So, I went horrifically off plan for the past 2 weeks (lots and lots of fast food), my daily calories stayed 1700-2200/day (yes, about 1000 over my goal).
i *gained* from 209lbs to 221lbs. i took the last 3 days - drinking about 3-4 liters of water per day, my calories were on the dot 1100-1200 each day.
so i KNOW i didnt eat enough to actually gain that much weight, if each lbs if 3500 calories and basally i burn about 2800-3100/day.
how did my weight go up so far??
sodium?? will it just drop back?
Probably sodium and the weight of the food, plus your body dealing with that much fast food that it hasn't had on a regular basis in a long time. Much of it should drop off.
Fast food has a LOT of salt, which makes you retain and your number is much higher than it actually is. Don't weigh yourself for a couple days (I know, it's hard) and keep doing what your doing: drink as much fresh water as possible. That will help flush all the stuff out of your system.
Honestly, don't try to freak out trying to figure out how many calories you ate vs burned while you were off track and how much of the extra weight is real weight or water weight. It won't change what happened or much you gained. Use that energy instead to working out and figuring out where you went wrong so it wont happen again!
ALSO- if you weighed yourself at night, you also have extra food in your tummy thats adding poundage. Wait a day or two and then weigh yourself first thing in the morning before you eat or drink.
I'd say 4 pounds of that gain is actually fat--the rest, who knows? Could be water retention throughout your organs. Hard to say. All you can do is get back on track and see what happens next! Chances are you'll drop again, but maybe not all of it, right away. It may take a couple of weeks to get back down.
I'm no expert, but am I understanding right that your normal intake is 700-1200 calories a day? If so, maybe your calories were way too low, your body went into starvation mode, and then when you ate more, it recovered by holding on to those calories? Years ago I lost a lot of weight eating between 800-1100 cals a day and working out. Lost about 100 pounds over 8 or 9 months. I put almost all of it back on in 4 once I quit doing that. What I took away from it was I couldn't starve myself and maintain a normal metabolism. Anyway, maybe I'm understanding wrong and of course everyone's right, that sodium could be doing in you in. Whatever it is, I hope it all comes off quick for you, I know you must have worked hard to lose it.
I doubt you gained 12 pounds of fat, but as to how much is fat and how much is water, I don't think there's anyway (maybe in a lab, but not reasonably at home) to tell.
You just do the best you can, and don't look back, and it is what it is.
Drinking extra water, reducing sodium intake, and increasing my normal protein to carb ratio, seem to help me get rid of water weight quickly. But water weight sometimes can take a while to lose. I've had bouts of water retention that have lasted for weeks. The only reason I knew it was water retention, is that for me, my rings get tight when it's water retention (even at my highest weight, my rings were comfortable when I wasn't retaining water, and tight when I was).
What everyone else said. Junk food has a LOT of sodium.
I posted this elsewhere. My housemate was out of town last week and I finally (finally) dropped below 160 - 159.4 to be exact.
Then he got home on Saturday and we went out to eat. Then we snacked in front of the TV on Sunday while watchign ball games. I KNOW I didn't eat 7 lbs worth of calories, but on Monday morning I was back up to 166.7
Now, Wedesday, I'm back down to 163, and I can well believe that I put on 3.5 lbs of fat, plus 4 more lbs of water retention.
It sucks, but I made the choice to not pay attention to what I was eating and now I have to deal with it. And so I'm moving forward and recommitting to being healthy and on plan this week.
Can someone explain?
What I took away from it was I couldn't starve myself and maintain a normal metabolism. Anyway, maybe I'm understanding wrong and of course everyone's right, that sodium could be doing in you in. Whatever it is, I hope it all comes off quick for you, I know you must have worked hard to lose it. 
