Probs due to youre metabolism, exercise, or what you eat. I have rubbish metablism, the only time I exercise is when I walk to the shop to buy fags, and I mainly eat processed, fatty crap. Starting to change some of that though, Im starting to eat more fruit and veg, and also going down town each day, if only to walk around. Might start going gym again soon so I can get a bit fitter, then move onto some form of self-defence class.