Casein, whey and soy protein effects on muscle building in young men
What it found
In young men, casein led to less new muscle protein being made than whey or soy, both at rest and after leg exercise.
Whey raised blood amino acid levels more than casein or soy.
What they found
Studies in people
Blood amino acid levels
Whey raised blood levels of essential amino acids, branched-chain amino acids, and leucine more than casein or soy did in these young men.
Muscle building at rest
At rest, the rate of new muscle protein made was lowest with casein. Whey led to about 93% more muscle protein being made than casein, and soy led to 64% more than casein.
Muscle building after exercise
After leg exercise, whey led to about 122% more muscle protein being made than casein. Soy led to 69% more than casein. Whey also beat soy by 31%.
What the authors conclude
- They conclude that whey and soy lead to more muscle protein being made than casein in young men, both at rest and after exercise.
- They note that whey worked better than soy after exercise, even though both are digested quickly.
- They suggest these differences might come down to digestion speed or small variations in leucine content.
How it was done
The authors wanted to compare how fast-digested proteins like whey and soy stack up against a slow-digested one, micellar casein, for building muscle. They looked at this both during rest and after resistance exercise.
Eighteen healthy young men were split into three groups of six. Each group did a one-legged resistance workout and then drank a beverage with 10 g of essential amino acids from either whey, casein, or soy. Researchers measured how much new muscle protein was made using a labelled amino acid tracer.
What it can’t tell you
- We summarised it from the abstract only.
- This was a single session with only 18 men, so it cannot show what happens over weeks or months of training.
- It only tested young men, so the results may not apply to women or older adults.
Who paid
- Authors work at
- McMaster University, Canada
The paper
- Title
- Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men
- Type
- Study
- Evidence
- Studies in people
- Summarised from
- Abstract only
- Cite
- Tang JE, Moore DR, Kujbida GW, Tarnopolsky MA, Phillips SM (2009). Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. Journal of applied physiology (Bethesda, Md.. doi:10.1152/japplphysiol.00076.2009PubMed 19589961DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error