For older guys who lift weights, having a protein shake with 3 grams of leucine right after workouts and before bed doesn’t help build more muscle or strength than just having a placebo drink with...

Older guys who lift weights and take a protein shake after workouts and before bed get the same muscle-building effect as those who take a fake shake with the same calories — so the protein might not actually help at the molecular level.

If you're a young man who already lifts weights and eats enough protein, doing strength training twice a week for 12 weeks will make you stronger and build more muscle — and taking leucine supplements won't make any extra difference compared to taking a sugar pill.

If young, healthy guys lift weights for 12 weeks and drink a protein shake before bed, they get way stronger than those who don’t — like 30 more pounds on their lifts.

Older guys (60–75) who already eat enough protein don’t get stronger or build more muscle from extra protein shakes, even if they drink them after working out or before bed—just lifting weights is enough.

If you're a young guy who lifts weights and already eats enough protein, taking extra leucine pills for 12 weeks won't make you stronger or build more muscle in your thighs than just lifting weights by itself.