If healthy young adults drink a casein protein shake before bed, they might burn slightly less fat overnight than if they had whey protein—but about the same amount as if they had nothing at all.

If you're a young adult who's overweight or obese, having a casein protein shake before bed doesn't seem to change your metabolism or fat burning in any clear way — it doesn't help or hurt much, based on the studies so far.

If young, healthy guys drink a protein shake with 30 grams of casein before bed after working out, their muscles may recover better overnight because their bodies are building more protein while they sleep.

If healthy guys drink a protein shake with 20-40 grams of casein right before bed, their bodies keep building muscle overnight — even if they worked out earlier in the day.

If young guys drink a protein shake with 30 grams of casein before bed after working out, their bodies keep building muscle overnight better than if they don’t.

When older guys drink a protein shake with 40 grams of casein right before bed, about half of that protein shows up in their blood overnight — meaning their bodies are good at digesting and using it while they sleep.