My dog has GI disease, no vet. What food helps with weight gain?

Poor guy. It is hard to say what and how you should treat him without running any kind of testing to determine exactly what GI disease he has. Some GI diseases include intestinal parasites, inflammatory bowel disease, lymphoma (cancer of the intestines). There are also some underlying disorders that maninfest through the GI tract which includes: pancreatitis, gallbladder disease, and malabsorption disorders (VIt B deficiency) just to name a few.

I am not sure what your pets exact symptoms are but you can try feeding him a bland diet of boiled plain chicken and rice or cottage cheese, added fiber (1-2 tsp of canned pumpkin, not the pie filling, in his food daily), and probiotics (Culturelle over the counter). I would also recommend treating him with a broad spectrum dewormer such as Pyrantel Palmoate or Fenbendazole (Panacur) from your local pet store or feed store.

Please feel free to repost your question with more specirics about your pets actual symptoms. I would also encourage you to go outside your local area to find a vet to see him if he does not respond well to the suggestions above. I hope that your pet gets well soon. Best wishes and take care.