The specific problem, as delineated in another forum: John and Bill are identical twins. Neither has smoked; neither drinks. John spent his time between the ages of 20 and 40 in the gym, working his hind end off and generally incurring the approval of his HMO. Bill spent ages 20 to 40 sitting in front of the TV, eating all the bad stuff you're supposed to eat in front of the TV. On their 40th birthday, John gives up his health-club membership and joins Bill in front of the TV. When they reach their 60th birthday (assuming they haven't killed each other arguing over the remote or politics or ???), should John be healthier than Bill, or will he have lost whatever advantage he had by having worked out for 20 years?