Also people with dogs that have intolerances or food allergies should keep in mind that according to UC Davis Vet School, the most common causes of food problems are BEEF and CHICKEN and DAIRY PRODUCTS. Many of these diets people use to try to address allergies or tummy problems tend to contain, yes, raw beef, or chicken, or people get advice to add yoghurt 'to help their stomach'. All those things may actually be the *cause* of the problem in the first place. Elimination diets take weeks to test so it isn't adviseable to switch back and forth before giving a diet many, many weeks; and also make sure the dog gets NO TREATS that could have any allergans or upsetting ingredients.
I think a lot of ongoing problems are due to treats because people feed in treats the stuff that may not be in a special food.