Can you gain more weight then you eat?

[troy j]

I have heard that if you take in 500 more calories then you burn each day you will gain a pound in weight, but lets say that you eat 1 pound of a high calorie item could you gain more then 1 pound in weight? and if so then where would that mass come from, because my brain says 1 pound in means I cannot gain more then 1 pound.