My appetite sky rocketed, but so did my energy levels and my interest in working out, so I haven't really gained much weight and what I did was muscle. However, I do think that if I'd stuck with the same sedentary lifestyle I was living and started eating like I do now, I would have gained weight. IMO, it's mostly an increase of appetite combined with poor choice of foods and a lack of interest in working out. Some people are, obviously, just more genetically inclined to gaining weight, but I think that's where the idea of the "T 10" actually came from--guys' appetites increase and either they don't exercise to offset it or they choose foods that are super high in calories but don't really fill you up (aka junk food) and eat way more than they think they are. I think that as long as you monitor what you eat and do some light exercise, you should be okay. But don't assume you know how many calories you are eating! French fries or a slice of pizza can have a shocking number of calories in them. If you want to keep from gaining on T, you need to monitor what kind of foods you are downing with your increased appetite.
Just my personal opinion on the situation. 🙂