From the four food groups to the Food Pyramid, the U.S. government has long offered guidance to Americans hoping to eat a healthier diet. But there's growing scientific consensus that when it comes to eating healthy, all of us respond to foods differently. And to prove it, the National Institutes of Health has embarked on the most ambitious nutrition study ever, hoping to finally provide Americans a personalized answer to the question: "What should I eat?" Correspondent Lee Cowan reports.