The 20 g ceiling is a property of how long they measured
Both studies behind that number stopped four hours after the meal. Work the whole body and 40 g beats 20 g; follow 100 g for twelve hours and it stays ahead of 25 g.
What the study found
The 20 g per-meal limit came from four-hour measurements
One of the two tracer studies that set that number had six participants. Both stopped measuring four hours after the meal, and a large dose is still digesting then. Work the whole body instead of one leg and 40 g beats 20 g; follow 100 g for twelve hours and it stays ahead of 25 g.
The caveat · Young trained men, hours not months
All four are acute tracer studies in young trained men, measuring a building rate over hours rather than muscle held onto over months, and the two do not always track. The original plateau rests on telling a 20 g response apart from a 40 g one in six people. The 100 g result comes from a four-tracer method used by very few laboratories. Nobody tested whether the same protein split across the day would do as well.
What we don't know
A 20 g per-meal ceiling shows up four hours after a one-leg session and not twelve hours after whole-body work, so it belongs to the measurement. No trial has fed large doses for months and weighed the muscle kept.