According to the First Law of Thermodynamics (e.g. matter can't be created or destroyed), there's no way a 7-lb gain from a single meal can be fat -- it HAS to be water. You ate, what, a pound of bad food? Even if every bit of the food was converted to stored fat, that's still only a 1lb gain, leaving 6 lbs of water. You can't create more fat than the weight of the food you started with -- it's got to be created from something, right?

Some people just put on more water weight than others, or hang on to it longer. But unlike fat, it does fall off after a while, so it's not like you'll be permanently undoing your hard work if you do cheat. It all depends on how well you cope with a week's worth of bloat. Me, I'd probably take my chances with the bloat for a real gourmet dining experience, the kind where you'll remember the exact menu years from now. I'm not a big advocate of cheating, but there are some legitimate big-deal food experiences that I think are justifiable, and I think a restaurant that's worth flying cross-country to visit qualifies!