Amino acids in food make up protein. When protein is digested it is once again broken down into specific amino acids, that are then selectively put together for different uses. These new proteins formed in the body are what make up most solid matter in the body: skin, eyes, heart, intestines, bones and, of course, muscle.
That's why understanding what each of these aminos can do and getting more of them in your diet can be very beneficial to reaching specific goals, such as muscle building. Of course, one mustn't exaggerate, because a good protein balance is what provides health and stability, without it any of the amino acids can become toxic. An issue that has been brought up in the case of phenylalanine, but holds true for all amino acids. To counter potential harmful effects, getting enough vitamins and minerals is important because they insure proper conversion of protein to amino and vice versa. Depending on who you talk to, there are around 20 to 22 standard amino acids. Of those 20-22, 8 to 10 of them are considered essential, which means that you need to get a certain amount of them in your diet to function properly - our bodies cannot synthesize them from other materials, so we only get them from food. Since aminos are the building blocks of protein, I'm sure you get plenty of all of them, but this article will show you the benefits of supplementing with extra free form amino acids, going in to deep detail of what too much or too little of several of them can do, what they do in the body and how much and when you should use them.
Next to the 8 essential amino acids, there are around 14 non-essential amino acids and a whole host of other metabolites classed as amino acids which are derived from the 8 essential ones.