Protein fuels the muscles, boosts metabolism and keeps hunger at bay. Some research has even shown losing weight highly depends on your protein intake, from lean meats to vegetables.  Proteins are made up of amino acids, which are the building blocks of the body. Your body uses amino acids to make new tissues and repair damaged tissue, among other functions. There are hundreds of amino acids, such as glutamic acid, leucine, tyrosine, glycine, histidine, arginine, and cysteine.  Amino acids necessary for the proper function of the body can be found in high-protein foods like beans, lentils, broccoli, spinach, eggs, meat and fish.