An curved arrow pointing right. Tim Ferriss, author of "The 4-Hour Workweek" and "Tribe of Mentors," is a firm believer in ketogenic diets and fasting. Here's why he believes so firmly in it.

Not only has his weekly podcast, The Tim Ferriss Show, now reached 80 million downloads, but the self-help guru drives sales of books, teas, sardines, toothpaste and any other product or tool he ...