What Is Casein Protein?

Casein is a slow-digesting milk protein, making up around 80% of the protein found in cow's milk. Unlike whey, which is absorbed quickly, casein forms a gel-like substance in the stomach that releases amino acids steadily over several hours — which is why it's often called "night-time protein." That slow release makes it a solid choice before bed or during any long stretch without food, helping support muscle repair and reduce breakdown while you're not eating.

How Casein Protein Works

Because casein digests so slowly, it keeps a steady trickle of amino acids moving into your system for hours after you drink it — some research points to a release window of up to 7 hours. This is particularly useful overnight, when your body goes the longest without any nutrition. Studies looking at casein consumed before sleep have found it can support muscle protein synthesis through the night in people who train with resistance exercise.

Benefits of Casein Protein

• Overnight recovery — keeps amino acids available while you sleep, supporting repair and growth
• Satiety support — the slow digestion helps you feel fuller for longer, useful for hunger control
• Anti-catabolic effects — helps reduce muscle breakdown during fasting or extended gaps between meals

Popular Casein Proteins at Nutrition Warehouse NZ