You would have had to eat an extra 7000 calories in one day to gain that amount of weight. That is practically impossible!
It's probably water weight, or you're holding on to some mass in your gut (it takes time for those unlimited veggies to make it through your system!), and, if you're a girl, your hormonal cycle will affect water retention. I fluctuate up to 5 pounds in a single day (although usually only about 2) and only weigh about 120 lbs.
If you're worried about these types of minor weight gains over extremely short periods of time, I agree with the previous poster: Put the scale away! I'm the opposite: seeing those fluctuations throughout the week reminds me not to freak out just because I had a 'bad' weekly weigh-in.
| current weight: 120.0