Since milk is one of the most commonly used dairy products, one frequently asked question is how types of milk differ. Whole milk, also referred to as vitamin D milk, contains 3.25% fat by weight and is the closest version of milk to what comes directly from the cow. All milk sold in major retailers goes through a pasteurization process, but the amount of milkfat that remains in the milk differentiates the four main types. As the name suggests, 2% contains 2% fat by weight, while skim milk contains no fat. The amount of milkfat impacts the fat grams and number of calories in each serving of milk.