Remember the post on how many calories etc 1gm of protein = 4 cals so yes if you take it without training you could end up putting on weight. They tend to have a few carbs in there too.

Some are high protein i.e.90%, some are less with more carbs

Protein is the building blocks of muscle into which there are 22 amino acids, which make up protein.

Remember teh rule about 1-1.5gm of protein per lb of body weight, well it can be hard to eat that much protein. This is why we supplement with protein powder. I need about 300gms of protein a day. Thats a lot of tuna and chicken.

It also help the body maintain an anabolic state(growing).

If you feel you are aching too much it could be because you have not recovered enough. Making sure you take enough protein is paramount to help the recovery process.

Paul.