If you are prescribing to main stream medical practice, that is true. According to many studies from other sources however, there are a few possibilities. If you are serious about diet, you need to look outside the standard sources.
There are many, but if you are interested in diet specifically, I recommend looking into The Gerson Diet. I've had family and friends report success from these methods. You can find their main site here: http://www.gerson.org/
The Gerson Diet is one of all natural and raw foods for healing as well as non drug related treatments. They claim to cure all manner of disease and illness. To avoid plagiary and keep the answer simple, I will state that on the first page, is a summary of known problems it claims to cure, including diabetes.
As always, I am not part of, nor do I endorse any organizations. I do however recommend researching everything for yourself. I do NOT recommend simply trusting that ANYONE has only your best interest at heart. There are unfortunately too many people who want your money more than your health.