Many assume each generation of Americans will live longer but U.S. researchers say a new forecasting method indicates obesity may stem this progress. Eric N. Reither of the Utah State University in Logan; S. Jay Olshansky of the University of Illinois in Chicago; and Yang Yang of the University of North Carolina in Chapel Hill say most Americans enjoy better health than in the past, with significant declines in death rates from the top three causes of death -- heart disease, cancer and stroke. However, death rates provide "only a limited, 'two-dimensional' vision of the future by failing to take into account the potentially different risk factors accumulated by people who are still alive," the study authors say in a statement. Using heart disease mortality data from the National Center for Health Statistics, the researchers illustrate how traditional projection methods fail to account for the impact of the U.S. obesity epidemic on the longevity of younger Americans. The study, published in the journal Health Affairs, found traditional, two-dimensional methods predicted continued declines in mortality from coronary heart disease for men under age 50, but mortality rates slowed among men ages 45-49 and reversed among men ages 25-29 after 2000. "Because this three-dimensional perspective anticipates substantial increases in morbidity and related healthcare expenditures, it suggests that the appropriate public policy response is to redouble efforts to develop and implement effective obesity prevention programs and other targeted interventions," the study authors say.