Read the Column » For their Nov. 18, 2007, “Freakonomics” column, Dubner and Levitt revisit a favorite topic: unconventional weight loss. In September 2005, they wrote about Seth Roberts, who shed 40 pounds with a diet he crafted through years of meticulous self-experimentation. This week’s column digs into the risks and benefits of using surgery to combat obesity. This blog . . .