Actually, the "Food Pyramid" was based on what nutritionists knew at the time. With all the advancements in medical technology and our knowledge of how the human body works, it's only understandable for them to revise their recommendations of what to eat, how much of it to eat, and so on. Science, as the late Carl Sagan once pointed out, is thus self-correcting - we're constantly updating the textbooks as our knowledge increases.