A month ago, I made some changes to my diet after my doc ominously dropped the D word. Basically, I've started doing an Atkins-like program... still trying to keep carbs to 20g or less per day, but I haven't been following it as strictly as I could have. End results is that I've lost around 18.2 pounds in a month's time.
Naturally, I saw the biggest loss while working outside in the heat. I was drinking around 4-6 liters of water a day but still losing 4-6 lbs. Those losses were temporary, however, and after the brush clearing had ended the weight went back up to where it was when I started the work.
I'm also finding that while a minor deviation from the carb limit has a small effect of either arresting weight loss or even adding a pound or two, a major lapse can have a huge, huge impact. For example, a PBJ sandwich probably means no progress the next day, but a pizza could cost up to 7 lbs (depending on how much I pig out). The good news is that, like losses from working out, the weight gain appears to be mostly temporary. My supposition is that the increase in complex carbs (and sodium) causes the body to retain more water the next day.
So. General conclusions:
* heavy physical activity (although you need to do it for overall health) is only a temporary weight loss... stop working out or reduce the activity and the weight comes back
* the amount of complex carbs seems to play a bigger role than calories
* sodium can jack up the equation (ie, a Coke Zero has no calories or carbs, but it does have sodium that can prevent you from losing water weight) unless you're sweating it out
* occasional small cheating a couple of times during the week is better than one big mega-cheat once every two weeks