BCAA's and EAA's are specific types of amino acids. EAA's are essential amino acids, referring to the group of eight amino acids that cannot be synthesized by the body, and must be obtained through diet. The eight EAA's include isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Three of these - leucine, isoleucine, and valine - also belong to the BCAA category, which refers to branched chain amino acids.
EAA's are particularly interesting as supplements for those who fail to get enough amino acids through regular diet. BCAA supplements are good for those who focus on serious weight training. The three BCAA's comprise around a third of skeletal muscles, and have been shown to be essential for forming muscles, and effective at slowing muscle degradation. BCAA's are metabolized by muscle tissue, which makes the amino acids readily available for building muscle or as building blocks for the muscles.