Beef, dairy, wheat, and chicken are the most common culprits of food allergies in dogs. The development of food allergies, however, takes time. So the dog may have been eating the offending ingredients for quite a long time before symptoms develop. How is a Food Allergy Diagnosed in Dogs? A food trial using a hypoallergenic dog food is the only reliable way to diagnose food allergies in dogs. There are two ways to do this using a novel protein source or hydrolyzed protein.