The weight difference is water. But if you loose a third of the calories when converting to cheese then I assume they're in the whey. I doubt that people who were hard up for calories would discard the whey unless they had some cultural objection or superstition.
That may be part of it, but another large part of the difference is that, as previously stated, turning milk into cheese destroys lactose. You get fewer calories from the cheese because microbes already used up some of the calories that were originally in the milk in order to turn it into cheese, and thus those calories are no longer available for you.
> I doubt that people who were hard up for calories would discard the whey unless they had some cultural objection or superstition.
Indeed, Norwegian goat cheese is a whey cheese, made by boiling milk, cream and whey leftover from other production (such as more usual casein based cheese). There are a number of other traditional whey cheeses from other countries as well.
