Whey concentrate is the least processed kind of whey protein powder, so it has the most carbohydrates and fat. (About three grams each per 20-25 grams of protein.) Whey isolate is further processed in a way that reduces most of the carbs and fat. Some whey isolates contain no carbs or fat whatsoever. This makes it more diets that severely restrict carbohydrates and/or fat, though the taste does suffer somewhat.