Its just not about being fat. Its not like everyone who has a heart attack or has disgusting goop clogging their arteries is obese or even overweight. A lot of them are skinny and have no idea that their triglyceride level and LDL is through the roof. Exercise does not totally compensate for all the bad things you eat, and the healthier your diet is when you're young, the less likely it will be that your doctor will tell you to get a triple bypass when you're 50.