The study showed that whey and casein retained their fast- and slow-digestion profiles when consumed together. The slower digestion of casein resulted in more sustained elevations in circulating amino acids. Whereas early on, both whey and casein promoted similar increases in muscle protein synthesis. At four hours after ingestion, the amino acids from casein were being retained in muscle at double the rate as those from whey.
If you’re not consuming whey protein every 3 to 4 hours, consider using a meal replacement that provides a casein-whey combination for its sustained-release effect. Or add a scoop of casein protein to your whey shake. You can also mix your whey shake with a glass of milk to get the benefits of about 6 grams of casein protein from the milk.