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When you digest protein it's broken down to amino acids, these are what's used to build muscle. There are different amino acids needed and the body can break down certain ones to build others as it needs. Certain amino acids can't be made though, you really have to get protein that has them. These are called essential amino acids.
Not all protein are the same, most plant protein are non complete proteins coz they lack certain essential amino acids. Whey protein is popular because it is considered a complete protein and contains all 9 essential amino acids.
With whey a lot of people check out the protein per scoop as their basis for selecting a brand. What some companies do is add certain amino acids that are cheaper than whey. Simply put, these however aren't as useful to the body as simply adding more whey. You end up taking more of a specific amino acid whereas your body needs a balance of the different types. As a result the company can boast a higher protein per scoop even if it's lower with respect to what your body uses.
Whey that have creatine included in it end up fooling certain tests used to measure the amount of protein. So I avoid those too.
To add, the body releases cortisol about 45mins. after exercise. What this does is breakdown muscle to turn it into energy. The body developed this because in caveman days, if you're still doing something strenuous after 45mins. it's likely something life threatening. So losing muscle was not so bad compared to being dead. Nowadays you can't just tell your body not to do it. So best advice is keep workouts short.
Studies have shown however that consuming quickly absorbed carbs and protein prevents the body from releasing cortisol. Since there is now a source of energy from the carbs, the body doesn't need to break down muscle.