A finnish study of identical twins found that physical inactivity and being obese can impair Expression of our Genes which helps the Cells produce and use energy. The study found that Lifestyle had a more profound effect on our health and longevity than heredity.
So in other words even if you have a family history of disease if you exercise and eat well you'll change your Genes to become healthy instead of diseased.
Lifestyle Can Alter Gene Activity, Lead To Insulin Resistance