Secondly, your own analogy is poor. It appears that being overweight directly relates to diabetes, and some qualitative theories on that have been developed (which are mentioned in the wiki article). So, weight increases diabetes. Eating more and excercizing less increases weight. So, you see what we got here? If A = B, and B = C, then A = C. Eating more an exercising less increases diabetes!
If you want to analogize to that, you could have said that having tarred lungs increases the odds of lung cancer. That would have been closer to what I was saying. Smoking tars your lungs, tarred lungs increases your odds of lung cancer. So... Smoking = increased lung cancer.