Leucine switched on muscle building without adding muscle
Across nine trials in older people, leucine raised the rate of muscle protein synthesis substantially and moved lean body mass not at all.
What the study found
Leucine sped protein synthesis up and left muscle mass unchanged
Flipping the switch more often is not the same as having more to build with. Across nine trials in older people, leucine raised the rate of muscle protein synthesis substantially, 1.08 on a standardised scale, and moved lean body mass not at all, 0.18 with an interval running through zero.
The caveat · Synthesis in hours, muscle in weeks
Nine trials is a small pool and the searches ended in December 2013, so a decade of later work is missing. The two outcomes are measured on different clocks: synthesis takes hours, lean mass takes weeks to months, so part of the contrast is a contrast of study durations. Older adults only.