Nonfat or skim milk must by law contain less than ½ percent milk fat. Both lowfat and nonfat milk are available with milk solids added, in which case the label states "Protein-fortified." This not only boosts the protein to 10 grams per cup but also adds body and richness. Federal law requires that both lowfat and nonfat milk be fortified with 2,000 International Units (IU) of vitamin A per quart. Though vitamin D fortification is optional, 400 IU per quart is usually also added.