peaks plasma amino acids in 60–90 minutes; casein releases over 6–8 hours.
- MPS: Whey wins acutely post-workout; casein wins overnight and between meals.
- Leucine: Whey ~11% vs casein ~9% — whey produces a larger leucine peak.
- Verdict: Use whey post-workout, casein pre-sleep. Total daily protein matters more than which type you choose.
Side-by-side comparison
| Whey Isolate | Micellar Casein | |
|---|---|---|
| Source | Cheese-making byproduct, ultrafiltered | Native milk protein, microfiltered |
| Protein content | ≥90% by weight | ~85% by weight |
| Leucine content | ~11% of total AAs | ~9% of total AAs |
| Time to peak plasma amino acids | 60–90 minutes | 3–4 hours |
| Duration of aminoacidaemia | ~2–3 hours | 6–8 hours |
| Acute MPS response | Higher peak (better post-workout) | Lower peak, longer duration |
| Suppression of breakdown | Minimal | Strong (anti-catabolic) |
| Best use | Post-workout, fast MPS | Pre-sleep, between meals |
| Typical effective dose | 20–40 g per serving | 30–40 g per serving |
| DIAAS | ~1.09 | ~1.18 |
| Lactose | < 1% (well tolerated) | ~1% (well tolerated) |
| Cost (typical) | Mid–high | Mid–high |
The landmark trials
The defining work on whey vs casein kinetics is Boirie, Dangin & Beaufrère (1997), which coined the "fast vs slow" protein framework. They demonstrated that whey produced a rapid, transient aminoacidaemia and high acute MPS, while casein produced a flatter but more prolonged amino acid curve and better whole-body protein balance over the full 7-hour postprandial period.
The practical follow-up came with Res et al. (2012), which showed 40 g of pre-sleep micellar casein raised overnight whole-body protein synthesis by ~22% vs placebo, and Snijders et al. (2015), which translated this into 12-week training adaptations: pre-sleep casein groups gained significantly more muscle mass and 1RM strength than placebo.
For post-workout, Tang et al. (2009) directly compared whey hydrolysate, casein and soy at matched leucine intake — whey produced significantly greater mixed-muscle MPS than casein at rest and after resistance exercise.
Pick whey if…
- You want the fastest post-workout MPS spike
- You train multiple times per day
- You're cutting and want low fat/lactose with maximum leucine
- You need a fast, easy-to-mix shake
Pick casein if…
- You want overnight MPS while you sleep
- You have long gaps between meals
- You're older and benefit from anti-catabolic protection
- You want a more filling, satiating protein
Explore further on SuppIndex
- Whey Protein Isolate ingredient page → full evidence score, dosing, safety, linked studies
- Whey Protein Concentrate (WPC 80) →
- Hydrolysed Whey Protein →
- Micellar Casein →
- Browse all proteins →
This article is for educational purposes only and is not medical or dietetic advice. Total daily protein intake matters far more than which type of protein you pick — speak to a registered dietitian for personalised targets.