It's based primarily on what the book of Daniel records that he, Azariah, Mahalel and Hananiah ate, with additional restrictions taken from the fast Daniel kept while praying for the return of the Jews to Jerusalem. I lost about 20 pounds on it over a two-week period this past June.
It's pretty straightforward. Under this regimen, you can eat any fruit, vegetable, nut, legume, root or whole grain that you want, cooked or raw. Use any natural herbs or seasonings that you want. You drink water. Quantities are unlimited, so there's no worries about getting enough calories.
The benefits of a vegetarian diet are pretty well documented, so it's not too surprising that the book of Daniel reports that he and his friends outperformed both physically and mentally those who ate choice meats and drank fine wines.
From a proscriptive angle, the Daniel fast allows no meat, no dairy, no eggs, no sweeteners of any sort (including honey) and no flour. This pretty much eliminates all processed foods, so you can see why it's a big saver on the waistline. In the first few days alone, a person usually drops about 10 pounds of retained water.
The downside is that this is a big change from the diet we're accustomed to eating as Americans, and we can get strong cravings those first few days for junk food, or just find ourselves hungry for more food.
At the same time, though, that is part of the appeal of the Daniel fast both for losing weight and for being able to stick to the commitment -- if you're hungry, just get something to eat. You're not relying on willpower alone to tough it out for the duration of the fast; you're training yourself to eat more healthily, and you're breaking an addiction to unhealthful habits the way you're supposed to -- by replacing them with good habits.
One thing I discovered after trying the Daniel fast in June was that, after a few weeks without meat and sugar, I really didn't have an appetite for them. They not only lost their taste to me, they annoyed my stomach. If I hadn't insisted on getting back into some unhealthy eating habits for the sake of convenience, I probably would have stuck with it just fine.
Make that a goal for 2013.