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When people think of protein powder they automatically think of whey - lots of leucine, lots of BCAAs, fast absorbing - just an all around great tool for building a bigger stronger body. But in our whey-centric world we often forget about the other milk protein - casein. Casein makes up 80% of the protein found in milk, with whey making up the difference.
One of the major differences between whey and casein is how they are absorbed and utilized by the body. After ingestion both proteins cause an increase in blood amino acids levels. Comparatively, the spike from whey occurs faster and is higher. As a result, blood amino acid levels driven by whey ingestion decrease rapidly. Casein causes a slower rise in blood amino acids levels, which is then sustained for a longer period of time. Looking at the kinetics of their actions and impact on the body, you can think of whey as potentially being more anabolic while casein acts in a more anti-catabolic fashion.
Casein & Protein Synthesis
Sometimes slower is better. A 2012 study published in the American Journal of Physiology, Endocrinology, and Metabolism found that after 4 hours the amino acids from casein were better assimilated and retained by participants muscles compared to whey. The slower digestion profile of casein also makes it an ideal candidate for your late night protein of choice. The benefit of casein over whey before bed has been long speculated due to the absorption differences in the two proteins. Since casein is absorbed more slowly it would make sense to have it before bed when you aren't going to be eating for a while.
A 2012 study published in Medicine and Science in Sports and Exercise found that 40 grams of casein taken before bed increased muscle protein synthesis rates by 22% over the course of the study participants' 7 1/2 hour slumber. Unfortunately they did not pit casein against whey so we don't have that comparison to make but we do now have evidence to show that the slower absorption profile of casein plays to its benefit at night.
Casein & Fat Loss
From a fat loss perspective, casein may also provide a satiety advantage. A 2011 study published in Nutrition Journal report that study participants experienced greater satiety when given a protein shake containing 20g of casein vs. whey before eating a meal. We all know that protein has a satiating effect due to its impact on digestive hormones. The slower releasing profile of casein may enhance that effect.
Casein & Practical Use
From a practical standpoint casein just makes shakes taste better. Whey is watery but the addition of casein or having a casein by itself is a game changer when it comes to texture and mouthfeel. If you always use whey in your shakes then you are in for an incredible surprise when you start using casein instead. The one downside to casein is that some people may be allergic to casein over whey, though this is still a small portion of the population. If you're like most people, however, you are in the clear and can reap the benefits of this great protein.