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Breaking it down…fractions of Whey Protein

Whey protein is a dairy protein, derived from milk as part of the cheese making process. Milk is approximately 80% casein and 20% whey protein. Casein is a slow-release protein, so for fast recovery after exercise whey protein is preferred. As a comparison we use whey protein concentrate and whey protein isolate in SiS Whey Protein for fast release protein, and we use milk protein isolate in our Overnight Protein shake to provide a source of slowly released protein as you sleep.

Whey protein has a complete amino acid profile, meaning that it contains all twenty amino acids, including the essential amino acids that your body must ingest and cannot make itself. Amino acids are the building blocks for all of your bodies’ structures such as muscle, bone and tendon, and other key elements such as enzymes and hormones.


Whey protein is naturally high in the branched chain amino acids leucine, isoleucine and valine. BCAAs make up approximately 35% of your lean muscle mass, so play a key role in the growth and maintenance of muscle protein. It is also the most readily broken down for energy when there is low carbohydrate availability either during fasted training or during high volumes of endurance training.

Whey protein concentrate is naturally sweeter as more of the lactose (milk sugar) is left behind. Whey protein isolate is lower in carbohydrate and fat, but it is more bitter. By the time you get down to individual amino acids the taste is very bitter. As the fractions of protein get smaller, the cost also increases significantly.

Maintaining a positive protein balance is very important to ensuring full recovery from training and supporting adaptations. After training the body can end up in a catabolic state, meaning that it will be breaking down more protein that it is making. An effect of exercise is that the pathways which make new muscle protein become inhibited. By feeding protein around training you can prevent this from happening by creating a positive protein balance and increasing the levels of leucine available to cells to overcome this post-exercise inhibition.

The inhibition of muscle protein synthesis can be overcome when significant amounts of leucine are fed, i.e. at least 2-3g. Leucine switches on the mTOR response within existing muscle cells to produce more new muscle protein. mTOR is the messenger RNA (mRNA) for new muscle protein. RNA looks like half of a DNA structure, and dietary protein is needed as a source of bases to match the bases of the mRNA to make a new protein.

In summary, the ideal protein product should contain around 20-25g of protein, with at least 2g of leucine included. What fraction of protein you choose to get this from is up to you, based on taste, price and preference. Also consider whether you need to replenish carbohydrate or not if you have done a long endurance or high intensity session.

Written By

The Performance Solutions Team