I just read you post regardging your Belveder's diabetes issues.  I am sorry that you are having to go through this, it is very difficult.  We have had one diabetic Corgi.  We discovered Junior was diabetic after he began to drink excess amount of water and having accidents in the house.  After he had been on insulin for about 6 or 8 months we also went through issues related to his blood sugar floating up and down.  I am sure that your vet talked to you regarding keeping syrup to rub on his gums in case of a  low sugar episode and we did have to use that trick a couple of times while attempting to regulate his dosage. 

To answer your question, we did go through a time when it seemed that Junior had adjusted to the insulin and it seemed to increase effeciency and we actually lowered his dosage by 1 unit in the AM and PM.  When his drinking increased and he had accidents we ticked it back up by 1/2 unit and it seemed to stabalize him. 

I am not certain why he seemed to "adjust" to the insulin.  I sometimes wonder if the unregulated dog food industry had something to do with it since there are not alot of checks and balances regarding the protien content or formula changes related to dog foods. 

We have not ever been in a situation from a time standpoint that we could feed an all natural diet. 

Remember to talk to your vet regarding changes in Belvedere's situation and allow them to make recomendations.......but understand that no one including your vet can understand your dogs condition more than you......you see him WAY more that your vet.  We reached a point that we had to find a balance which included a lower dose in the AM than the PM due to activitiy level etc.

So many factors can effect diabetes just like they do in people.  Activity level, diet, and other factors do effect the insulin.  Hang in there and know that there are sometimes periods when external factors can affect the insulin.