👉 Methionine, also known as leucine or leucine-lysine, is a non-essential amino acid that is found in animal foods such as meat and dairy products. It is an essential amino acid because it is required for protein synthesis, which is the process by which cells make proteins to build tissues and organs. In humans, methionine is crucial for the production of white blood cells, which are involved in fighting off infections and diseases. However, some animals,