Differences in the prevalence of obesity continue to explain about 20–35 percent of the shortfall in U.S. life expectancy relative to countries with superior levels, even when one uses much lower sets of obesity risks. http://www.ncbi.nlm.nih.gov/books/NBK62367/

(Published 2005) Over the next few decades, life expectancy for the average American could decline by as much as 5 years unless aggressive efforts are made to slow rising rates of obesity, according to a team of scientists supported in part by the National Institute on Aging (NIA), a component of the National Institutes of Health (NIH) of the Department of Health and Human Services (DHHS).  http://www.nih.gov/news/pr/mar2005/nia-16.htm