Why does a cup of fat free milk have 12 grams of sugar?

A cup of fat-free milk contains about 12 grams of sugar primarily due to lactose, the natural sugar found in milk. Lactose is a disaccharide made up of glucose and galactose and contributes to the overall carbohydrate content of dairy products. Although fat-free milk has little to no fat, the lactose content remains unchanged, which is why it still has a notable amount of sugar.