Re: Why are the lactose levels are different in whole and skim milk?

Well, I'm not sure that I agree with you that skim milk will contain less lactose than whole milk. Homogenized whole milk is a fat-in-water emulsion, like oil and vinegar salad dressing. Lactose is soluble in the 'water phase' of this emulsion, but not in the fat phase. If you process the milk to take away the fat, the lactose remains behind in the skim milk and is now effectively MORE concentrated [1].

[1]Fennema, O. 1996 Food Chemistry, 3rd ed. Marcel Dekker, New York.

*Please note: The author is answering on his own behalf, and his answer does not represent a statement from the USDA.