Protein gets a lot of buzz. It's the miracle food that builds muscle, right? Well, sort of. Proteins are a series of amino acids necessary for the body to build muscle and lean tissue. Proteins are incomplete, meaning some but not all of the necessary amino acids, in vegetables and whole grains. Proteins are complete in animal products and soy products. That is why soy is so valuable in a vegan or reduced animal diet plan. There are other ways to create whole proteins by combining incomplete ones, listed here http://www.bodyforlife2.com/incompletprotein.htm .
There are other ways of getting protein, like in a whey powder form. Just remember that more processed foods have less nutrients and more additives. OR, they could have dangerous additives, such as EAS Muscle Milk, which has had problems recently with large amounts of cadmium (a lethal metal substance) found in the drinks and powders.
Protein is great because it keeps the body satiated longer than most carbohydrates. The down side is that a lot of them have large amounts of fat, too. Some are healthy fats, which I will get to next time, but fats are very dense and can add calories quickly.
The healthiest animal sources of protein are poultry breast and low mercury fish (wild salmon, light tuna). The healthiest soy option would be tofu. Do not limit your diet to all protein, or even mostly protein because the body does not like to use protein for energy. So, if your diet is out of balance with protein taking too much of a lead, you may feel less energy to get the workout done. The other downside is that the kidneys and liver do not like too much protein. Extreme protein dieting can lead to ketosis, which is a serious kidney condition.
Of course, the other thing to remember is that any calorie the body doesn't need becomes fat. So, if you are ingesting a ton of protein and the body does not have any reason to build that much muscle or need those amino acids at that time, then fat stores will increase. Muscle is built from exercise, and no amount of ingested protein can change what your body wants to build.