A bedtime shake worked at 40 g and did nothing at 30 g
40 g at bedtime raised overnight muscle protein building in young men and in men averaging 72. 30 g reached the muscle but left that rate level with placebo.
What the study found
Forty grams before sleep worked; thirty grams did not
Forty grams of casein at bedtime raised the rate at which muscle protein was built overnight, in young men after training and in men averaging seventy-two. Thirty grams, in the largest of the three trials, reached muscle but left that rate level with placebo. Added leucine did not help.
The caveat · One night's rate, not muscle kept
These measure a building rate across one night, not muscle retained across a training block. The forty-gram result in older men reached p = 0.02, and its supporting tracer analysis only p = 0.08. The founding study's clearly significant effects were whole-body, which includes gut and liver protein, not muscle specifically. Young men in two of the three trials, older men in the other, no women anywhere.
What we don't know
The trials for and against bedtime protein came from one laboratory, so dose likely explains the split: the effect appears somewhere between 30 and 40 g. Where exactly, and whether any muscle is kept, is untested.