I found improvements after sticking with pectin and inulin for a week or so. Many people (including me) have a tendency to stop prebiotic foods because of digestive issues, but it takes time for the gut flora to adjust. Start with small amounts to see how well you tolerate them. You’ll want to avoid the higher-sugar foods until later on too. There’s probably a more extensive list, but Google isn’t being very helpful.
Pectin: citrus peel, cucumber, celery, tomatoes, apples.
Inlulin: leeks, onion, garlic, asparagus, artichokes, chicory.
Maybe you’d like the coconut bread in the recipe section. If you’re diabetic you’ll have even more reason than most people to avoid starchy, inflammatory foods like grains.