http://skeptvet.com/Blog/category/nutrition/
You may find some helpful information at the above site. I would proceed with caution.
PS: Changes in behavior and appetite suggest a visit to a veterinarian may be in order.
Has the dog had a senior workup? Basic lab work/blood tests could detect things that would explain the changes. Then you could discuss treatment options with your vet.
Think about it, how can anyone who is not a veterinarian and who has not examined your dog advise you accordingly?
