Hey BumSetSpike,
First of all, 500-700 cals a day is FAR too low!

I don't use Alli, so I don't know what that supplement's literature says, but normally 1200 cals a day average is considered the lower limit for healthy weight loss. If you go lower, you are not getting sufficient nutrients for basic needs.
Second of all, I don't know what you mean by a "free day." If you mean, eat whatever you want (and skip the Alli) and not record what you eat, I just never do that. I may have days where I choose to eat more than usual, but I always record everything. Everything! Because believe me, your body is recording everything, whether your mind is calling it a free day or not.
Good luck!
Jay