Leucine is a special amino acid that turns on the body's muscle-building machine.
Scientific Claim
Leucine activates the mTORC1 signaling pathway to initiate muscle protein synthesis.
Original Statement
“Ground beef is an absolute complete protein, right? You get the full spread of essential amino acids just like you do with most animal proteins. You get leucine, which is the big switch that flips on muscle protein synthesis. And you have to think of leucine as sort of like turning the key in the ignition. Without it, muscle protein synthesis simply doesn't start.”
Context Details
Domain
nutrition
Population
human
Subject
Leucine
Action
activates
Target
mTORC1 signaling pathway to initiate muscle protein synthesis
Intervention Details
Evidence from Studies
Supporting (3)
Whey protein, which has lots of leucine, made muscles grow better than collagen protein, which has little leucine — suggesting leucine is key to starting muscle growth.
Giving leucine to premature baby pigs turned on a specific molecular chain reaction (Sestrin2 → GATOR2 → Rag → mTORC1) that made their muscles grow more protein.
Technical explanation
This paper directly demonstrates that leucine pulses activate mTORC1 via the Sestrin2-GATOR2-Rag pathway to increase protein synthesis in skeletal muscle of preterm piglets, matching the assertion exactly in mechanism and outcome.
Leucine was given to baby pigs, and it turned on a cellular switch (mTORC1) that made their muscles build more protein, proving leucine helps muscles grow through this pathway.
Technical explanation
This paper directly tests whether leucine supplementation activates mTORC1 to increase protein synthesis in skeletal muscle, showing that leucine enhances protein synthesis via mTORC1 pathways in multiple tissues, including skeletal muscle, with clear molecular markers like S6K1 and eIF phosphorylation.
Contradicting (2)
Scientists turned on a different switch (c-Myc) and muscles grew protein — even when mTORC1 was completely off. So mTORC1 isn’t the only way.
Technical explanation
This study shows protein synthesis can be increased in muscle without any mTORC1 activation via c-Myc overexpression, directly contradicting the assertion that mTORC1 is necessary for leucine-driven protein synthesis.
Even when chickens got way more leucine than needed, their muscles didn’t make more protein — so leucine doesn’t always work like we thought.
Technical explanation
This study directly tests leucine supplementation in broilers and finds no effect on protein synthesis or degradation pathways, contradicting the assertion that leucine reliably activates mTORC1 to stimulate muscle protein synthesis.