Lactose is the sugar is naturally found in the milk of all mammals, but is not found anywhere else in nature. Our body cannot absorb lactose because the molecule is too large to pass through the small intestinal wall and enter our blood stream. The lactose molecule must first be split into two smaller molecules (glucose and galactose) that we can absorb. This is done by an enzyme located in the intestinal wall called lactase. As we age, some of us lose significant amounts of this enzyme, and we can no longer digest milk sugar. Whey is a dairy protein that is a by-product of the cheese making process. In its raw state, whey contains substantial amounts of fat and lactose (milk sugar). You wouldn't want to eat raw whey. That's why it is filtered and processed: to remove most of the lactose and fat. If you've ever heard of "microfiltration" or "ion exchange," those are simply methods of separating the fat and lactose from the protein. The end result is a more concentrated protein.