Supplements: Protein Supplements — Whey vs Casein vs Plant Sources
Whey protein absorption rate is ~8–10g/hr vs casein's ~6g/hr; soy ~3.9g/hr. Leucine threshold for maximal muscle protein synthesis is ~3g per serving. Food vs powder is bioequivalent when leucine-matched — powder is a delivery convenience, not a superior anabolic signal.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| Evidence Tier | 1 | tier | Tier 1 — protein supplementation and muscle protein synthesis are among the most replicated findings in nutrition science |
| Whey Absorption Rate | 8–10 | g/hour | Whey is a 'fast' protein — rapidly digested, rapid plasma amino acid peak, ideal post-exercise or between meals |
| Casein Absorption Rate | ~6 | g/hour | Casein is a 'slow' protein — forms a gel in the stomach, slow amino acid release over 5–7 hours |
| Soy Protein Absorption Rate | ~3.9 | g/hour | Soy digestion is slower than whey but faster than casein; bioavailability is high among plant proteins |
| Leucine Threshold for MPS | ~3 | g per serving | ~3g leucine per meal is required to maximally stimulate muscle protein synthesis; more has no additional anabolic effect |
| Whey Leucine per 30g Serving | 2.5–3 | g | Whey isolate at 30g protein yields ~2.5–3g leucine — near the MPS threshold per serving |
| Protein Supplementation Effect on LBM | +0.3 kg | kg lean mass | Morton 2018 meta-analysis: protein supplementation added ~0.3kg additional lean mass over resistance training alone |
Protein Sources: A Direct Comparison
Protein supplementation is the most commoditized category in sports nutrition. Understanding differences between sources requires looking at absorption kinetics, amino acid profiles, and real-world cost per effective dose.
| Protein Source | Protein % (of product) | Leucine per 30g Protein | Absorption Rate | Biological Value (DIAAS) | Cost per 30g Protein (est.) | Best Use |
|---|---|---|---|---|---|---|
| Whey Concentrate | 70–80% | 2.5–2.8g | Fast (~8–10g/hr) | ~1.09 | $0.50–0.90 | Post-workout, between meals; budget-friendly |
| Whey Isolate | 90–95% | 2.7–3.0g | Fast (~8–10g/hr) | ~1.25 | $0.80–1.40 | Post-workout, lactose-sensitive individuals |
| Casein (micellar) | 80–85% | 2.2–2.4g | Slow (~6g/hr) | ~1.01 | $0.90–1.50 | Pre-sleep, prolonged periods without meals |
| Soy Isolate | 85–92% | 2.0–2.2g | Moderate (~3.9g/hr) | ~0.91 | $0.60–1.00 | Vegan; best single-source plant protein |
| Pea Protein | 80–85% | 1.7–1.9g | Moderate (~3.5g/hr) | ~0.82 | $0.70–1.20 | Vegan; blend with rice for amino completeness |
| Rice Protein | 75–80% | 1.5–1.7g | Moderate | ~0.59 | $0.50–0.90 | Best in combination (pea+rice 70:30 blend) |
| Egg White | 80–85% | 2.8–3.2g | Moderate (~3.5g/hr) | ~1.18 | $1.20–2.00 | High leucine plant-free option; low fat |
Fast vs Slow Proteins: The Boirie 1997 Model
Boirie et al. (1997, PNAS) established the fast/slow protein framework. Whey produces a rapid, large spike in plasma amino acids peaking at ~60–90 minutes. Casein produces a modest, sustained elevation lasting 5–7 hours. Whey’s rapid kinetics produce a larger acute MPS stimulus; casein’s sustained profile may reduce muscle protein breakdown over longer periods.
The practical relevance: for most individuals eating 4+ meals per day with adequate protein at each, the fast/slow distinction is minor. It becomes relevant at meal frequencies below 3/day, during overnight fasting (casein before sleep), or during extended fasting periods.
The Leucine Threshold in Practice
For maximum MPS per meal, approximately 3g leucine is needed. This means:
- Whey: ~30–35g of protein per serving (achievable with 1 standard scoop of whey isolate)
- Casein: ~35–40g of protein per serving
- Pea protein: ~45–55g of protein per serving
- Rice protein: ~55–65g of protein per serving (major cost and volume issue)
Increasing protein beyond what’s needed to hit ~3g leucine does not further increase MPS acutely — it’s simply oxidized. This is why leucine-enriched plant protein blends can be equivalent to whey at matched leucine doses, despite lower DIAAS scores for individual plant proteins.
Related Pages
Sources
- Boirie Y et al. (1997). Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci 94(26):14930–14935.
- van Vliet S et al. (2015). The skeletal muscle anabolic response to plant- versus animal-based protein consumption. J Nutr 145(9):1981–1991.
- Morton RW et al. (2018). 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. Br J Sports Med 52(6):376–384.
Frequently Asked Questions
Is protein powder actually necessary for muscle building?
No. Protein powder is a delivery convenience, not a superior anabolic stimulus. Morton et al. 2018 (Br J Sports Med) meta-analysis found protein supplementation adds ~0.3kg lean mass over resistance training alone — but this is the effect of *additional* protein intake, not of the supplement form. If your total daily protein (1.6–2.2g/kg body weight) and leucine per meal (~3g) are met from food, powder provides no additional benefit. Powder is useful when hitting protein targets from whole food is impractical.
Should I use whey or casein post-workout?
The 'anabolic window' is much wider than previously believed — post-exercise muscle protein synthesis elevation persists for 24–48 hours, not just 30 minutes. For most practical purposes, total daily protein and leucine per meal matter more than timing. That said, whey's rapid absorption kinetics and higher leucine content make it marginally preferable if you are specifically optimizing the immediate post-exercise period. Casein before sleep may support overnight protein synthesis — some evidence supports this, particularly in older adults.
Are plant protein supplements as effective as whey?
When leucine-matched, plant proteins are approximately equivalent for MPS stimulation in direct comparison studies. The challenge is leucine content: pea protein at 1.8g leucine per 30g requires a larger serving (~40–50g) to hit the 3g leucine threshold. Blended plant proteins (pea + rice, ratio ~70:30) provide a more complete amino acid profile than either alone. Soy is the plant protein with the highest biological value and closest to whey in leucine content and digestibility (PDCAAS and DIAAS scores).
What is DIAAS and why does it matter for protein quality?
DIAAS (Digestible Indispensable Amino Acid Score) is the current gold standard for protein quality, replacing PDCAAS. It measures digestibility at the end of the small intestine (not total digestibility) and scores against the indispensable amino acid requirements. Whey scores ~1.25 (above 1.0 is 'excellent'). Pea protein scores ~0.82 and rice ~0.59. However, in the context of mixed diets and adequate total intake, DIAAS differences become less clinically significant.