Type 2 diabetes -- especially in young people -- high blood pressure, cardiovascular disease, breast and colon cancer, arthritis and possibly Alzheimer's disease all may shorten U.S. lifespans, researchers at Northwestern University's Feinberg School of Medicine said.

"Obesity -- and its complications -- is the epidemic of our time," Dr. Lewis Landsberg, founder and director of the center and former dean of the Feinberg School, said in a statement. "There's been an astonishing increase in the obesity in the past two decades."

More than one third of U.S. adults -- more than 72 million people -- now are obese.

Landsberg traced the obesity epidemic to multiple causes: biological, evolutionary, psychological, sociological, economic and political. Obesity is programmed into our genes, he noted.

"The human race is heir to obesity because we evolved in a setting of intermittent famine, and those with more efficient metabolic systems were able to survive," Landsberg said. "In our genome is the predisposition to store excess calories. It serves us well when we're faced with a subsistence diet, but in the presence of an abundant food supply and dietary excess, it leads to obesity and diabetes."