Some people's physiology might make that possible... I'm guessing that if such a gain were to happen, it would be mostly water weight accompanying ridiculously high levels of sodium intake from "see food" diet. I've seen people gain healthy weight pretty fast, but it's usually when they are severely underweight already. Generally people do struggle with losing it, but in reality, the body loses just as fast as it gains. People struggle because it involves much more will power to constrict their diet than it does to chow down daily. Steve... don't worry. You sound like you are interested in gaining weight, not losing it right? I'm guessing that any fat (or spares, as I take your comment to mean) you put on will be easily lost if you just keep active in cycling.