Lactose Intolerance: Symptoms, Diagnosis & Treatments How do I know if processed foods contain lactose? When buying food, read the ingredients on food labels carefully. Ingredients derived from milk that contain lactose include: Whey. Cheese. Milk by-products. Dry milk solids. Lactose. Butter. Curds. Nonfat dry milk. Dry milk powder. Also avoid items that state "may contain milk" on the food label.