Breakfast is the most important meal of the day." You've heard it your whole life. From doctors, nutritionists, health magazines. It's presented as established science. But this "fact" didn't originate in research labs or medical journals. It came from Kellogg's marketing department in the early 1900s. That's right—one of the most firmly-held beliefs in nutrition came from companies selling cereal, not from science studying human metabolism. And we've been following it ever since.