A true fast is not eating, and just changing your eating habits to the night time.
Corrected from above:
They eat in the moonlight. Sleeping during the sunlight.
At times they stuff themselves during the moonlight and fast during the sunlight. The more devout only eat, not party.
A true fast, as practiced by most observant Jews and Christians is not eating, and only drinking water, not just changing your eating habits so you only eat at night time.
That being said a loss of weight tends to bring about an end to Type 2 diabetes in many people.