I'm sorry, I didn't want to sound like I was telling people what to do, I was just sharing what I have been taught in the dietology lessons I had at the university, as I found them interesting when I learned them. English is not my mothertongue so perhaps what I wrote had been misunderstood. You are right, we will never be sure whether we'll be sick because it was just going to happen anyway or because we smoked/ate something wrong/had any other bad habit. But, for example, if I have a lung cancer when I'll be older I know it was note caused by smoking because I don't smoke. If I smoked and I would then have a lung cancer, I would be never sure if it was caused by the smoking or if I would have had it anyway. It's like when you drive, you pay attention and try to not do any crash, but maybe you'll get involved in one anyway, right? In that case you are unlucky, but you know that it was not your behaviour that caused that.