 In animals , amino acids are obtained through the consumption of foods containing protein . <unk> proteins are then broken down into amino acids through <unk> , which typically involves <unk> of the protein through exposure to acid and hydrolysis by enzymes called <unk> . Some ingested amino acids are used for protein <unk> , while others are converted to glucose through <unk> , or fed into the <unk> acid cycle . This use of protein as a fuel is particularly important under starvation conditions as it allows the body 's own proteins to be used to support life , particularly those found in muscle . <unk> acids are also an important dietary source of nitrogen . 
