Just too let you know, I've just recently gone through a great amount of research on this same subject, so by all means use what I've learned for yourself. Remember that what works for one dog don't always work for another. It is always trial and error to find out for yourself what works best.
Dog food/supplements with any of the following ingredients: Grains/glutens (wheat, barley, rye, oats, rice, corn, breads, crackers, cookies, flours, yeast, etc.), any soy (soybeans and processed foods containing soy), casein (all milk and dairy products, all cheeses, ice cream, butter, cream cheese, cottage cheese, etc.) chemicals (MSG, BHT, BHA, ethoxiquin, estrogen/hormones, colors, artificial flavors/ preservatives), aspartame (sweeteners), sugar, salt, hydrogenated oils, sometimes kelp with some dogs, all nuts (almonds, peanuts, peanut butter, cashews, pistachios, except tree nuts like walnuts), seeds (sunflower, pumpkin, and sometimes flaxseed with some dogs), some vegetables and fruits (beets, beet pulp, peppers, beans except green beans, apples, dates, raisins, plums, grapes, figs, cherries) and all pre-made processed foods that include (chicken, turkey, pork, rabbit, lamb, fish, soups, boxed/canned foods,) etc. can be very hard on a dog with food allergies. There are primary and secondary problems with foods. For instance, wheat is extremely high on the list and is primary, while oats is on the lower spectrum and could be considered secondary. Most meat is considered secondary and are man-made/processed foods which are loaded these days with chemicals like MSG and hormones that can set allergies off. If you process your own meat or use a different type like deer or bison, then it is less likely for problems to arise.
For the most part, grains/gluten and milk products are the highest ingredients known for causing leaky gut syndrome, IBS, etc. Grains are well known to be used in factories to make glue. Everybody knows you put water and flour together and it makes a glue-paste, well it does this also in your body, which is very hard to digest. The dog cannot get adequate nutrition that it needs because everything is absorbed by the glue in its body. Many longtime breeders have been preaching this for years.
Dogs, cats, and even people suffer from these same foods which causes them many ailments. If a dog has been eating the same food for years, they can still develop food allergies from these types of foods at any one time. You can read a great deal more about this if you do a general search on google.
A known dog food is used by vets for such sensitive stomachs and food allergies. It is the IVD Duck and Potato that you can get from their practice. You can also try DVP Natural Balance Duck and Potato that is sold in most pet stores and is very similar to the same product your vet sells. The reason for Duck/Potato is simple. Other meat sources including fish and lamb, other carbohydrates sources including rice and oats, have been used in kibble and can still cause allergies. These two ingredients haven't.
Here is the site for
DVP
Keep your dog totally on this food. You can give these helpful and safe vitamins: E, Ester-C, and B-6 or B-complex. No dog treats unless it is the Duck and Potato treats. No people food! Do this process of elimination for at least three months for a total detoxification.
Then if your dog has improved, offer only one safe food product for a week. Most safe food products include certain vegetables and fruit. If symptoms develop again, stop that one ingredient, make a note that your dog is allergic to it and never feed them that again. It is very hard to remember not to ever give in to those begging eyes for a bite of French fries or pizza... but if you want your dog healthy, you have to just say no!
Best of luck too you!!!