A Protein Source Enters the Gut
Every protein source starts the same race, from very different starting blocks.
- ~30 min: Anabolic window (post-workout timing)
- 20–40 g: Typical dose (per serving)
- <5 min: Stomach entry (after swallowing)
- ~80 µmol/L: Fasting blood AA (baseline level)
Why the source matters
Whey, casein, soy and pea digest at different speeds.
The shared starting point
All proteins begin as long folded chains of amino acids.
Enzymes Break Protein Into Peptides
Stomach acid and enzymes unfold and cut proteins into absorbable pieces.
- 1.5–3.5: Gastric pH (pepsin active range)
- 1000s: Peptide bonds cut (per protein molecule)
- 1–4 hrs: Gastric emptying (depends on source)
- 6–7: Intestinal pH (enzyme optimum zone)
Stomach breakdown
Pepsin starts unfolding and cleaving the protein chain.
Clotting changes the clock
Casein clots in the stomach, slowing its release.
Small intestine finish
Pancreatic enzymes finish cutting peptides into amino acids.
Whey Protein — Fast, Sharp, Short-Lived
Whey stays liquid in the stomach and empties into the gut quickly.
- ~45 min: Whey peak time (fastest of all sources)
- 2–3×: Leucine spike (triggers muscle synthesis)
- High: Absorption speed (fast gastric emptying)
- ~1.3 hrs: Plateau length (short, sharp curve)
Liquid, fast-emptying
Whey does not clot, so it leaves the stomach quickly.
Leucine trigger
A fast leucine spike strongly triggers muscle protein synthesis.
Casein & Plant Protein — Slow and Sustained
Casein clots and plant proteins digest slower, spreading amino acids over hours.
- ~110 min: Casein peak time (micelle clotting delay)
- ~6 hrs: Casein plateau (longest sustained release)
- 60–90 min: Soy/pea peak time (intermediate speed)
- ~3 hrs: Plant protein plateau (moderate duration)
Casein clotting
Casein forms a gel in the stomach, slowing digestion.
Plant fiber effect
Soy and pea fiber slows enzyme access to protein.
Four Curves, One Blood Amino Acid Pool
Speed and duration trade off differently for every protein source.
- ~70 min: Whey vs casein gap (peak time difference)
- ~90–100%: Total AA delivered (eventually, all sources)
- Whey: Fastest MPS trigger (best post-workout pick)
- Casein: Longest coverage (best overnight pick)
Shape over total
Curve shape matters more than total amino acids delivered.
Practical pairing
Many athletes combine fast whey with slow casein or plant.