I think beer does it to me...
On my day often sometimes I will have a couple beers. And I don't watch the calories of course, though I don't go crazy. Come Monday morning the scale has jumped, my wife has fainted and I am left explaining its normal. In fact, those few extra pounds not only come off, but I have consistently been losing an extra 2 pounds a week for some time. Could be the food for me too, but I am not sure. I don't go too crazy, I think the beer is the worst of it.
Hmm.. Come to think of it, this week was a great example. I had 3 big cans of beer and we ate spicy sichaun in a great little restaurant. Plus I had an ice cream later. No idea the calories, not interested.

Monday morning I weighed in at 261 from 257 on Friday. My wife LOST it!!! She panicked and I just laughed and told her to trust me. Today I hoped on the scale and it is 256. Did 1 lose 5 pounds of fat in 2 days? No, I lost 1 pound, the rest must have been water or something. I have told my wife I will very easily be in the 255 range by Friday or Saturday, but she really doesn't believe me. She will see.
Have fun sometimes, if it really bugs you, just exercise a little more. Thats what I did until I was confident it was just a temporary water gain.
sirant