Protein is an important part of your body. It helps repair and build tissue in bones, blood and skin, but here we are focussing on the muscles.
After working out, our body repairs damaged muscle fibres by fusing them together in cells, forming new muscle protein strands. These repaired strands or myofibrils increase in number and thickness to create muscle hypertrophy. Muscle growth can only occur if the rate of protein synthesis is greater than the rate of muscle protein breakdown. This is achieved by forcing our muscles to adapt, by generating stress that is more intense than the one our body was previously used to. Muscle growth occurs while resting after workout. For this process to work successfully we need enough protein to sustain the cells, and that is when our protein shakes may come in, after the workout.
Protein, unlike carbohydrates and fat, cannot be stored. Proteins are ultimately digested to form ammonia. This ammonia is broken down into urea in the urea cycle. Left over carbon skeletons are converted into glucose, which can be used by our bodies to generate energy (in the form of ATP) through respiration. If our cells have enough glucose, and there is no space left to store it as glycogen, the excess glucose is converted into fat and stored. Our fat storage is pretty much endless and thus excess protein intake will result in weight gain in the form of fat. It is very easy to overshoot the intake, as one serving of protein contributes to about one third of the recommended daily intake.
Protein supplements can be healthy, but they have to be taken with caution and always as a supplement, never as a dietary substitute. Some people cut down their carbohydrate intakes when they start to use protein, however this can lead to a state of ketosis (dehydration, vomiting and confusion). My recommendation is to adhere to a balanced diet of fish, lean meat, fruit, vegetables, whole grain and carbohydrates, and supplement it with protein shakes if necessary.
