Consuming 20–40 grams of protein, particularly casein, approximately 30 minutes before sleep stimulates overnight muscle protein synthesis in both young and elderly men and enhances muscle mass and strength gains over 10–12 weeks of resistance training in young men.

Study: Protein Ingestion before Sleep Increases Overnight Muscle Protein Synthesis Rates in Healthy Older Men: A Randomized Controlled Trial.

The study shows that older men who drink a protein shake before bed build more muscle overnight, especially with 40 grams. But it doesn’t prove that young men get stronger or bigger muscles over weeks, which the claim also says.

Study: Protein Ingestion before Sleep Increases Muscle Mass and Strength Gains during Prolonged Resistance-Type Exercise Training in Healthy Young Men.

The study gave young men a protein shake before bed during 12 weeks of weight training and found they gained more muscle and strength than those who didn’t. This matches the claim that pre-sleep protein helps build muscle.

Study: Effects of pre-sleep protein consumption on muscle-related outcomes - A systematic review.

The study shows that drinking a protein shake before bed helps build muscle overnight and improves strength gains during weeks of training in young men, just like the claim says.

Study: Effects of pre-sleep protein consumption on muscle-related outcomes - A systematic review.

The study shows that drinking a protein shake before bed helps build muscle overnight and improves gains from weight training in young men, just like the claim says.