I just remembered an important lesson that the guy sitting next to me on the plane from JFK to Dublin airport taught me:
Nothing is more important in life than your own health. Your health is more important than your family, friends... everything.
His rational was that if you do not take care of yourself, you will eventually be a burden on your family, thereby hurting them. That would be terrible. Therefore, worry about your own health, so that you may help/serve the ones you love. If that isn't motivating to eat healthy, I don't know what is!