Not sure the status of Nashville fit any more as, well, it seems dead as 2 doornails, but figured I would post the details and what it has done for me.
The theory (and you don't have to buy anything as a note) is that on an up day, you eat normally.. and I stress normally... don't stuff your face with 6000 calories because you're worried you might be hungry tomorrow.
The down day (every other day) you eat about a 20%-30% of your resting calories. You can find information on this here: http://www.johnsonupdaydowndaydiet.com/
From the simple caloric standpoint, you're dropping about 1/3rd of your calories, which for an average 2500 calorie diet means dropping 5775 calories a week (or 1.65 pounds @ 3500 calories a pound), 4620 cals a week on a 2000 cal diet (1.32 pounds)
The caloric reduction is evident, the mental aspects of it are interesting as well... on a general diet I was always annoyed that I couldn't have the food I wanted... on the Juddd I can have it the next day if I want it. I've found that on up days I don't really go hog wild or feel the need to stuff my face, and the calories are about where they should be for maintenance. On the down days, I plan some meals, low cal snacks, and try to not watch the food network.
Generally not hungry, but energy levels a little lower.
2 weeks now, did the average male "drop 5 pounds in the first week" thing, and am now at 8 pounds down from my weigh in 2 weeks ago (which means I lost nearly 3 pounds on a non-first-week-loss)
So anyway, if you're wanting to try it
eat normally day 1
Day 2 eat ~20% of your resting rate (basal metabolic rate, not your average calories per day, these weeks are hard)
you can increase your down day calories to a higher percentage
Exercise lightly on down days (if you do) -for the first couple of weeks while your body starts learning to burn fat for energy again.
Get protein for mental energy (egg whites = lots of protein, very low calories.. combine with zucchini and some tomato for an omelet that is filling and low calories. Alternately get a protein shake)
Weigh yourself once a week on the morning of an up day (you'll be at your lightest)
Don't expect the first week's results to continue past the 2nd week... the trick there is you're losing some of the food you're carrying in your belly. You carry roughly 6-10 pounds in there... after a week it's down to whatever you eat or dink on an up day.
And it goes without saying, but if you're miserable, stop...