Milk provides significant amounts of calcium, selenium, phosphorus, potassium, riboflavin and vitamin B-12, as well as vitamins A and D if the milk is fortified. The difference in calories between skim, reduced-fat and whole milk is mainly due to their fat content, but the amount of protein and carbohydrates also differs slightly among these types of milk.
Skim milk is the healthiest option, with 83 calories, 12.2 grams of carbohydrates, 0.2 gram of fat and 8.3 grams of protein per cup. Choose reduced-fat milk, and each cup has 122 calories, 11.7 grams of carbohydrates, 4.8 grams of fat and 8.1 grams of protein. Although whole milk has the same amount of carbohydrates as reduced-fat milk, it is higher in fat, with 7.9 grams, and lower in protein, with 7.7 grams. It is also higher in calories, with 149 per cup.
The carbohydrate content of a cup of milk is similar to that in a slice of bread or a small piece of fruit, according to the American Diabetes Association. The protein content is about the same as 2 tablespoons of peanut butter, an ounce of lean beef tenderloin or a cup of cooked quinoa.