The amount of fiber that your dog should consume is an issue which depends on your dog’s size, breed, and your vet’s recommendations. Fiber comes in soluble and insoluble varieties. A diabetic dog is dealing with high levels of blood sugar which you should avoid raising if you can help it. Soluble fiber slows digestion and food transiting into their stomach, while insoluble fiber helps them to feel full and reduces their appetite. So, if your dog is overweight, food of greater than 15% of the dry matter of fiber is probably wanted, whereas more average sized dogs may need food of anywhere between 5-15% of the dry matter. Again, remember that there are only rough guidelines.