A pet food containing naturally occurring copper that can be used as a prophylactic diet to prevent and/or reduce copper storage disease, dilated cardiomyopathy, adverse gastrointestinal food reactions, and/or food allergies in pets is provided. A method for forming this pet food containing naturally occurring copper includes: providing a formula selected from the group consisting of chicken meal, corn gluten, duck, rabbit, venison, fish, peas, potato, barley, rice, corn, and any combinations thereof; and adding one or more ingredients having a naturally occurring copper source to provide a naturally occurring copper concentration in the pet food composition from about 7.3 ppm to about 25.0 ppm, adjusted for a dry matter basis.