Whey Protein Isolates are 90% pure protein by weight. They are the purest and most expensive form of whey protein that exists. That's why they are the first ingredients you read on the 100% Whey Gold Standard label. By using Whey Protein Isolates as the primary protein source, Optimum Nutrition have been able to pack 24 grams of the purest, muscle-building protein per serving, with a lot less of the fat, cholesterol, lactose, and other stuff that you can do without. There's no question this is the standard by which other whey proteins are measured. Optimum Nutrition Whey has been the world’s Number 1 selling sports protein powder for over 20 years.