@adriana28 I'm going to upset some people here, but ah well...
3 lbs is ~10500 calories. Spread over 4 days that would be 2625 calories per day. Not total, not over your deficit, but over your maintenance.
So if your maintenance is 1800 and you were eating 4,425 calories per day for 4 days... yes, it's possible that it's all fat.
If your maintenance is 1500, then 4125 would do it.
Everyone saying it's impossible is wrong. It's definitely possible. I've done it myself.
A cheeseburger (800) with minimal toppings, fries (950) and a shake (650 base, + ~300 for any mix ins) is an easy 2700. A nice normal 300 calorie breakfast puts me at 3k. And that's without any dinner or snacks yet.
It's possible you gained 3 lbs of fat.
However...
I'm currently 233.8 lbs. I started at 274.4 lbs. I was averaging 4000 calories per day, and let me tell ya... even then I knew it was an insane amount of food. I highly doubt you went that far off plan.
What's more likely is that it's a combination of many things:
1) normal weight fluctuations
2) water retention from a change in the type of food you're eating
3) the actual weight of the undigested food still in your body, and
4) yes, some actual fat gain.
No, you don't have to eat at 1200 forever. But you do have to eat at or below whatever
your maintenance calories are, forever, if you don't want to gain weight.
If those maintenance calories are too low, you have to be more active to raise them.
If you want a higher calorie day, you have to have a couple of lower calorie days, or burn more calories.
If you want to go off book for 4 days, you'll probably need to diet for a couple of weeks to make up for it... or burn more calories.
It sucks, but that's the way it is.
And whatever it is, you know what plan you need to follow to get to your goal. Whether you gained water or fat or muscle or nothing at all... you still need to get back on your plan. It's okay to fall off, as long as you get back on track. ❤