Milk [the liquid drink] is allowed in later stages of Atkins, though not on induction. That said, Milk is basically composed of Skim Milk [Curds and Whey] and Cream. The Curds are used [along with some of the Cream] to make Cheese. The Cream is used to make Butter as well as Whipping Cream and Heavy Cream. The Whey can be used to make Ricotta Cheese or to extract Whey Protein. Pretty much the only thing left over after they've extracted all these Low-Carb foods from the Milk is the Water and Sugar [Lactose.]

In addition, Carb Countdown has a Low-Carb Milk, which is made from Skim Milk, Water, Cream (?,) and some other ingredients. I believe Milk Proteins, etc...but am not 100% sure.