Dairy source of protein (other than cassein), known for high levels of BCAA's and high nitrogen retention. Made from milk curd, whey protein is the Rolls Royce of proteins because it has a superior amino acid composition (including high levels of leucine, arguably the most important branched chain amino acid), superior biological value (meaning that more of what you eat gets digested and into your system), is very low in lactose (a milk sugar that most adults have difficulty digesting).