During months like this, when the stock market becomes a pinball machine, it’s often difficult to explain the key causes behind the ups and downs of an individual security. That’s not the case when it comes to Weight Watchers’ stock price which, now more than ever, is directly tied to corporate investor and spokeswoman Oprah Winfrey. In a recent video, Oprah proclaimed: “I lost 26 pounds, and I have eaten bread every single day.” The company’s stock went up more than twenty percent. Maybe there are broader market forces at work. I’ve gained a few pounds this year and my entire portfolio is in the toilet.