Which visa? I definitely didn't gain any weight waiting for my first (fiance) visa as I was working extra shifts to save money and my job was active and I walked to and from work every day. In fact, that's the thinnest I've been in the past few years. The next two visas got easier stress-wise (and preparation-wise) so there was less worrying. Don't think I overate as direct result of either of them, but I'm not as thin as I was during the first one!